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Triplicate groups of rainbow trout (Oncorhynchus mykiss) (1.4 ± 0.1 g) were fed experimental diets containing four levels of protein substitution to totally replace fishmeal with poultry by‐product meal (0, 33, 67 and 100%). Fishmeal (FM) from tuna fish by‐products and poultry by‐product meal ‘pet food grade' (PBM) were used. Diets were formulated to be isonitrogenous (43.5% crude protein) and isolipidic (12.5% crude fat). After 80 days of feeding, no significant differences were found in terms of thermal unit growth coefficient (TGC). However, the EPA levels in muscle tissue among treatments 0PBM, 24PBM and 44PBM were found to be significantly higher than those for the 59PBM diet. Nevertheless, a re‐feeding period with the control diet showed that 28 days was long enough to regain the FA profile needed. We concluded that PBM used up to 44% in diets for juvenile rainbow trout can be used without a significantly decrease in EPA and DHA under the present conditions. The use of a whole fishmeal diet could be an important strategy to recuperate the fatty acid profile obtained when trout is feed on PBM basis. It will be important to perform longer experiments with larger fish to confirm these results.

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Growth, ammonium excretion, and oxygen consumption of hybrid red tilapia (Oreochromis mossambicus × Oreochromis aureus) grown in seawater and freshwaterCrecimiento, excreción de amonio y consumo de oxígeno de la tilapia híbrida roja (Oreochromis mossambicus × Oreochromis aureus) cultivada en agua de mar y en agua dulce ABSTRACT. In a comparative study using the hybrid tilapia Oreochromis mossambicus × Oreochromis aureus grown in seawater and freshwater, no significant differences in growth performance (weight gain) and biological indices (e.g., feed conversion efficiency and survival) was observed after 90 days of experimentation. A common feed was formulated to contain 40% crude protein and 8.5% crude fat. Fish meal and poultry by-product meal (50:50) were used as a source of protein in the formulation. The study was conducted using recirculation systems and organisms already adapted to seawater and freshwater with an initial weight of 25.0 ± 0.06 g and 24.70 ± 0.32 g, respectively (four replicates per treatment); at the end of the experiment their final weight was 161.80 ± 12.78 g and 167.60 ± 7.29 g, respectively. The thermal growth coefficient was 0.91 and 0.89 (seawater vs freshwater), and there were no significant differences; however, the apparent digestibility of dry matter as well as per nutrient (protein, lipid, and carbohydrate) was significantly higher for the organisms in the seawater treatment. The digestibility could be associated with greater enzymatic activity in the presence of higher ionic strength. The respirometric study indicated that the O:N ratios were similar for organisms reared in seawater and freshwater, with values of 21 and 18, respectively. This indicates that this strain of tilapia uses a mixture of proteins and lipids as energy substrates. We conclude that this strain of tilapia has the potential to adapt and thrive in a marine environment and that its production practices could be expanded.Key words: hybrid tilapia, seawater, growth, O:N ratio, metabolic substrate. RESUMEN.En un estudio comparativo en el cual se utilizó el híbrido de tilapia Oreochromis mossambicus × Oreochromis aureus cultivado en agua de mar y en agua dulce no se observaron diferencias significativas en el desempeño como crecimiento en peso e índices biológicos (e.g., conversión alimenticia y supervivencia) después de 90 días de experimentación. Se utilizó un alimento común elaborado en el laboratorio que contenía 40% de proteína cruda y 8.5% de grasa cruda. Para la formulación del alimento, se utilizó harina de pescado y harina de subproducto de ave (50:50) como fuente de proteína. El estudio se realizó utilizando sistemas de recirculación y organismos de 25.0 ± 0.06 g y 24.70 ± 0.32 g para los tratamientos de agua de mar y agua dulce, respectivamente, con 4 repeticiones por tratamiento. Al finalizar el experimento los peces alcanzaron un peso de 161.80 ± 12.78 g y 167.60 ± 7.29 g, respectivamente. El coeficiente térmico de crecimiento fue de 0.91 y 0.89 (agua de mar vs agua dulce), y no se observaron diferen...

The fatty acid composition of juvenile green abalone (Haliotis fulgens) exposed to lipid restriction and long-term starvation was studied. Juvenile organisms were acclimated during 26 days and then randomly separated into three treatment groups. One group was fed a restricted diet containing low lipid content (0.14%), another was fed a rich diet containing the optimal lipid content (5.1%), and the third was kept under starvation conditions. After 90 days, the abalone fed the restricted diet showed a significant increase in 18:1n-9 content and a decrease in n-3 and n-6 polyunsaturated fatty acids (PUFA), but the total lipid level remained similar to that observed before the treatment, suggesting lipogenesis. On the other hand, no changes in total lipid content and fatty acid profile were found during the 90-day treatment using the rich lipid diet compared with the initial samples. Starved abalone showed that lipids did not constitute the main energy source and that the concentrations of long-chain PUFA did not change throughout the 90-day starvation period.