The present study evaluated different levels of the essential oil of Nectandra grandiflora (EONG) in the diet of juvenile Colossoma macropomum. The juveniles (0.75 ± 0.05 g) were fed four experimental diets with differing levels of EONG (0, 0.5, 0.75, and 1.50 mL/kg). After 20 days, the weight, daily weight gain, specific growth rate, and daily feed consumption per fish were highest for the fish fed 0.5 mL EONG/kg, while after 30 days, only the weight and daily feed consumption per fish for that diet remained highest. The viscerosomatic index was highest for the fish fed 0.5 mL EONG/kg while the hepatosomatic index was higher for the groups that received dietary EONG for 30 days. The juveniles fed 1.5 mL EONG/kg showed a proliferative response of the mucous cells in the gills, but the proliferation of these lysozyme- and immunoglobulin-secreting mucosal cells was higher for the skin of the fish of all EONG levels, compared to that of the control fish. The fish fed 0.5 mL EONG/kg had the greatest height and width of intestinal villi. The two highest levels of dietary EONG supplementation (0.75 and 1.50 mL/kg) reduced the hepatocyte dimensions but did not modify the centrolobular vein area. Dietary supplementation with 0.5 mL EONG/kg improved the growth, gut health, and immune response of juvenile C. macropomum.

Objective. The study evaluated the performance and survival of Colossoma macropomum larvae at different temperatures and concentrations of prey. Materials and methods. Two temperatures (28 and 32ºC) (T) and two initial daily concentrations (500 and 1,000 Artemia nauplii per larva) (CP) of prey were used. These concentrations were increased every 5 days during the first 15 days of cultivation. From the 16th to the 30th day, the larvae received exclusively a commercial diet. Results. In the first 7 days, weight (P), total length (TL) and daily specific growth rate (SGR) were higher for T32 treatments (p<0.05). After 15 days, P, TL and SGR were higher for CP1000 (p<0.05). After 22 days, P and TL suffered the effect of the initial concentration of prey and water temperature with higher values for CP1000 and T32 (p<0.05). At the end of 30 days of cultivation, P was affected only by water temperature with higher values for T32 (p<0.05). The TL showed an effect of temperature and initial concentration of prey with higher values for CP1000 and T32 (p<0.05). During feeding with a commercial diet (days 16-30 of cultivation), survival was higher for T32 (94.38±6.12%) (p<0.05), with no difference for initial prey concentration. Conclusions. It is concluded that the larviculture of C. macropomum must be carried out with a temperature of 32° C and that the food management must be differentiated during the first 15 days, positively influenced in the period of feeding with ration.

Biochemical parameters of fish are important indicators of homeostasis as they represent an organism's response to the environment. Lophiosilurus alexandri is an endemic and endangered species of the São Francisco River in Brazil with potential for aquaculture; however, blood biochemical studies of this species are scarce. The present study compared blood biochemical parameters of male and female L. alexandri, at four different ages. The following analytes were evaluated: alanine aminotransferase (ALT), aspartate transaminase (AST), lactate dehydrogenase (LDH), calcium, chlorine, magnesium, total proteins, albumin, urea, glucose, triglycerides and cholesterol. Male fish had higher values than females for ALT at 372 days after hatching (DAH), magnesium at 481 DAH and triglycerides at 372 and 481 DAH (p < 0.05). The other analytes did not differ significantly (p > 0.05) between males and females at any of the collection times. The results allow us to conclude that biochemical differences between males and females are less pronounced than those observed among different ages of the same sex.

This work aimed to evaluate two types of substrate for egg production by annual killifish (Hypsolebias flagellatus) and to describe the reproductive behaviour of males and females. Experiment I, with two phases, tested two types of substrates: coconut shell powder (CP) and brown 100% acrylic wool (AW), with five male–female pairs in each treatment. In Phase 1, reproduction was monitored for 45 days. In Phase 2, AW nests were replaced by CP nests and reproduction monitored for another 45 days. Experiment II, with three phases, involved installing a camera and inserting a CP nest in each of five aquariums with one pair in each. Phase 1 began after 5 days of adaptation and involved observing the pairs for 4 days. Phase 2 began on the fifth day with the removal of nests followed by observation for 48 h. In Phase 3, the nests were returned and the pairs were observed for another 4 days. Phase 1 of Experiment I found higher egg production with CP substrate (p < 0.05). In Phase 2, egg production did not differ significantly between treatments (p > 0.05) after AW substrate was replaced by CP. Phase 2 of Experiment II found almost no interaction between the sexes. Both sexes spending most of their time close to the nest (p < 0.05). The frequency of nest entry and exit was higher for males than for females in both Phase 1 and Phase 3 (p < 0.05). The CP substrate showed better results for the reproduction of H. flagellatus than did the AW substrate.