No abstract

The aim of the present investigation was to evaluate the effect of carvacrol, administered with feed, on growth, haematology and survival tambaqui, Colossoma macropomum, infected by Aeromonas hydrophila exposed to hypoxia. Carvacrol was incorporated into fish feed at the following concentrations: 0 (control), 10, 20 and 40 g.kg−1 for 60 days. Fish fed 10 g.kg−1 of carvacrol‐enriched diet had an increase in final weight (72.68 ± 1.63) and specific growth rate (1.89 ± 0.03) and a decrease in apparent feed conversion compared (1.65 ± 0.09) with the control group. In addition, the condition factor (2.03 ± 0.04) and weight gain (49.31 ± 1.54) were also improved in animals fed 10 g.kg−1with carvacrol. RBC count, MCV, mean MCHC, LG‐PAS+, thrombocytes and lymphocytes presented no differences between treatments; however, Ht (25.6 ± 1.20) and mean MCV (224.05 ± 9.64) of the animals fed the highest carvacrol level were lower than the control animals, suggesting microcytic anaemia. Increased monocytes (6.54 ± 1.07), neutrophils (9.14 ± 0.57) and phagocytic activity (32.77%) were recorded in animals fed 10 g.kg−1 with carvacrol, in relation to the control. Glucose, cholesterol and albumin presented no changes; however, lower triglyceride values were observed in animals fed 40 g.kg−1 carvacrol‐enriched diet. Animals fed 10 g.kg−1 of carvacrol had higher plasma protein (3.31 ± 0.05) and globulin (1.97 ± 0.06) concentrations and a higher survival rate when submitted to bacterial infection. Thus, carvacrol‐enriched diet improves C. macropomum growth, haemato‐immune system, metabolism and resistance to A. hydrophila infection.

Colossoma macropomum, known locally as tambaqui, is the native fish most farmed in Brazil, however, technological advances are needed to reach efficient production rates. Modulating growth factors, such as growth hormone, may be associated with improved growth rate and feed efficiency. The use of exogenous hormone for fish rearing is prohibited in Brazil, yet the experimental use of bovine hormone can be useful in research aimed at understanding how to stimulate endogenous growth hormones in fish. Therefore, the present study had the strict objective of understanding the effects of growth hormone on the physiology and zootechnical parameters of C. macropomum under experimental conditions. The animals were intraperitoneally injected every fifteen days with 1, 10 and 100 μg g-1 of bGH using 0.9% NaCl saline as diluent. The 10 and 100 μg g-1 bolus had a positive effect on the performance indexes of C. macropomum: weight gain (g), growing length (cm), daily weight gain (g), feed conversion and specific growth rate (% per day). The bGH promoted a greater increase in length than in mass, which caused a reduction in condition factor of the individuals receiving a bolus of 10 and 100 μg g-1. Furthermore, bGH caused no changes in glucose levels, cortisol, hematological parameters, plasma levels of Na+ and K+, and activity of gill’s H+-ATPase and Na+, K+-ATPase, at least during the experimental period considered in the present study.

The objective of this study was to evaluate the efficiency of food deprivation on the growth performance of the commercially important hybrid fish tambacu (Piaractus mesopotamicus male × Colossoma macropomum female). For this, 171 juveniles of average length 8 cm and 11.4 g body mass were distributed in nine tanks, and allocated to three treatments: the fish were fed every day (control), fed for six days followed by one day of food deprivation (6F/1D) and fed for five days followed by two days of food deprivation (5F/2D). After 77 days, all animals achieved similar growth rates. Only animals submitted to two days of food deprivation presented hyperphagia. There was a reduction in total feed consumption of 3.8% and 10.8% for the 6F/1D and 5F/2D treatments, respectively. Our results suggest that juvenile tambacu exhibit total compensatory growth when submitted to food deprivation, and that a two-day deprivation could significantly reduce production costs for tambacu farmers.