PEFORMANCE OF SILVER PERCH (Bidyanus bidyanus)

IN A RECIRCULATING AQUACULTURE SYSTEM (RAS).

 

Phil Read

NSW Fisheries Extension Service

 

 

INTRODUCTION

 

 

A small RAS was constructed at the Grafton Aquaculture Centre for experimental and extension purposes. The 16,000 litre system consists of 12 x 1000L tanks, 2 x 500L swirl separators, a model 501 Hydrotech drum filter, a sump, a foam fractionator, UV, a heater/chiller unit, header tank and trickle biofilter, and a down-flow bubble contactor. Water flows via gravity from the tanks to the solids removal unit and sump; water is pumped to the header tank and biofilter returning via gravity to the production tanks. Bottled oxygen can be injected when required.

 

Two experiments evaluated the performance of silver perch in the RAS; (i) grow-out and (ii) over-wintered fingerlings. Water quality variables, alkalinity, dissolved oxygen, total ammonia (TAN), nitrite, nitrate, salinity, temperature and pH were monitored at least 3 days/week. Alkalinity and pH were regulated with the addition of sodium bicarbonate. Water was exchange at 3% per day.

 

RESULTS

 

Grow-out experiment. Fingerlings, (mean weight 43g) were stocked into 9 tanks at densities of 50, 100 and 200 fish/m3 and cultured at ambient temperatures for 224 days (7.5 months) from July to March. Each treatment had three replicate tanks and fish were sampled monthly. Fish were fed a formulated diet, containing 52% protein; initially, twice daily, up to 3% of estimated body weight, then to satiation. At termination, fish stocked at 50 and 100 fish/m3 (mean weight 336g and 293g respectively) were significantly larger than fish stocked at 200/m3 (233g). Survival was 100, 98 and 91%, food conversion ratios 1.6, 1.5, and 1.6, production rates 16.8, 29.2 and 42.5kg/m3, and absolute growth rate 1.3, 1.4 and 0.9g/day at densities of 50,100 and 200 fish/m3 respectively.

 

(ii) Fingerling experiment. Small fingerlings (4g) were stocked into 12 tanks at densities of 250, 500, 1000 and 1500 fish/m3 and cultured for 124 days (4 months) from April to July. Each treatment had three replicate tanks and fish were sampled monthly. Temperature was maintained at 240C. Fish were fed a formulated diet containing 52% protein to satiation twice daily. After 124 days, mean weights were 67.9, 55.1, 48.5, and 42.7g at densities of 250, 500, 1,000 and 1,500 fish/m3 respectively. Survival was high  (> 95%) in all tanks. Food conversion ratios were 0.9, 1.0, 1.0 and 0.8, production rates of 16.8, 26.5, 47.8 and 63.45kg/m3, and absolute growth rates 0.5, 0.4, 0.4 and 0.3 g/day at densities 250, 500, 1,000 and 1,500 fish/m3 respectively.

 

SUMMARY

 

Silver perch are capable of handling crowded conditions in RAS; however, in both experiments there were infestations of parasites (gill flukes and Ichtyobodo sp.) and a high level of management was required to operate the RAS. Formalin and trichlorfon were used to control infestations. Towards the end of the grow-out experiment, fish lost their appetite, growth slowed and frayed tails were common.

 

Over-wintered fingerlings performed very well and growth far exceeded that of fish in ponds and cages during winter.

 

These results demonstrate that large fingerlings can be produced over winter in well- designed RAS. Production time to market-size could be considerably shortened by stocking “advanced” and graded fingerlings in early spring.