The Brazilian sardine is the most important fishery resource in Brazil. Their production has declined along the last 30 years due the overfishing, climatic and oceanographic phenomena. This study was carried out to determine the optimal feeding frequency for juvenile Brazilian sardine based on growth, feed efficiency, feed intake and body composition. Six feeding frequencies of one, two, three, four, five and six times a day were evaluated in triplicate tanks for 50 days. Fish with initial mean weight of 3.29 AE 0.56 g were fed daily to apparent satiation. The results showed that fish fed once daily had lower body weight gain, specific growth rate and condition factor (P < 0.05) compared with other treatments. The feed efficiency ratio in fish fed once daily was significantly higher (P < 0.05) than those fed two or more times a day. No significant differences were observed in the coefficient of variation in body weight (P > 0.05) among the treatments. Feed intake was directly proportional to the feeding frequency. Fish fed once daily showed lower hepatosomatic and mesenteric fat indices (P < 0.05) than the other treatments. Neither protein nor ash content of fish were significantly (P > 0.05) affected by feeding frequency. However, the lipid content increased with feeding frequency. The results suggest that the optimal feeding frequency for juvenile Brazilian sardine is at least twice daily.
A 6-week growth trial was conducted to evaluate the effects of feeding rate on growth performance, body composition, plasma metabolites and enzyme activities, and to determine the optimal feeding rate for juvenile Brazilian sardine. Fish were fed at six feeding rates, 2, 4, 6, 8, 10% BWday −1 (body weight per day) and until satiation (10.3% BWday −1 ). The survival of fish fed at 2%-6%BWday −1 was significantly higher (p < .05) than the survival of fish fed at the other feeding rates. The final body weight and specific growth rate significantly increased (p < .05) with increasing feeding rates while feed utilization decreased. Total proteins, cholesterol and triglycerides concentrations increased significantly with increasing feeding rates; however, there was no significant effect on glucose levels. Body protein and ash contents were not affected by the feeding rates. Whole-body lipid content increased significantly as the feeding rate increased, while moisture content had an opposite trend. Proteases and amylase activities significantly decreased with increasing feeding rates, while lipase activity was not influenced by the feeding rate. Our results suggest that low feeding rates stimulate mobilization of metabolites to supply energy for the maintenance of overall metabolism and digestive enzyme activities increase to enhance feed utilization. The optimum feeding rate of juvenile Brazilian sardine based on PRR as determined by the second-order polynomial regression was 5.45% BWday −1 . K E Y W O R D Sbody composition, brazilian sardine, digestive enzymes, feeding strategy, fish nutrition, plasma metabolites
The common snook, Centropomus undecimalis, is an emerging species for intensive fish culture, however, some reproductive aspects of this species, especially the development of the testes and the action of androgen hormones on spermatogenesis have not been studied. The objective of this study was to evaluate the effects of 17α-methyltestosterone (MT) on spermatogenesis and steroidogenesis during the first sexual maturation of the common snook. The fish, which were reproduced in captivity, had a body weight of 305.80 ± 35.60 g and a total length of 34,11 ± 1,08 cm. We used ethylene-vinyl-acetate (EVAc) implants with four concentrations of the hormone MT: T1 (0.3 mg/kg); T2 (3.0 mg/kg); T3 (15.0 mg/kg) and T4 (30.0 mg/kg), and a control group that did not receive the hormone. The gonads increased (P < 0.05) in relation to the concentrations of MT. Histological analysis revealed a progression of spermatogenesis in the MT treatments, especially in T3 and T4. Sperm release was attained in some fish treated with MT. However, there was a partial suppression of the levels of testosterone (T) and 11-ketotestosterone (11-KT) in plasma in the MT treatments, indicating a negative feedback on steroidogenesis. However, this suppression of T and 11-KT in plasma did not prevent an increase in the gonadosomatic index and the progression of gametogenesis. There was also an increase of estradiol (E2) in plasma in the treatments with the highest MT concentrations. The results suggest that the application of EVAc implants with MT at concentrations of 15 and 30 mg/kg stimulates the development and growth of the testes and accelerates spermatogenesis.
The common snook (Centropomus undecimalis) is a protandric hermaphrodite fish that has potential for aquaculture due to its high value and market acceptance. One of the difficulties to its reproduction in captivity is that females are older and bigger than males. The objective of this study was to use 17-b oestradiol (E2) hormone implants to induce sex inversion in adult males. Fish with an initial body weight of 383 AE 83 g (mean AE SD), individually tagged were used in the experiment. Four E2 dosages (n = 7) were tested (0.5, 1.0, 4.0 and 8.0 mg kg À1 ) in Ethylene-vinyl-acetate (EVAc) implants, and a control group (n = 7) implanted without hormone. The parameters evaluated were: survival, weight gain, hepatosomatic and gonadosomatic indices (GSI and HSI) and plasma levels of testosterone (T) and 17-b oestradiol (E2). Also, liver and gonad morphology was observed through histological sections. GSI was higher in E2 treated than in control fish. All E2 treated fish had completely developed ovaries with oocytes at the perinucleolar stage, while all fish in the control group remained males with evidence of active spermatogenesis. After 15 days, plasma levels of E2 were correlated with the hormone dosage. T levels in the control group were higher than in E2 treated fish, at all sampling times. In conclusion, 0.5 mg kg À1 of E2 in EVAc implants is effective to induce sexual inversion in common snook males, which could be useful to obtain broodstock females smaller than in the wild in a reduced time.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.