Silurus asotus (Amur catfish)
Datasheet Types: Natural enemy, Invasive species, Host animal, Cultured aquatic species
Abstract
This datasheet on Silurus asotus covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Management, Genetics and Breeding, Economics, Further Information.
Identity
- Preferred Scientific Name
- Silurus asotus Linnaeus, 1758
- Preferred Common Name
- Amur catfish
- Other Scientific Names
- Parasilurus asotus (Linnaeus, 1758)
- Parasilurus asotus asotus (Linnaeus, 1758)
- Parasilurus japonicus (Temminck & Schlegel, 1847)
- Silurus bedfordi Regan, 1908
- Silurus cinereus Dabry de Thiersant, 1872
- Silurus dahuricus Pallas, 1787
- Silurus dauuricus Pallas, 1787
- Silurus japonicus Temminck & Schlegel, 1846
- Silurus punctatus Cantor, 1842
- International Common Names
- EnglishChinese catfishFar Eastern catfishJapanese catfishKorean catfish
- RussianAmurskii som
- Chinesenien yú
- Local Common Names
- Chinakun yúlián zinián de yì míngnián yú
- DenmarkAmurmalle
- EstoniaAmuuri saga
- FinlandAasianmonniJapaninmonni
- GermanyAmurwels
- Japannamazu
- Korea, Republic ofmegi
- Polandsum amurski
Pictures
Adult
Silurus asotus (Amur catfish); Adult, caught at Lake Biwa, Japan. October 2007.
©Ryosuke Hosoi/via Flickr - CC BY 2.0
Female
Silurus asotus (Amur catfish); Adult female showing non-split tail.
©Dr. Ching Fui Fui
Male
Silurus asotus (Amur catfish); Adult male showing split tail.
©Dr. Ching Fui Fui
Overview
Taxonomy:
Kingdom (Animalia), Phylum (Chordata), Class (Actinopterygii), Order (Siluriformes), Family (Siluridae), Genus (Silurus), Species ( Silurus asotus )
Silurus asotus has several common names including Japanese catfish, Amur catfish ( Sariat et al., 2020 ) and Chinese catfish ( Fu et al., 2006 ), Far Eastern catfish ( Gil et al., 2017 ), Korean catfish ( Yu et al., 2009 ).
It is native to East Asia including Japan, China, Korea, Taiwan, the Russian Far East and the Northern region of Vietnam, with some introductions to neighbouring regions. In 2016, S. asotus was introduced to Malaysia where it is non-native, as a candidate aquaculture species. However, S. asotus in Malaysia is only for research purposes with no intention to produce it on a large aquaculture scale.
Silurus asotus has been shown to be hardy, allowing it to withstand stress during artificial spawning, handling, transportation and breeding. It has all of the necessary features for aquaculture, including a high fecundity, the capacity to spawn in captivity, a high tolerance for fluctuating water quality, a high resilience to infectious diseases, a low feed conversion ratio, rapid growth and a high survival rate. Similar to other catfishes, these traits make S. asotus one of the most attractive options for aquaculture.
FAO (2021) indicates that over 350,000 tonnes are produced per year in aquaculture in China. Scientific data indicates its great growth performance ( Sariat et al., 2020 ), high fecundity ( Dulmaa, 1999 ) and ease of cultivation, which are equivalent to other freshwater fish species; this strongly suggests that S. asotus be cultivated where it is native.
Silurus asotus is also recommended for cultivation in areas where it has been introduced but, because of its potential invasiveness, only under strict biosecurity conditions to avoid escape into the ecosystem.
Summary of Invasiveness
Silurus asotus is a large (maximum 130 cm) fish species of the order Siluriormes (catfish) mainly of value as a food fish but also as a sport fish (although rarely in Asia). It is native to East Asia including Japan, China, Korea, Taiwan, the Russian Far East and the Northern region of Vietnam. It has been introduced in waters in regions bordering its native range. As a freshwater species, it is confined to the river and lake catchments in which it presently resides, although its use of flooded agricultural land for spawning purposes has been argued as potentially increasing the likelihood of within-catchment spread. The potential for accidental introduction is relatively low; however, further intentional introductions for food and sport angling are possible – it has many characteristics making it very suitable for aquaculture and would almost certainly have a positive economic impact in this respect.
Little is known about the environmental impact of the species, but it is suspected of being invasive in non-origin nations, based on evidence of cannibalism in the larval and juvenile stages. Furthermore, its high fecundity and early maturity may result in rapid population increase in introduced areas, perhaps outpacing native species.
It has been introduced to Malaysia primarily for scientific purposes. Because of its potential invasiveness, it is recommended that any production outside the native range should be done in controlled systems with excellent biosecurity. No escapes have been observed to date in Malaysia.
Silurus asotus is listed as Least Concern (LC) in the IUCN Red List of Threatened species ( http://www.iucnredlist.org/ ).
Taxonomic Tree
Description
Dorsal soft rays: 4-6; Anal soft rays: 59-88 ( Kobayakawa, 1990 ). The stomach is white and there are irregular white dots on the flanks. Immature and adult fish have one pair of maxillary barbels which are longer than the head and one pair of mandibular barbels that are approximately 20 to 30% of the length of the maxillary barbel ( Liu, 1990 ). In juvenile fish (6-7 cm standard length), this species has one more pair of mandibular barbels ( Atoda, 1935 ). The maximum size of this species is 130 cm in total length (TL), but it is usually 30-60 cm TL ( Kobayakawa, 1989a ; Choi et al., 1990 ); maximum weight is 30 kg.
Pathogens Carried
Distribution
Silurus asotus is naturally found in lowland rivers, ponds and lakes in Japan, the Korean Peninsula, Taiwan, China and the Amur Basin of Russia ( Kobayakawa, 1989b ; Choi et al., 1990 ). In Japan, it is widely distributed in Honshu, Shikoku and Kyushu ( Kobayakawa, 1989a ). In the Korean Peninsula, it is distributed in North and South Korea apart from the east coast ( Uchida, 1939 ; Choi et al., 1990 ). On Taiwan Island, it is mainly distributed in the southern to northern area from the Central Mountains to the west ( Shen, 1995 ). In China, it is widely distributed in the main river systems ( Wu, 1982 ). In Russia, it inhabits Lake Khanka, the Ussuri and Razdolnaya rivers in Primorye and the Amur Basin ( Boutorina and Ermolenko, 2001 ; IUCN, 2023 ). IUCN (2023) reports that it is also found in central Vietnam and in parts of Mongolia, and has been introduced to the Lake Baikal basin in Russia.
Where can and should this species be cultivated?
Silurus asotus can be cultivated in its countries of origin. It can also be farmed in non-origin countries under very strict biosecurity measures in hatcheries, but not for grow-out in ponds or cages.
Where is it in fact cultivated?
Silurus asotus is currently cultivated in Korea ( Katya et al., 2014 ), China ( Wen et al., 2003 ), Japan ( Kumakura et al., 2003 ) and Malaysia ( Sariat et al., 2020 ). It is important to note that the production of S. asotus in Malaysia is for research purposes only. The great majority of cultivated production takes place in China ( FAO, 2021 ).
Distribution Map
Distribution Table
History of Introduction and Spread
Silurus asotus was initially introduced in 1932 in Lake Shaksha within the Russian part of the Selenga Basin and thereafter, dispersed into Mongolia, established in the Orkhon and Tuu Gol river basins and became common in Ugy Nur Lake ( Manchin and Dgebuadze, 2010 ). In 2016 it was introduced to Malaysia where it is non-native, as a candidate aquaculture species. However, this is only for research purposes under strict biosecurity with no intention to produce it on a large aquaculture scale.
Introductions
| Introduced to | Introduced from | Year | Reasons | Introduced by | Established in wild through | References | Notes | |
|---|---|---|---|---|---|---|---|---|
| Natural reproduction | Continuous restocking | |||||||
| Mongolia | Russian Federation | Yes | No | |||||
| Malaysia | Japan | 2016 | International organisation | No | No | |||
Risk of Introduction
As a valuable food and sport fish there is potential for further intentional introduction of S. asotus, although the level of risk has not been quantified.
Means of Movement and Dispersal
Natural Dispersal (Non-Biotic)
Natural dispersal may occur through laterally connected rivers and through flooded riparian agricultural land.
Pathway Causes
| Pathway cause | Notes | Long distance | Local | References |
|---|---|---|---|---|
| Fisheries (pathway cause) | Yes | Yes | ||
| Interbasin transfers (pathway cause) | Yes | Yes | ||
| Interconnected waterways (pathway cause) | Yes | Yes |
Pathway Vectors
| Pathway vector | Notes | Long distance | Local | References |
|---|---|---|---|---|
| Aquaculture stock (pathway vector) | Yes | Yes |
Similarities to Other Species/Conditions
Silurus asotus is similar in appearance to other members of the Siluridae family and is identified by the anterior edge of pectoral spine being prominently serrated; and the tooth band on vomer continuous ( Dai, 1999 ).
Anatomy
Larval sensory organs ( Mat Nawang et al., 2022 ):
In newly hatched larvae, no taste buds and free neuromasts were visible. The only sensory organ discovered was two otoliths in the inner ears, and small nasal pits were observed. At 6 h after hatching (hAH), the first free neuromasts appeared and the outlines of the nasal pits with cilia were clearly visible. By 12 hAH, free neuromasts increased and small taste buds appeared on the barbels and around the mouth. By 60 hAH, the epithelial layers increased so that the pigment appeared darker. At 5 hAH, taste buds and free neuromasts increased and three pairs of otoliths were identified in the inner ears. The olfactory pits of the larvae of the S. asotus were divided into an anterior and a posterior part.
Larval morphological development ( Mat Nawang et al., 2020 ; 2022):
In newly hatched larvae of S. asotus, the eyes were unpigmented, with the outer line forming. At 6 hAH (hours after hatching), slight black pigmentation was noted in the eyes and approaching 12 hAH, larvae had pigmented eyes and the mouth and anus were opened. At 30 hAH, the eyes were fully pigmented, the mouth was open, and the mandible was mobile while at 60 hAH, the tail tip began to bend 45° and the yolk sac became smaller. The eyes of the larvae were fully pigmented at 3 dAH (days after hatching). By 9 dAH, the caudal fin began to develop and fin rays were visible on both the anal and caudal fins; at 12 dAH S. asotus reaches the juvenile stage as the external morphology becomes more similar to that of an adult fish. At 20 dAH, a pair of mandibular barbels had degenerated.
Shape and colour of reproductive organs:
Sexually mature males of S. asotus can be distinguished by the presence of split caudal fins. Morphologically, the testes are long, highly vascularized, opaque and milky white in colour. Sexually mature females have greenish eggs (approximately 3-5 mm in diameter), and multiple developing eggs can be easily seen throughout their ovary under endoscopic observation.
Habitat
Mostly found in rivers, lakes, and reservoirs. S. asotus takes refuge in swamps and underwater caves during the day and feeds during the night. It prefers slow running water and a muddy bottom ( Huckstorf, 2012 ). It tends to stay in deep waters and muddy habitats during winter (Liu, 1990).
Habitat List
| Category | Sub category | Habitat | Presence | Status |
|---|---|---|---|---|
| Freshwater | Irrigation channels | Principal habitat | Natural | |
| Freshwater | Lakes | Principal habitat | Natural | |
| Freshwater | Reservoirs | Present, no further details | Natural | |
| Freshwater | Rivers / streams | Principal habitat | Natural |
Biology and Ecology
Genetics
The chromosome number of S. asotus is n=29, 2n=58 ( Klinkhardt et al., 1995 ). The total mitochondrial genome of this species is reported in Nakatani et al. (2011) .
Reproductive Biology
Spawning activity of S. asotus, takes place in temporary water (rice fields) in conjunction with the rainy season (late April to late August, depending on location). Thus, spawning tends to connected with hydrographic parameters dependent on rainfall, where increased daily precipitation, turbidity, water depth, and water temperature initiate spawning ( Maehata, 2007 ); these behaviours are presumed to be adaptations to the Asian monsoon climate that has a pronounced rainy season. The apparent sex ratio of the species is extremely biased toward females. Intraspecific variation in their reproductive ecology, particularly mating behaviour, has been is observed within local populations ( Maehata, 2007 ), for example the Biwa population shows a fixed sequence of actions, i.e. chasing, clinging, enfolding with squeezing by the male, and circling of the paired fish, and females are always enfolded by a single male ( Maehata, 2002 ), whereas the Ooi-, and Fuefuki-populations do not show such a behavioral sequence; the process of enfolding a female’s body by a male is not so stereotyped, circling by the paired fish has not been recognized, and females are often enfolded by two males ( Maehata, 2007 ). S. asotus scatter their eggs during spawning, a mechanism believed to be aimed at reducing juvenile mortality ( Katano et al., 1988 ).
In Mongolia, both males and females attain sexual maturity at the age of 4 to 5 years, at lengths of 350 to 370 mm. The spawning season starts in late May and ends at the end of July, peaking in mid-June. At the air temperature of 19°C, the larvae hatched on the 7th day after fertilization ( Huckstorf, 2012 ). In the delta of the Halhin Gol the spawning period is shorter, from the end of May until the end of June, when spawning occurs in the evening and at night at water temperatures of 16-18 o C. They lay their eggs in stagnant water on submerged aquatic macrophytes at depths of between 0.1 and 0.7 m. In the Halhin Gol delta, spawning females tend to be 400 to 600 mm and males 300 to 400 mm long, where female fecundity ranges from 29,470 to 70,850 eggs. By contrast, in Lake Buyr, it is 22,190 to 92,750 eggs. In Lake Ugiy in the Selenga catchment, S. asotus of 510 to 740 mm and 1200 to 3000 g weight have fecundity of 33,900 to 128,200 eggs ( Dulmaa, 1999 ).
Longevity
Amur catfish are reported to live for a maximum of 12 years ( Dulmaa, 1999 ).
Activity Patterns
This species enters the littoral zone of rivers and lakes at the end of April to beginning of May prior to spawning and after the ice cover has melted; in this period they are vulnerable to capture by fishermen. In summer, they stay close to shores and river banks, and some enter channels connecting rivers with floodplains. They are commonly found among the flooded terrestrial vegetation. In autumn they leave inshore waters for deeper channels and pools in the main river where they overwinter. In captivity, in seed production of this species, biting and cannibalistic behaviour were recognized about 40 d after hatching, inducing high mortality( Yada and Furukawa, 1999 ).
Nutrition
Silurus asotus is a piscivorous species, feeding on all kinds of fish; it also consumes frogs and insects (Wu, 1982; Kobayakawa, 1989a ; Dulmaa, 1999 ).
Climate
| Climate type | Description | Preferred or tolerated | Remarks |
|---|---|---|---|
| Cs - Warm temperate climate with dry summer | Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers | Preferred | |
| Cw - Warm temperate climate with dry winter | Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters) | Preferred | |
| Dw - Continental climate with dry winter | Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters) | Preferred | |
| Af - Tropical rainforest climate | > 60mm precipitation per month | Preferred |
Latitude/Altitude Ranges
| Latitude North (°N) | Latitude South (°S) | Altitude lower (m) | Altitude upper (m) |
|---|---|---|---|
| 23-53 |
Air Temperature
| Parameter | Lower limit (°C) | Upper limit (°C) |
|---|---|---|
| Mean annual temperature | 5 | 25 |
| Mean maximum temperature of hottest month | 30 | 34 |
Water Tolerances
| Parameter | Minimum value | Maximum value | Typical value | Status | Life stage | Notes |
|---|---|---|---|---|---|---|
| Water temperature (°C temperature) | 26 | 33 | 28 | Optimum | Aquatic|Broodstock | |
| Water temperature (°C temperature) | 28 | 30 | 28 | Optimum | Aquatic|Egg | |
| Water temperature (°C temperature) | 28 | 30 | 28 | Optimum | Aquatic|Larval | |
| Water temperature (°C temperature) | 27 | 33 | 28 | Optimum | Aquatic|Fry | |
| Dissolved oxygen (mg/l) | 4.5 | 8 | 7 | Optimum | Aquatic|Broodstock | |
| Dissolved oxygen (mg/l) | 6 | 7 | 6.5 | Optimum | Aquatic|Egg | |
| Dissolved oxygen (mg/l) | 6 | 7 | 6.5 | Optimum | Aquatic|Larval | |
| Dissolved oxygen (mg/l) | 6 | 8 | 7 | Optimum | Aquatic|Fry | |
| Salinity (part per thousand) | 0 | 0 | 0 | Optimum | Aquatic|All Stages | |
| Water pH (pH) | 7 | 7 | 7 | Optimum | Aquatic|Broodstock | |
| Water pH (pH) | 5 | 6 | 6 | Harmful | Aquatic|Broodstock | |
| Water pH (pH) | 7 | 7 | 7 | Optimum | Aquatic|Egg | |
| Water pH (pH) | 5 | 6 | 6 | Harmful | Aquatic|Egg | |
| Water pH (pH) | 7 | 7 | 7 | Optimum | Aquatic|Larval | |
| Water pH (pH) | 5 | 6 | 6 | Harmful | Aquatic|Larval | |
| Water pH (pH) | 7 | 7 | 7 | Optimum | Aquatic|Fry | |
| Water pH (pH) | 5 | 6 | 6 | Harmful | Aquatic|Fry |
Diseases, Disorders and Natural Enemies
Health
This species is highly resistant to stress and external injury as it can survive wounds due to its unique epidermal mucus lectin. It has a maximum life expectancy of 12 years ( Im et al., 2000 ). Although S. asotus is known to be hardy and able to tolerate a wide range of diseases, several cases of mass mortality triggered by disease have been reported including:
•
Yu et al. (2009) reported mass mortality of farmed S. asotus infected with Edwardsiella tarda, one of the serious fish pathogens affecting other common aquaculture fish.
•
Kim et al. (2019) reported the first tetracycline-resistant Aeromonas veronii infection of S. asotus.
•
Moravec and Justine (2008) reported parasite Philometra parasiluri infection of S. asotus .
•
Yang et al. (2015) - malformation of S. asotus affecting skeletal development.
Predation
Birds of prey are the only predators in a hatchery with a closed system. Snakes, birds, otters, fish and monitor lizards are some of the predators of S. asotus in the wild.
List of Diseases and Disorders
Natural enemy of
Natural enemies
| Natural enemy | Type | Life stages | Specificity | References | Biological control in | Biological control on |
|---|---|---|---|---|---|---|
| birds | Predator | Aquatic|All Stages | not specific | |||
| monitor lizard (Varanus salvator) | Predator | Aquatic|Adult | not specific |
Impact Summary
| Category | Impact |
|---|---|
| Cultural/amenity | Positive |
| Economic/livelihood | Positive |
| Environment (generally) | Positive and negative |
| Fisheries / aquaculture | Positive and negative |
Impact: Environmental
Little is known about the environmental impact of this species. However, as S. asotus is a large (up to 130 cm long) piscivorous species that feeds on all kinds of fish ( Dulmaa, 1999 ), it may form a threat to native fish species in areas where it is introduced (A. Gittenberger, Gimaris, The Netherlands, personal communication, 2011).
Interspecific hybridization is common in a variety of taxonomically distinct fish species, but there are no reports of hybridization between S. asotus and other freshwater fishes. However, the possibility exists because S. asotus has a high fecundity that allows it to spawn year-round when water temperatures are optimal in the natural ecosystem.
Mat Nawang et al. (2022) reported that S. asotus exhibits active feeding behaviour from the larvae to juvenile stages, so food competition may occur and might contribute to negative impact on biodiversity. S. asotus also stays predominantly at the bottom of the water from the larval to juvenile stages, so competition for space may occur in the natural habitat, especially with benthic fishes.
Silurus asotus is also easily attacked by parasites ( Moravec and Justine, 2008 ) and might transmit diseases to other fish species. However, all kinds of fish species are vulnerable to parasites in the natural ecosystem since they are an essential part of the ecosystem and provide some level of population control to keep the ecosystem in balance.
Environmental Impact of Culture
There is no indication of environmental impact of culture of S. asotus . Its low feed conversion ratio helps to minimize waste and water pollution in the environment.
Risk and Impact Factors
Invasiveness
Abundant in its native range
Capable of securing and ingesting a wide range of food
Highly mobile locally
Benefits from human association (i.e. it is a human commensal)
Long lived
Has high reproductive potential
Gregarious
Uses
Economic Value
In Mongolia and Japan, S. asotus is an important commercial fish species. In the 1920s, during the winter fishing period in Mongolia, the following quantities were captured: in 1923/1924 - 480 t, in 1924/1925 - 430 t, in 1925/1926 - 370 t. In Lake Buyr, during the 1959-1969 period, the average annual catch was 37.7 t. However, by the end of the 1990s, catches of S. asotus from Lake Buyr had declined to approximately 10 t/year. In Lake Ugiy, S. asotus represents less than 1% of the total catch ( Dulmaa, 1999 ). Silurus asotus is currently cultivated in Korea (Katya et al., 2014), China (Wen et al., 2003), Japan (Kumakura et al., 2003) and Malaysia (Sariat et al., 2020). It is important to note that the production of S. asotus in Malaysia is for research purposes only. The great majority of cultivated production takes place in China (FAO, 2021).
Social Benefit
S. asotus is also a sport fish. The record weight for a line-caught specimen is 20 kg, of a length of 132 cm ( http://www.fishing-worldrecords.com ).
Environmental Services
S. asotus is the most common predator of shallow waters. It feeds on all types of fish, and it is important for its regulatory effects on fish such as crucian carp ( Carassius carassius ), ide ( Leuciscus idus ) and wild carp ( Dulmaa, 1999 ).
They may also be used in the control of non-native species, as research suggests that the introduction of these catfish into ponds and lakes for the purpose of eradicating bluegill ( Lepomis macrochirus ) is appropriate for areas with few native fish species. In the case that only bluegill and catfish were introduced in ponds in Japan, catfish consumed 4 to 15 g of bluegill per day ( Katano et al., 2005 ).
Uses List
General > Sport fish
Environmental > Biological control
Human food and beverage > Fresh meat
Human food and beverage > Live product for human consumption
Human food and beverage > Meat/fat/offal/blood/bone (whole, cut, frozen, canned, cured, processed or smoked)
Products
Silurus asotus is used as a source of meat for human consumption.
Detection and Inspection
The stomach of S. asotus is white and it has irregular white dots on its flanks. It has one pair of maxillary barbels which are longer than the head and one pair of mandibular barbels that are approximately 20 to 30% of the length of the maxillary barbel ( Liu, 1990 ). For further information on field identification see Dai (1999) .
Behaviour
General behaviour (Larvae to juvenile stage) ( Mat Nawang et al., 2022 )
Newly hatched larvae (0 to 6 h after hatching): Stayed at the bottom, negative phototaxis response, negative immediate rheotaxis response.
12 h after hatching: Swam in vertical and horizontal, positive phototaxis response, positive immediate rheotaxis response.
30 h after hatching: Larvae start first feeding, swim at bottom and occasionally in vertical direction, swam to the surface when feeding, positive phototaxis response, positive immediate rheotaxis response.
5 days after hatching: Swim up and down, obvious active swimming behaviour when feeding, predominantly stay at the bottom and start to be active both day and night.
20 days after hatching: Shifted to bottom feeder behaviour, prefer to stay where substrate is available.
Under laboratory observation, cannibalistic behaviour has been observed in S. asotus from larvae to juvenile stages, where they tend to attack and cannibalize despite adequate diet and low stocking density ( Mat Nawang et al., 2022 ; Yada and Furukawa, 1999 ). These findings point to the likelihood that S. asotus could predate other fish if released into the wild. S. asotus greater than 4 inches in length, on the other hand, have been discovered to be non-cannibal.
Stress-related behaviour
Silurus asotus refuses to eat when feed is given under stress conditions. Similar behaviour has been observed from larvae to adult stages.
Reproduction
Silurus asotus can be cultivated in its countries of origin either by natural spawning (limited to 1-2 times per year) or by hormone injection in a closed system in a hatchery (heating must be available to ensure a water temperature of 28-29 degrees) ( Sariat et al., 2020 ). Low water stimulation can also be used to induce spawning. (It can also be farmed in non-origin countries under very strict biosecurity measures in hatcheries as food fish, but not for grow-out in ponds and cages).
Low water stimulation involves reducing the water level so that it is just sufficient to submerge the body of the fish, typically up to its dorsal fin, for about 24 h. This works because in natural habitats, low water levels can be associated with a variety of factors favouring spawning, such as higher temperatures, availability of spawning sites, migration to such sites, changes in photoperiod and reduced oxygen levels stimulating spawning as a survival strategy.
Size at maturation: Spermatozoa were detected in all male S. asotus samples which indicated a mature gonad. Thus, male S. asotus can mature as early as 3 months of age under controlled temperatures and with an average body weight of 146 g ( Sariat et al., 2020 ). In female gonads, the histology results showed a large variation in the oocyte stage. Frequent feeding compared to the wild hastened the onset of maturation. Maximum size of matured females is 1.8 kg and that of males is 1.0 kg.
According to Kumakura et al. (2003), in temperate zones, most teleost fish including S. asotus are seasonal spawners and there is variation in the time of year when spawning occurs. However, when S. asotus is cultured under a tropical climate (in hatchery) the high and constant temperature is responsible for all year-round spawning in captivity.
One cycle per month is possible when spawning is stimulated by hormone injection or low water; this information is not available for natural spawning.
Broodstock culture conditions in Universiti Malaysia Sabah (UMS) Fish Hatchery
1. Production system
15 females and 15 males of S. asotus with the average sizes 350 g should be reared in a round tank with 10 tonnes of water capacity. Tank should be well aerated to 300 ml/min and a greenwater system should be introduced to further enhance water quality and minimize direct light penetration into the water. Approximately 10% of water renewal should be done on a daily basis. Fish health and growth should be checked and recorded on a monthly basis to maximize fish welfare.
2. Water sources
Filtered and chlorine-free water should be introduced.
3. Water parameter
▪ Temperature: 27.5±0.9°C
▪ Dissolved oxygen: 7.4±0.20 mg/L
▪ pH: 7.0±0.3
4. Feeding Management
Feed types:
▪ Marine formulated pellet, size 4-6mm (crude protein: 45%, crude lipid: 8%)
▪ Fresh prey fish
Fresh prey fish are given alternately with marine formulated pellets to further support maturation of S. asotus . The fish should be fed with an amount equivalent to at least 6% of their body weight, once per day.
5. Spawning method ( Mat Nawang et al., 2020 )
Artificial stripping method
- Broodstock selection
Good candidates for broodstock should be selected with a female:male ratio of 2:1. The females and males should be selected based on their round belly with no injury and deformities and shape of their genital papilla.
- Hormone injection and water stimulation
Fish should be stocked with the water level up to their dorsal fin height for 10 h and then injected with hormone at the dosage of 5 mg/kg of fish body weight.
- Egg and sperm stripping
The eggs and sperm should be stripped after 6 h (depends on egg maturation stage). The eggs should be stripped into a plastic bowl with a thin layer of oil (Vaseline). Then sperm will be collected using a sperm bottle collector before mixing it into the bowl which contains the eggs. The eggs and sperm will be mixed using soft brushes for fertilization before distributing incubation tanks.
Egg nursery conditions
1. Egg collection system
The fertilized eggs should be incubated in a 60 L rectangular tank with a recirculating aquaculture system (RAS). The water should be well-aired to 100 ml/min and maintain a temperature of 28.0 ± 1.3°C until the eggs hatch. After hatching, larvae should be syphoned by using a hose to collect all larvae and transfer to the larval rearing system.
2. Water sources (similar method as previous)
Filtered and chlorine-free water should be introduced.
3. Water quality
- Temperature : 28.0 ± 1.3°C
- Dissolved oxygen : 6.7 ± 0.3 mg/L
- pH : 7.0 ± 0.4
4. Egg development observation method
The egg development can be observed under the microscope to observe the eggs' stage and the embryonic data collection should be calculated on their fertilization rate, development rate and hatching rate.
Larval nursery conditions
1. Larval rearing system
The larvae should be reared in a 60 L rectangular tank with a recirculating aquaculture system (RAS). The water should be well-aerated to 150 ml/min. Bottom cleaning and 20% water exchange every day should be done to make sure the water condition maintains in normal range. Bottom cleaner equipment should be suitable to remove waste particles and also to prevent the larvae being flushed out from the rearing tank.
2. Water source
Filtered and chlorine-free water should be introduced.
3. Water quality
· Temperature : 27.0 ± 1.3 °C
· Dissolved oxygen : 6.7 ± 0.3 mg/L
· pH : 7.0 ± 0.4
4. Feeding management
Larvae should be fed at least five times per day until satiation using suitable feed such as rotifer, Moina and formulated pellet powder. The feeding transition from live feed to artificial feed should depend on the open lower jawed size of the larvae.
Fry nursery conditions
1. Juvenile rearing system
There are two types of juvenile rearing system: using closed system with well-aerated green water system, and recirculating aquaculture system (RAS). The aeration rate should be at 200 ml/min. The bottom cleaning should be done twice a day. Weekly measurement and sorting should be done for juvenile growth records and to prevent cannibalism.
2. Water source
Filtered and chlorine-free water should be introduced.
3. Water quality
Temperature : 27.0 ± 1.3°C
Dissolved oxygen : 6.7 ± 0.3 mg/L
pH : 7.0 ± 0.4
4. Feeding management
Juveniles should be fed at least two times per day until satiation using formulated marine pellets. The formulated marine pellet sizes should change depending on the size of the juveniles.
Growout Management Table
| Ecosystem | Growout systems | Inland | Coastal | Adult stocking density (/m 3 ) | ||
|---|---|---|---|---|---|---|
| Extensive | Semi-intensive | Intensive | ||||
| Ecosystem-independent systems | ||||||
Growout Management
No specific information was available to the author on growout management in ponds or cages, or on culture systems used in China.
Growout under hatchery system in Universiti Malaysia Sabah Fish Hatchery (Fry to adult stage) is as follows:
Fry
•
Harvesting strategy: Water should be drained out 90% and nylon type of handnet (5 mm) should be used to harvest fry.
•
Transport and handling: No anaesthesia needed to immobilize fry prior to transport and handling. Fry will be left unfed for at least 1 day before handling them to be harvested and transported.
•
Temperature: Temperature: 28-30 degrees Celsius. Dissolved oxygen: 5-8 mg /L, pH: 6-8. Avoid transferring fry during rainy days.
Adult
•
Harvesting strategy: Water should be drained out 90% and nylon type of handnet (15 mm) should be used to harvest adults; canvas type of fish carrier should be used to transport them. During harvesting, damped cloth should be used to cover adults placed in a plastic basin.
•
Transport and handling: No anaesthesia needed to immobilize adults prior to transport and handling. Adults will be left unfed for at least 1 day before handling them to be harvested and transported.
•
Temperature: Temperature: 28-30 degrees Celsius. Dissolved oxygen: 5-8 mg /L, pH: 6-8. Avoid transferring adults during rainy days.
As mentioned in the Nutrition and Feeding section, food availability is enhanced by growing the fish in a greenwater system, fertilized to encourage the growth of a mixture of plankton and bacteria which (a) serve as the primary food source for zooplankton which the fish eat and (b) provide shade. A water exchange rate of 10-20% daily is needed for water renewal purposes.
Seed Supply and Species Availability
In Malaysia, wild S. asotus (40 g) was taken from Japan by Kindai University and shipped to Universiti Malaysia Sabah, Malaysia, via a research permit granted by the Department of Fisheries Sabah (Malaysia) in 2016. S. asotus were kept under quarantine for a week to examine their health condition. To date, all seed of S. asotus has been produced by artificial spawning via the hormone injection or low water stimulation methods and reared under a closed system.
Information on other countries was not available to the compiler of the datasheet.
Reproduction and Seed Production Systems
Reproduction Conditions
| Parameter | Value | Remarks | ||
Fertilization | Internal | Yes | ||
External | ||||
Reproductive guild | Non-guarders | Open water | ||
Benthic spawners | Yes | |||
Brood hiders | ||||
Guarders | ||||
Bearers | External | No Information | ||
Internal | No Information | |||
Migration | No Information | |||
Broodstock Conditions
| Parameter | Value or range | Remarks | |
Breeding | Induced | Yes | Hormone injection |
Natural | Yes | Low water stimulation | |
Mode | Assisted | Yes | Hormone injection |
Unassisted | Yes | Low water stimulation | |
Production system | |||
Culture system Stocking density (kg/m 3 ) | Extensive | Yes | Able to be cultured in wide range of culture system |
Semi-intensive | Yes | ||
Intensive | Yes | ||
Sex ratio male/female | 1:1 | ||
Actual number males | |||
Actual number females | |||
Egg production/kg | 75 g (approx. 37,500 eggs) per 1 kg female | ||
Mortality (%) | 20-50% | ||
Egg Nursery Conditions
| Parameter | Value or range | Remarks | ||
Production system | RAS system | |||
Culture system Stocking density (kg/m 3 ) | Extensive | |||
Semi-intensive | ||||
Intensive | Yes | RAS intensive | ||
Production | Egg mortality (%) | 20-50% | ||
Eyeing(day-degrees) | 12 h after hatching | |||
Time to hatch(day-degrees) | ||||
Time to hatch (hours) | 27 h after fertilization | |||
Production/cycle | ||||
Production/year | 12 cycles per year (hormone injection method) | |||
Illumination (Lux) | 1000 lux | |||
Larval Nursery Conditions
| Parameter | Value or range | Remarks | ||
Production system | Yes | RAS system | ||
Culture system Stocking density (kg/m 3 ) | Extensive | |||
Semi-intensive | ||||
Intensive | Yes | RAS system | ||
Growth rate | ||||
Production | Time to fry (days) | 20 days after hatching become fry | ||
Time to fry(day-degrees) | ||||
Mortality (%) | 6% | |||
First feed(day-degrees) | ||||
First feed (days) | 2 days after hatching | |||
Production/cycle | ||||
Production/year | ||||
Illumination (Lux) | 750 lux | |||
Fry Nursery Conditions
| Parameter | Value or range | Remarks | ||
Production system | RAS System and closed system | |||
Culture system Stocking density (kg/m 3 ) | Extensive | Yes | Able to be cultured in wide range of culture systems | |
Semi-intensive | Yes | |||
Intensive | Yes | |||
Growth rate | ||||
Production | Time to alevins (days) | 0-30 h after hatching | ||
Time to alevins(day-degrees) | ||||
Mortality (%) | 10% | |||
Production/cycle | ||||
Production/year | ||||
Illumination (Lux) | 1000 lux | |||
Artificial Food Sources
| Food source | Life stages | Contribution to total food intake (%) | Feeding methods | Feeding frequency | Feeding characteristics | Details |
|---|---|---|---|---|---|---|
| Marine Sinking pellet | Aquatic|Broodstock | Feeding tray | Once per day | Dry sinking pellet | 6% of body weight. Pellet size:17.0 -18.5 mm | |
| Marine Sinking pellet | Aquatic|Adult | Feeding tray | Once per day | Dry sinking pellet | 6% of body weight. Pellet size:13.0 -14.0 mm | |
| Marine Sinking pellet | Aquatic|Fry | Handfeed | Twice per day | Dry sinking pellet | Pellet size: 3.9 - 4.5 mm | |
| Otohime pellet | Aquatic|Larval | Handfeed | Every hour | Granule | Pellet size: 0.36 - 0.65 mm | |
| Rotifers | Aquatic|Larval | Every hour | Live feed (rotifer) should be given at 30 individuals/L based on the volume of water where S. asotus larvae are being cultured for first 72 h after hatching | |||
| Artemia (brine shrimp) | Aquatic|Larval | Live feed. Stocking density of Artemia should be increased from 1-5 individuals/L as larvae enter juvenile stages from 3 to 18 days after hatching. | ||||
| Artemia (brine shrimp) | Other|Juvenile | Twice per day | Live feed. Stocking density of Artemia should be increased from 1-5 individuals/L as larvae enter juvenile stages from 3 to 18 days after hatching. | |||
| Moina | Other|Juvenile | Twice per day | Live feed. 5 individuals/L, from 5 to 14 days after hatching | |||
| Prey fish (Big eye scad and squid) | Aquatic|Adult | Once per day | Weight of prey fish given should be based on body weight of fish -- 6% of body weight |
Nutrition and Feeding
Feeding regimes of S. asotus in Universiti Malaysia Sabah Fish Hatchery:
1. Broodstock
1. Type of food:
i. Trash fish
ii. Marine pellet (Protein:43%, Lipid:8%)
iii. Squid (enrichment before artificial production)
2. Amount of food: Until satiation
3. Frequency of feed given: Once per day
2. Larval
1. Type of food:
i. Live feed (Rotifer, Brachionus plicatilis )
ii. Formulated feed (Otohime)
2. Amount of food: Until satiation
3. Frequency of feed given: Every 1 h during daytime
3. Juvenile
1. Type of food: Marine pellet (Protein:43%, Lipid:8%)
2. Amount of food: Until satiation
3. Frequency of feed given: Twice per day (AM and PM)
4. Adult
1. Type of food:
i. Trash fish
ii. Marine pellet (Protein:43%, Lipid:8%)
2. Amount of food: Until satiation
3. Frequency of feed given: Once per day
Food availability is enhanced by growing the fish in a greenwater system, fertilized to encourage the growth of a mixture of plankton and bacteria which serve as the primary food source for zooplankton which the fish eat (and also provide shade).
Genetics
The chromosome number of S. asotus is n=29, 2n=58 ( Klinkhardt et al., 1995 ). The total mitochondrial genome of this species is reported in Nakatani et al. (2011) .
Breeding
| Trait | Comments | Score | References |
|---|---|---|---|
| Reproduction |
Performance
Scientific data indicate that the species has great growth performance ( Sariat et al., 2020 ), high fecundity ( Dulmaa, 1999 ), and ease of cultivation, which are equivalent to other freshwater fish species, especially catfish. This strongly suggests that S. asotus be cultivated where it is native. (It is also recommended for cultivation in areas where it has been introduced but, because of its potential invasiveness, only under strict biosecurity conditions to avoid escape into the ecosystem.
Larvae: 0-20 days after hatching (34.10±0.89 mm)
Juvenile/fry: 20-90 days after hatching (5.0±3.0 g)
Adult: 90 days onwards (5 to 250 g)
Maturation size: 180 days after hatching (250.0±50 g)
Size at harvest: 500 g for edible size
FCR: 1.8
Marketing
In Japan, the market of S. asotus is promising since a Japanese scientist has claimed this fish is able to replace the endangered Unagi Kabayaki (Japanese eel, Anguilla japonica ) ( Nikkei Asia, 2016 ).
Economic and Socioeconomic Aspects
Production, Economic and Socioeconomic Aspects
Aquaculture
Rapid growth and high fecundity have made S. asotus a popular aquaculture species, predominantly in China, where FAO (2021) indicates that over 350,000 tonnes are produced per year. S. asotus (presumably from capture fisheries) is a popular and valuable food fish in Indochina, Vietnam, Japan and Mongolia ( Kim et al., 2001 ), and its demand has increased due to its excellent organoleptic quality. To date, only Korea and Malaysia have reported aquaculture production of S. asotus outside China, with Gil et al. (2017) reporting over 8000 tonnes of this species through artificial production in Korea, while in Malaysia S. asotus has been produced only for research purposes by Sariat et al. (2020) and Mat Nawang et al. (2022). The results indicate that S. asotus can be captive-bred throughout the year due to its rapid maturation and high fecundity, surpassing the excellent performance of African catfish ( Clarias gariepinus ). Given the high consumption rate and fish intake by the growing Asian population, S. asotus is expected to provide significant economic benefits to the aquaculture industry and suppress the high wild take from the natural ecosystem.
Aquaculture is an important source of fish protein, and freshwater fish farming is more cost-effective and sustainable compared to marine aquaculture. Production of S. asotus is practically easy, similar to other hardy freshwater species that usually have high tolerance to disease and handling stress, so they can be mass produced in less than 6 months ( Sariat et al., 2020 ). To date, aquaculture production of S. asotus in Korea and Malaysia is conducted under controlled conditions, and no accidents or escapes into the natural ecosystem have been reported.
In Vietnam, S. asotus are harvested from the wild throughout the year, hence aquaculture production is necessary to suppress overfishing pressure while providing sufficient food for the increasing fish consumption rate in Vietnam ( Huckstorf, 2012 ; Gil et al., 2017 ).
In Korea, 8000 tonnes of S. asotus are produced annually through aquaculture, and this effort should continue and serve as an excellent example for other countries ( Yang et al., 2015 ).
In Malaysia under a research programme, a total of 900 kg of S. asotus are being produced annually, although this is only for research purposes with no intention to produce it on a large aquaculture scale.
In Japan and Mongolia, S. asotus is a commercially important species ( Dulmaa, 1999 ; Froese and Pauly, 2012 ) and it may provide an economic benefit as a sport fish because of its large size.
Economics
Freshwater fish aquaculture supports the livelihoods of a huge number of economically disadvantaged people in many parts of the world. Although S. asotus has not been widely farmed outside China, it has been demonstrated to grow quickly and can be mass-produced to meet the protein needs of an expanding human population. S. asotus, like other catfish species, can be mass produced at a lower cost due to its lower feed conversion ratio ( Holeh et al., 2020 ). As a result, feed intake can be reduced for the same amount of growth, lowering feed costs and environmental consequences while improving economic value.
Prospects
Future Prospects
Silurus asotus is a promising candidate aquaculture species both in its origin countries and elsewhere. There are several advantages of S. asotus as an aquaculture species ( Holeh et al., 2020 ; Mat Nawang et al., 2020 ; Sariat et al., 2020 ), including:
•
Fast growth (short larval and juvenile period, edible size 500 g in 7 months)
•
Survival rate (above 90% for all stages from larvae to adult)
•
Easy to cultivate (hardy species and able to tolerate wide range of water parameters, low handling stress)
•
High fecundity (mature at 250 g within 6 months)
•
Easy spawning method (hormone injection and low water stimulation method)
•
High disease resistance (unique epidermal mucus lectin for protection from disease)
Good meat quality (proven by Japanese researchers - Nikkei Asia, 2016 ).
Silurus asotus exhibits similar characteristics to the African catfish ( Clarias gariepinus ) ( Sariat et al., 2020 ), so its production could reach a similar level.
Gaps in Knowledge/Research Needs
There is relatively little information available on this species and the potential for depredation of native species is an unexplored risk.
Links to Websites
| Name | URL | Comment |
|---|---|---|
| GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway | https://doi.org/10.5061/dryad.m93f6 | Data source for updated system data added to species habitat list. |
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