ABSTRACT: Cobia is one of the most promising warm water aquaculture species. In Brazil, cobia farming began in 2008 in the state of Rio de Janeiro from experimental scale facilities to regular near-shore farms based on fresh/frozen fish diets composed mostly of Sardinella sp. Despite the encouraging results achieved in the promotion of sustainable cobia farming, we advocate the replacement of fresh/frozen fish by a practical formulated feed. This experiment evaluated the zootechnical performance and environmental efficiency of moist and practical formulated feeds in early grow-out phases in the cycle of cobia nearshore cage culture. Four hundred and twenty juvenile cobia (151 ± 7 g) were fed with moist feed and practical formulated feed for 56 days. Biometrics were taken every two weeks and diets were analyzed for proximate composition, fatty acid composition and pellet quality. Although growth performance was equivalent between treatments, feed consumption and feed conversion ratios (FCR) were different (p < 0.05) and varied according to water temperature. Cobia fed moist feed exhibited an FCR two times higher than those fed formulated feed. Elevated settling speed and low floatability contributed to higher heterogeneity and lower efficiency of fish fed moist diet. Nitrogen excretion rate was reduced (64 %) and protein efficiency ratio elevated (27 %) within formulated diet groups in comparison to those fed moist diet (79 % and 15 %, respectively). The fatty acid profile of cobia muscle was similar across the groups. With no negative effects of diet substitution on production performance and improvement of environmental efficiency, this approach can be applied and advocated globally and contribute to the responsible intensification of sustainable marine fish culture.

The objective of the present study was to evaluate the protein requirement of juvenile Trichogaster lalius, blue variety. The experimental design was of randomised blocks (B1 = initial weight of 1.04±0.05 g and B2 = 1.36±0.02 g), with two replicates within each block and five treatments (230, 270, 310, 350 and 390 g CP/kg diet). The fish were fed to satiation, three times a day for 90 days. The study evaluated: survival rate, weight gain, final length, feed intake, feed conversion ratio, protein efficiency ratio, specific growth rate and condition factor. There was a linear effect of dietary protein levels for protein efficiency ratio, specific growth rate (positive linear effect) and feed conversion ratio (negative linear effect). For weight gain, final length, feed intake and condition factor a quadratic effect of dietary protein levels was observed, with estimated values of 409.8, 366.2, 317.4 and 365.0 g CP/kg diet, to improve their performance parameters. Analysis of growth based on the length of the fish shows that 366.2 g of CP/kg diet meets the protein requirement of juvenile Trichogaster lalius, blue variety.

The study evaluated the replacement of bovine heart by gelatin in the feed training of carnivorous fish, using giant trahira (Hoplias lacerdae) as an experimental model. A completely randomized design with four treatments and five repetitions was employed. The treatments were composed of wet ingredients beef heart (control), gelatin diluted in water, gelatin diluted in beef heart broth, and gelatin diluted in water mixed with fish meal. The fish (3.22±0.03 cm and 0.57±0.01 g) were conditioned to accept industrialized diets by the technique of gradual feed ingredients transition in the diet. Gains in weight and length, efficiency of feed training, specific growth rate, cannibalism, mortality and survival rates were evaluated. There was significant difference in weight and length gains and specific growth rate, whereby the use of bovine heart gave the best results. Greater efficiency of feed training was observed for fish fed diets containing beef heart and gelatin diluted in water mixed with fish meal. The high survival rates and the absence of significant differences among treatments for rates of cannibalism, mortality and survival indicate the feasibility of using gelatin as a moist ingredient in the feed training of carnivorous fish.

The objective of this study was to investigate the effect of different water salinities on juvenile Hoplias lacerdae during feed training. Salinity levels of 0, 3, 6 and 9 g salt L-1 were used. Juveniles (3.33±0.1 cm and 0.6±0.09 g) were stocked at a density of six fish L-1 in aquaria (10 L volume) with supplementary aeration. Weight gain, length gain, and rates of survival, mortality, and cannibalism were evaluated after 20 days. Total mortality was observed in 0 g of salt L-1. The best survival rates of 98.7 and 97.5% were recorded in 3 and 6 g of salt L-1, respectively. The greatest weight gain was recorded in fish grown in 3 g of salt L-1 followed by fish grown in 6 g of salt L-1. Length gain was similar in the 3 and 6 g salt L-1 groups. No weight or length gain was recorded in 9 g of salt L-1. According to regression equations, the optimum water salinity was 5.15, 4.03 and 4.55 g of salt L-1 for survival rate, weight, and length gain, respectively. Salinity between 4.03 and 5.15 g of salt L-1 during feed training of juvenile giant trahira improves productive performance.