New insights into hatchery production of freshwater catfish
Recreational Fishing Grants Program Research Report
Freshwater catfish (Tandanus tandanus) is a popular freshwater angling species in rivers of the Murray-Darling Basin (MDB). In recent decades the species has, however, undergone substantial declines in abundance and distribution. In Victoria, freshwater catfish is listed as threatened under the Flora and Fauna Guarantee Act 1988, occurring in small isolated populations only.
In 2011, Native Fish Australia (NFA), (Wimmera) Inc. received funds from the Department of Economic Development, Jobs, Transport and Resources
(former) Department of Primary Industries' Recreational Fishing Grants Program to help restore Victoria's recreational fishery by captive breeding and re-stocking freshwater catfish. The aim of this study was to observe spawning trials on freshwater catfish to produce juveniles for restocking into Victorian waters. Spawning trials focused on use of Ovaprim® to induce ovulation and spermiation in fish that where hand-stripped, and Ovaplant® (Syndel, Canada) to enhance maturation and ovulation in fish allowed to spawn naturally.
Nineteen females and 26 males were used in spawning trials conducted in late October 2013, when water temperatures approached 20oC. Tetrauronema, a new myxozoan parasite of freshwater catfish, was observed in a milt sample from one fish. The implications of the presence of this parasite in freshwater catfish is unknown.
Most females (70%) injected with Ovaprim were induced to spawn. Broodstock implanted with Ovaplant and transferred to a 0.15 ha pond containing patches of gravel subsequently spawned naturally within a month of being implanted.
Small amounts (0.1-1.0 mL) of milt, which was generally watery in consistency, was stripped from males. There was a slight improvement in both milt consistency and sperm activity 2 days after injection with hormones.
Relative fecundity of stripped females was low (920-3,370 eggs/kg). Although fertilisation rates (65-100%) were generally high, hatch rates (0-42%) were low and a high proportion (10-20%) of larvae were deformed. These results suggest that not all oocytes in the ovary were mature and consequently, responded to the hormone treatment, and/or fish were not fully conditioned for spawning. Spawning trials are likely to have occurred at the very beginning of the spawning season and so fish may not have been fully mature, which may affected fecundity, gamete quality, hatch rates and larval quality.
Fry were reared to fertilised earthen pond, and on 7thFebruary 2014, 1,900 fingerlings were harvested, 1,400 of these were released into Moodemere Lake (Rutherglen) and 500 into Crusoe Reservoir (Bendigo).
Observations made during these trials will be used to guide future R&D to improve captive breeding of freshwater catfish. Recommendations include:
- Increase broodstock numbers to increase productivity
- Reduce broodstock densities in ponds to optimise growth, conditioning and maturation
- Supplement the diet of broodstock with live prey (small yabbies)
- Remove the fish infected with Tetrauronema to reduce the risk of spreading the disease to other stock
- Check for the presence of this parasite in other broodstock during the next spawning season
- Undertake induced spawning later in the season, once water temperatures exceed 21oC and before reach 25oC (i.e. early to mid-November)
- Inject females and males to be hand-stripped each with a single doses of Ovaprim at 0.5 ml/kg
- Repeat natural spawning trials to obtain further information on production levels for comparison with to induced spawning and hand-stripping methods
- Rear fry into a pond by themselves using standard fry rearing methods employed for other native fish species.
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