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Generally, energy expenditure and compensation according to food deprivation and refeeding often occur along the life cycle of farmed-raised fish. Fasting and refeeding are also hypothesised to modulate carbohydrate metabolism particularly for herbivorous and/or omnivorous. This study aims to investigate the effects of short-term fasting and subsequent refeeding with high or low−carbohydrate diets on the intermediary carbohydrate metabolism of juvenile and adult Nile tilapia (Oreochromis niloticus) which is known to be a good user of carbohydrate as an energy source. Fish were fasted for 4 days and subsequently refed with either a low carbohydrate and high protein (LC/HP) or high carbohydrate and low protein (HC/LP) diet for 4 days. Our results showed that 4 days of refeeding with either one of the diets could compensate for weight loss due to fasting. Thus, we investigated the effects of a 4-day-refeeding strategy and different carbohydrate−refeeding diets on plasma metabolites, nutrient composition, and glucose and its related metabolism in the liver and muscle of adult fish. Refeeding had similar effects in adults and juveniles and induced modulations to the intermediary metabolism: (1) refeeding with the HC/LP diet elevated plasma glucose levels; (2) refeeding with both diets increased triglyceride levels in the plasma, liver, and muscle, but the effect of the HC/LP diet was superior; (3) refeeding elevated plasma cholesterol levels in adults, irrespective of diet; (4) refeeding with both diets increased hepatic lipid levels in juveniles, with stronger effects observed in those fed the HC/LP diet, and refeeding with the HC/LP diet elevated hepatic lipid levels in adults; (5) refeeding with both diets increased the plasma protein content, but the effect of the LC/HP diet was superior; (6) refeeding with the LC/HP diet increased hepatic protein content in adults; and (7) refeeding with both diets increased hepatic glycogen levels, but the effect of the HC/LP diet was superior. Additionally, in juveniles and adults, refeeding with the HC/LP diet upregulated the expression of glycolytic genes in the liver and muscle, lipogenic genes in the liver, and glucose transport genes. Moreover, refeeding with the HC/LP diet downregulated the expression of gluconeogenic and amino acid catabolism genes in the liver and amino acid catabolism genes in the muscle. Collectively, the effect of short-term refeeding with a high carbohydrate diet on intermediary metabolism resembled that of long-term feeding, supporting the hypothesis that Nile tilapia, an omnivorous fish, is highly responsive to dietary carbohydrates.

Generally, energy expenditure and compensation according to food deprivation and refeeding often occur along the life cycle of farmed-raised fish. Fasting and refeeding are also hypothesised to modulate carbohydrate metabolism particularly for herbivorous and/or omnivorous. This study aims to investigate the effects of short-term fasting and subsequent refeeding with high or low-carbohydrate diets on the intermediary carbohydrate metabolism of juvenile and adult Nile tilapia (Oreochromis niloticus) which is known to be a good user of carbohydrate as an energy source. Fish were fasted for 4 days and subsequently refed with either a low carbohydrate and high protein (LC/HP) or high carbohydrate and low protein (HC/LP) diet for 4 days. Our results showed that 4 days of refeeding with either one of the diets could compensate for weight loss due to fasting. Thus, we investigated the effects of a 4-day-refeeding strategy and different carbohydrate-refeeding diets on plasma metabolites, nutrient composition, and glucose and its related metabolism in the liver and muscle of adult fish. Refeeding had similar effects in adults and juveniles and induced modulations to the intermediary metabolism: (1) refeeding with the HC/LP diet elevated plasma glucose levels; (2) refeeding with both diets increased triglyceride levels in the plasma, liver, and muscle, but the effect of the HC/LP diet was superior; (3) refeeding elevated plasma cholesterol levels in adults, irrespective of diet; (4) refeeding with both diets increased hepatic lipid levels in juveniles, with stronger effects observed in those fed the HC/LP diet, and refeeding with the HC/LP diet elevated hepatic lipid levels in adults; (5) refeeding with both diets increased the plasma protein content, but the effect of the LC/HP diet was superior; (6) refeeding with the LC/HP diet increased hepatic protein content in adults; and (7) refeeding with both diets increased hepatic glycogen levels, but the effect of the HC/LP diet was superior. Additionally, in juveniles and adults, refeeding with the HC/LP diet upregulated the expression of glycolytic genes in the liver and muscle, lipogenic genes in the liver, and glucose transport genes. Moreover, refeeding with the HC/LP diet downregulated the expression of gluconeogenic and amino acid catabolism genes in the liver and amino acid catabolism genes in the muscle. Collectively, the effect of short-term refeeding with a high carbohydrate diet on intermediary metabolism resembled that of long-term feeding, supporting the hypothesis that Nile tilapia, an omnivorous fish, is highly responsive to dietary carbohydrates., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Cryopreservation of spermatogonia could be a useful tool to preserve the genetic resources of fish, which could be further restored via germ cell transplantation. In this study, the protocol for the cryopreservation of the spermatogonia of Asian sea bass (Lates calcarifer), an economically important fishery resource in the Indo-West Pacific, was optimised. The impact of the cryopreservation technique on cell viability and apoptosis, expression of several genes related to immature germ cell markers, transplantability in allogeneic recipients, and global DNA methylation was evaluated. The slow-freezing method was performed for the cryopreservation of immature testis tissue, which contains a high proportion of spermatogonia. The optimal condition that yielded the highest recovery rate of post-thawed spermatogonia included a cryomedium containing Leibovitz's (L-15) medium and 10 % dimethyl sulfoxide, ice equilibration for 60 min before freezing, and subsequent thawing at 4 °C for 8 min. Moreover, a higher number of early and late apoptotic cells was detected in the cryopreserved than in the fresh testes, suggesting that apoptosis could result in reduced viability. The expression levels of dazl decreased in the cryopreserved testes; however, there were no significant differences in the expression levels of nanos2 or nanos3 between the fresh and cryopreserved testes. Although qRT-PCR showed lower vasa expression in cryopreserved testicular cells, in situ hybridisation showed expressed vasa in the cryopreserved testicular cells. Post-thawed spermatogonia could be incorporated into the genital ridge of allogeneic recipients, suggesting that cryopreserved spermatogonia exhibit transplantability characteristics. Compared with fresh testes, significant changes in the proportion of DNA methylation (decreased 5-mC and 5-caC) were observed in cryomedium-free testicular cells, whereas those of the cryopreserved cells were not significantly different. Therefore, the method we developed for the cryopreservation of the spermatogonia of Asian sea bass enabled post-thaw cells to retain several stemness characteristics and maintain their epigenetic stability., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)