Abstract
Abstract: The objective of this work was to evaluate the effect of stocking density associated with the swimming exercise on the stress responses of Brycon amazonicus. During 70 days, fish were subjected to three stocking densities: LD, low density of 88 fish per cubic meter; ID, intermediary density of 176 fish per cubic meter; and HD, high density of 353 fish per cubic meter. These densities were combined with static water (non-exercised group) or moderate-speed water (exercised group). Chronic stress was observed in HD, and plasma cortisol and glucose increased with the stocking densities. In HD, levels of plasma cortisol were significantly lower in exercised fish (135 ng mL-1) than in non-exercised ones (153 ng mL-1). The greatest hepatic glycogen bulks occurred in fish kept in ID and sustained swimming. Hepatic free amino acids (FAA) increased with the stocking density, particularly in non-exercised fish. The contents of FAA in the liver and of free fatty acids (FFA) in the liver and muscle were mobilized to meet the metabolic demands imposed by exercise and stocking density. The hematological parameters remained stable. The results show that Brycon amazonicus is more resistant to stress when subjected to sustained swimming and high stocking density than to static water.
Highlights
Aquaculture is growing at a rate of 5.8% a year as consequence of a series of combined factors, such as human population growth, rising incomes, and urbanization, which require high-quality healthy products (FAO, 2016)
Rearing of B. amazonicus under sustained swimming attenuated the stress caused by crowding; plasma cortisol was increased in HD even in fish adapted to the exercise (Figure 1 A)
The best response was observed in fish subjected to HD and static water, which showed cortisol levels that surpassed in 11.89% those of fish under HD and exercise
Summary
Aquaculture is growing at a rate of 5.8% a year as consequence of a series of combined factors, such as human population growth, rising incomes, and urbanization, which require high-quality healthy products (FAO, 2016). To reach high profits, fish farmers tend to overstock, ignoring the species demands, which increases the competition for space and contributes to environmental deterioration. High stocking rates may cause environmental impacts, Pesq. Reduced water quality, and the increase of toxicants as ammonia (Björnsson & Ólafsdóttir, 2006). These factors impair fish growth, health, and hematological parameters, increasing pathological conditions and leading to their death (Fazio et al, 2014)
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