Abstract

Eleginops maclovinus is a native species with potential for Chilean aquaculture. However, its optimal stocking density and the impact on its physiology is unknown. The aim of this study is to determine the optimal stocking density range by evaluating parameters of growth, stress, intermediary metabolism, and osmoregulation. For this, 48 immature male fish (201.60 +/- 32 g; 29.05 +/- 1.45 cm) were randomly assigned to four stocking densities (3, 6, 12 and 24 kg/m(3)) and maintained for 60 days. No mortality was recorded, optimal growth was observed at a density of 3-6 kg/m(3) and decreased with a higher stocking density. In plasma, glucose and protein levels were not affected by stocking density, while triglycerides, lactate, total amino acids, cortisol, and osmolality showed a significant decrease at a higher stocking density. Enzymatic activity of branchial and renal NKA, in addition to water content in muscle, increased at a greater stocking density, while intestinal NKA showed non-significant differences. The metabolism of carbohydrates, triglycerides, and amino acids/protein in liver, gill, kidney, and muscle was significantly affected by stocking density and showed significant tissue-specific responses. Glycogen levels increased at a higher stocking density in gills, kidney, and muscle, suggesting that glucose plays an important role against chronic stress produced by stocking density. The GH/IGF-1 axis and HSP70 showed significantly lower levels of mRNA transcript at the high density of 24 kg/m(3). In conclusion, we suggest that stocking density affects the physiology of Eleginops maclovinus, activating the stress system and mobilizing energy substrates in a tissue-specific manner. Additionally, our data suggests that male E. maclovinus should be cultivated in the range of 3-12 kg/m(3), avoiding the high density of 24 kg/m(3).