Optimizing intensive culture protocols for Atlantic cod (Gadus morhua) larvae

Abstract

Larval cod require live prey as food, and prey concentration (PC) and feeding frequency (FF) often afect their growth and survival. Apart from this, water exchange rates/water fow (WER/WF) and water current (WC) also afect the prey resident time in the tank and larval/early juvenile behaviour, respectively. High water current is also known to induce stress in fnfsh larvae, and this stress response is believed to be dependent on larval developmental stage. Thus, we conducted a study to evaluate three larval rearing protocols varying in prey concentration, feeding frequency, and water current/exchange rate. Three protocols were used: low prey concentration (PC), low feeding frequency (FF), and low water fow (protocol 1); medium PC, medium FF, and medium WF (protocol 2); and high PC, high FF, and high WF (protocol 3) (see Table 1). Larvae were sampled periodically for growth and cortisol measurements. Cortisol extraction and radioimmunoassay (RIA) were conducted using methods previously validated for cod larvae. Larvae reared using protocols 2 and 3 were signifcantly bigger and heavier than larvae reared using protocol 1. Rearing protocol had a signifcant efect on the cortisol level in larval cod. Larvae showed a developmental stage-dependent stress response. Protocol 2 had signifcantly higher survival than protocols 1 and 3. Our results indicate that an intermediate PC, FF, and WF (protocol 2) is suitable during cod larval rearing.