No abstract

A 10‐week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fishmeal free diet. Three iso‐nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n‐3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n‐3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n‐3 HUFA and n‐6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n‐3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n‐3 HUFA content towards the same concentration of n‐3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores.

The first days of exogenous feeding are crucial for larval recruitment. A correct first prey item and the determination of the optimal weaning age, can reduce labor cost and fish mortality to a great extent. This study was conducted to evaluate the use of small and regular Artemia fransiscana (AF and EG Artemia, Inve, Belgium) as first feed for jade perch Scortum barcoo, and to determine the minimum required duration of this life feed phase before transition to dry feed can occur. Therefore, we compared first feeding of 3 days AF nauplii instar I with 3 days of EG nauplii instar I and evaluated whether the optimal weaning age for jade perch larvae was at 7, 10, 13 or 16 days post-hatching (DPH). The study was performed in 25-L tanks in a recirculating system and lasted for 21 days (4-24 DPH). Growth, survival and tissue fatty acid composition of the larvae in the different treatments were analyzed. Results indicate that, after the start of exogenous feeding at 4 days DPH, jade perch larvae require a minimum of 9 days of live feed until 12 DPH. Co-feeding ideally starts on 10 DPH. Larvae fed AF Artemia for the first 3 days showed a significantly faster growth than larvae fed EG Artemia, although their survival was lower. Gape width of larvae at 3 and 6 DPH was measured, and implications for prey size are discussed