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Fish meal (FM) has long been considered an essential ingredient for the formulation of shrimp feeds. Until recently, 12%FM was considered a minimum amount, below which weight gain would become reduced due to a reduction in feed intake. In order to test this perceived minimum value, an experiment was conducted on a long-term basis with 4 replicates. Four practical isonitrogenous and isoenergetic diets were formulated for Litopenaeus vannamei juveniles. Survival, weight gain, feed conversion ratio (FCR) and protein efficiency ratio were determined for 0, 6, 10 and 15% FM diets and a reference diet. Shrimp survival ranged from 84 to 86.5%. Shrimp fed a diet with 0% FM showed lower average weight and SGR compared to the other treatments (P < 0.05). FCR of shrimp fed the reference diet was significantly lower compared to the other treatments. Short-term energy budget did not differ in recovered energy (RE). Variations in RE according to FM level were expected, however, it remained low (0.12 kJ prawn − 1 day − 1) and it was not possible to discriminate among dietary treatments. Data indicate that RE was similar as evidenced by an absence of difference in weight gain among 6, 10 and 15% FM diets and the reference diet (0.98 g/wk). Growth results obtained over a long-term period and in clear water indicated the possibility for FM replacement with soybean plus canola meals.

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As has been demonstrated in previous studies, Octopus maya can be fed on artificial diets. In the present study six different diets were assayed. Five diets were designed to test the effect of percentage of inclusion of fish protein concentrate (CPSP: 0, 5, 10, 15, and 20%) and were offered to octopuses as a specifically designed artificial diet. The sixth diet consisted of frozen crab (Callinectes spp) and was used as control diet. Blood metabolites and energy budget of octopuses were evaluated to determine how CPSP levels modulate the digestive capacity and allow retaining energy for growth. Wild animals (316.4 ± 9.8 g) were used in the study. Results showed that CPSP produced a positive specific growth rate (SGR, % day− 1) with high value in octopuses fed 15% CPSP level. A maximum growth rate of 0.86% day− 1 was recorded in these animals, a value that is extremely low when compared with the SGR obtained when animals were fed fresh crab (3.7% day− 1). In general, blood metabolites were affected by diet composition, indicating that some metabolites could reflect the nutritional and/or physiological status of octopus. Preliminary reference values for O. maya fed crab were found for glucose (0.09 ±0.02 mg/ml), lactate (0.004 ± 0.002 mg/ml), cholesterol (0.16 ± 0.02 mg/ml), acylglycerol (0.14 ± 0.01 mg/ml), protein (0.37 ± 0.04 mg/ml), hemocyanin (1.85 ± 0.04 mmol/l), and digestive gland glycogen (1.86 ± 0.3 mg/g). Total energy content can be used as an indicator of tissue metabolic reserves. In the present study, higher energy content in the digestive gland and muscle was observed in octopuses fed crab, followed by animals fed 15% CPSP. Results from the digestive gland indicated that the retained energy derived from glycogen, suggesting that lipids and protein were the main sources of variation linked with energy content. In general, digestive gland proteases activity and trypsin were induced in octopuses fed 15% CPSP. The capacity of O. maya juveniles to adjust their digestive enzymes to different types of food was evidenced. Essential amino acid content (EAA) of the diet was not a limiting factor. When dietary EAA profiles were compared with O. maya EAA profiles, all dietary EAA resulted in a higher concentration than whole body octopus composition. In the present study, all experimental groups ingested between 3300 and 4106 kJ wk− 1 kg− 1 without statistical differences among treatments, indicating that experimental diets were as attractive as crab. Differences were recorded in the proportion of absorbed energy (Ab, %) between CPSP-based and crab meat diets, suggesting digestion limitations associated with artificial diets. The present results indicate that the 15% CPSP diet had characteristics that stimulate digestive enzymes and reduce energetic costs associated with its digestion (HiE or SDA), channeling more biomass production than the other experimental diets.