ABSTRACT The chemical composition of diets is appointed as one responsible by different results of L-carnitine supplementation in fish. This study determined the effects of digestible dietary protein (DP; 250 and 290 g kg-1) and crude fat (CF; 100 and 150 g kg-1) at levels of DL-carnitine supplementation (DLC; 0 and 1.0 g kg-1) in plant based-diets on growth and whole-body composition of Nile tilapia Oreochromis niloticus fingerlings (1.55 ± 0.03 g). Fish were hand-fed for 74 days, three times per day until apparent satiation, in a completely randomized experimental design, 2×2×2 factorial scheme (n = 3). There was no effect (P > 0.05) of DP, CF, and DLC, or interactions, on growth performance. There was a significant interaction between DP×CF; DP×DLC and DLC×CF on feed efficiency. There was interaction (P < 0.05) between CF×DLC on feed intake (DFI). The DLC supplementation in 100 g kg-1 CF diets increased DFI 5.6% more than fish fed with the same fat level without DLC. Whole-body protein decreased significantly due to DLC supplementation in fish fed with 150 g kg-1 CF diets. The level of DLC supplementation in Nile tilapia diets is variable and should consider the dietary CF levels, but not DP.

Abstract Diet supplementation with essential oil from sweet basil Ocimum basilicum (EOOB) can increase fish growth. So, this study aimed to evaluate the effect of EOOB in the diet on growth performance and plasmatic variables of pirarucu juveniles (Arapaima gigas) submitted to stressful condition (stocking density of 7.56 kg m-3per tank and limited space). Four diets (in triplicates) were evaluated with increasing levels of EOOB (0.0 control; 0.5; 1.0; and 2.0 mL kg diet-1) over 48 days. Linalool was the major constituent of EOOB (54.19%). The addition of 2.0 mL EOOB kg diet-1 improved final weight, weight gain, specific growth rate, condition factor and feed conversion ratio; it also decreased plasma urea levels and increased plasma albumin and total proteins levels. Plasma glucose, cortisol, and acid uric levels were not influenced by the addition of EOOB to the fish diet. In conclusion, the addition of 2.0 mL EOOBkg diet-1 is recommended for pirarucu juveniles, due to improved growth performance, and this supplementation did not compromise the homeostasis of fish rearing in a high stocking density.

Abstract Although fish may live in different aquatic environments, variations in the water quality parameters, mainly pH, may have a substantial impact in their development and welfare. The objective of this study was to test the effect of different pH levels on the growth performance and biochemical variables in Amazon catfish juveniles (Pseudoplatystoma reticulatum x Leiarius marmoratus). Fish were subjected to four different water pH levels (4.56, 6.0, 7.24, and 8.90) for 40 days. The total ammonia and alkalinity were higher and lower, respectively, in the treatments with water pHs 4.56 and 6.00 than at the other water pH levels. The un-ionized ammonia was higher at water pH 8.90 than at the other water pH levels. Amazon catfish exposed to water pH 4.56 presented specific growth rate and weight gain significantly higher than other water pH values. In general, fish under exposure to water pH 8.90 presented lower growth performance than other water pH values. Biochemical changes were recorded at all water pH. In conclusion, water pH 4.56 is recommended for an Amazon catfish production system, since fish presented higher growth and water quality variables were kept within adequate limits for aquaculture.