Coping with suboptimal water temperature: modifications in blood parameters, body composition, and postingestive-driven diet selection in Nile tilapia fed two vegetable oil blends.

The world tilapia production faces seasonal variations. However, very few nutritional studies have addressed suboptimal temperature. We evaluated the effect of two temperatures (20 or 30 °C) and two vegetable oil blends (one rich in corn oil (COR) and one rich linseed oil (LIN)) on tilapia growth, body composition, and blood parameters using a 2×2 factorial design with the following treatments: COR-20; LIN-20; COR-30; LIN-30 (Trial 1). In addition, we also evaluated the effect of postingestive signals of dietary oils when the organoleptic properties of diets were isolated (Trial 2). In the Trial 1, 256 fish (15.36 ±â€¯0.14 g) were placed in 16 aquariums and submitted during 30 days to the 2×2 factorial designs: COR-20; LIN-20; COR-30; LIN-30. The temperatures were established in two independent water recirculation systems. In the Trial 2, 96 fish (34.02 ±â€¯0.79 g) were placed in 12 aquariums and subjected to the same experimental design of Trial 1, but to evaluate fish feeding behavior. They were allowed to select the encapsulated diets provided in different feeding halls to evaluate if diet preferences are influenced by postingestive signals. As the Trial 1 results show, diets had no significant effects on growth, dietary protein use, and body centesimal composition, but 30 °C induced the best performance and protein deposition (P < 0.05). LIN-20 showed lower very-low-density lipoprotein and cortisol, but higher high-density lipoprotein (HDL), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and triglycerides (TG) than COR-20 (P < 0.05). COR-30 presented higher HDL, AST, ALT, TG, and cortisol than LIN-30. The fish fed COR showed lower C20:5n-3 (EPA) and higher n-6 than fish fed LIN (P < 0.05). The fish fed LIN had high n-3 highly unsaturated fatty acid. ∑ polyunsaturated fatty acid was higher at 30 °C. Finally, the tilapia in Trial 2 showed clear diet intake regulation and preference for LIN (P < 0.05), regardless of temperature. In short, lipid sources had no influence on tilapia performance; however, temperature affects carcass lipid deposition as well as fatty acids profile. Notably, the preference for linseed oil can suggest nutritional metabolic issues, contributing to animal behavior knowledge.

Dietary self-selection of protein-unbalanced diets supplemented with three essential amino acids in Nile tilapia.

Animals do not eat whatever food item they encounter, but choose different foods that best match their requirements. Fish exhibit such "nutritional wisdom" and adapt their feeding behaviour and food intake according to their needs and the nutritional properties of diets. In this paper, we tested the ability of Nile tilapia to select between diets with a balanced or unbalanced composition of essential amino acids. To this end, three different diets were prepared: a gelatine based diet (D(1)), a gelatine diet supplemented with three essential amino acids (EAA, l-tryptophane, l-methionine, l-threonine) (D(2)), and a diet containing only cellulose and the three crystalline EAA (D(3)). In addition, the putative role of both orosensorial factors (using pellets vs capsules) and social interactions (single vs groups of ten fish) was investigated. To this end, a total of 68 male tilapia of about 141±48 g (mean±S.D.) were challenged, individually or in groups, to select between D(1)vs D(2) using pellets dispensed by self-feeders (exp. 1). In another experiment (exp. 2), 11 individual fish were challenged to select encapsulated diets with non flavour or smell proprieties (D(1)vs D(2)), and in exp. 3 fish were challenged to self-supplementation in EAA (D(1)vs D(3)). The results showed the ability of tilapia to avoid the EAA-deficient diet, choosing 82.2% D(2) in the case of individual fish, and 80.8% D(2) in the case of fish groups. Dietary selection was not directly driven by the orosensorial characteristics of food, since tilapia sustained a higher preference for D(2) when fed with encapsulated diets. Finally, in exp. 3 tilapia self-supplemented the EAA deficiency by selecting a synchronised combination of D(1) and D(3) that matched their nutritional requirements. These findings highlighted the capacity of fish to make dietary selection based on the EAA content, which should be considered when discussing food intake regulation mechanisms, and diet formulation and supplementation with EAA.

Macronutrient selection in Nile tilapia fed gelatin capsules and challenged with protein dilution/restriction.

Most animals, including fish, are known to possess "nutritional wisdom" which allows them to choose among different incomplete diets to self-compose a nutritionally balanced diet. The purpose of this research was to investigate dietary selection and the capacity of fish to associate between colour code of encapsulated diets and capsule contents. In addition, fish were subjected to different challenges (changing the relative position of capsules and their content, and protein dilution/restriction) to test whether tilapia defended a given intake target of macronutrients and energy. To help fish discriminate between diets, different relationships between capsule colour and content were used. The results revealed a clear pattern of selection: 45.4% P, 32.2% C, and 22.4% L. After diluting or restricting the protein, fish increased their intake of protein capsules to compensate for the dilution or restriction in such a way that their energy intake remained around 170 kJ/kg BW. These results confirm that tilapia, an omnivorous fish model, can select from individual macronutrients to self-compose a balanced diet, and are also able to regulate energy intake after protein dilution and selective protein deprivation. Besides, dietary selection and food intake regulation is not based on the oral properties of the diets because fish were fed tasteless gelatin capsules, suggesting that fish can associate the colour of the capsules with its nutritional effect.

Daily rhythms of locomotor activity, feeding behavior and dietary selection in Nile tilapia (Oreochromis niloticus).

Fish do not feed at any time of the day and on whatever food item they encounter in the wild, but they show daily rhythms of feeding activity and dietary selection. The aim of this research was to investigate the daily rhythms of behavior in Nile tilapia self-fed with plant-based diets supplemented with different levels of exogenous phytase (an enzyme that hydrolyzes non-digestible phytate and improves the nutritional value of the diet). To this end, ten males were individually kept in 50-L tanks, each equipped with two self-feeders and one infrared photo-cell connected to a computer. The selection factors investigated were the level of phytase supplementation (0 IU kg(-1) vs 1500 IU kg(-1); 1500 IU kg(-1) vs 4000 IU kg(-1)) or sodium phytate (1% phytate vs 1% phytate+1500 IU kg(-1) phytase). The results revealed that 66.7% of total daily activity occurred during the day, while feeding was strictly nocturnal, with 93.0% of the daily food demands occurring at night. Tilapia preferred the diet with 1500 IU kg(-1) phytase rather than the control or 4000 IU kg(-1) diets. When exogenous sodium phytate was added to the diet, tilapia preferred the phytase diet. In conclusion tilapia self-feed at night (although locomotor activity was mostly diurnal) and chose plant-diets containing phytase, which should be taken into account when designing feeding strategies and practical diets for tilapia aquaculture.