Effects on the metabolism, growth, digestive capacity and osmoregulation of juvenile of Sub-Antarctic Notothenioid fish Eleginops maclovinus acclimated at different salinities

Abstract

In this study we assessed the influence of three different environmental salinities (5, 15 and 31 psu during 90 days) on growth, osmoregulation, energy metabolism and digestive capacity in juveniles of the Notothenioid fish Eleginops maclovinus. At the end of experimental time samples of plasma, liver, gill, intestine, kidney, skeletal muscle, stomach and pyloric caeca were obtained. Growth, weight gain, hepatosomatic index and specific growth rate increased at 15 and 31 psu and were lower at 5 psu salinity. Gill Na(+), K(+)-ATPase (NKA) activity presented a "U-shaped" relationship respect to salinity, with its minimum rates at 15 psu, while this activity correlated negatively with salinity at both anterior and posterior intestinal portions. No significant changes in NKA activity were observed in kidney or mid intestine. Large changes in plasma, metabolite levels and enzymatic activities related to energy metabolism in liver, gill, intestine, kidney and muscle were generally found in the groups exposed to 5 and 31 psu compared to the 15 psu group. Only the pepsin activity (digestive enzymes) assessed enhanced with environmental salinity, while pyloric caeca trypsin/chymotrypsin ratio decreased. This study suggests that juvenile of E. maclovinus presents greater growth near its iso-osmotic point (15 psu) and hyperosmotic environment (31 psu). Acclimation to low salinity increased the osmoregulatory expenditure as seen by the gill and anterior intestine results, while at high salinity, branchial osmoregulatory activity was also enhanced. This requires the mobilization of lipid stores and amino acids, thereby holding the growth of fish back. The subsequent reallocation of energy sources was not sufficient to maintain the growth rate of fish exposed to 5 psu. Thus, E. maclovinus juveniles present better growth efficiencies in salinities above the iso-osmotic point and hyperosmotic environment of this species, showing their best performance at 15 psu as seen by the main osmoregulatory and energy metabolism enzymatic activities.

Effects of changes in salinity on oxygen and food consumption of the young sub-Antarctic notothenioid Eleginops maclovinus: possible implications of their use of an estuarine habitat

“…Meal size at 12 psu was 41.2 and 135.9 % greater than the meal sizes observed at 30 and 1 psu, respectively. This is in accordance with the findings ofVargas-Chacoff et al (2015) that acclimation of E.…”

“…-ATPase activity in posterior intestine. However, Vargas-Chacoff et al (2015) have described no differences in plasma cortisol level in individuals exposed to 5, 15 and 31 psu, and they interpreted this in the same way as for E. maclovinus which do not appear to exhibit chronic stress. Those authors hypothesize that there could be a discrepancy which can be explained by different times of acclimation.…”

“…Some parameters show a direct and positive relationship with salinity, while others show a U-shaped relationship. Moreover, Vargas-Chacoff et al (2015) demonstrated a better growth rate for E. maclovinus chronically exposed for salinities near to the iso-osmotic point (15 psu) than to the hyper-osmotic environment (31 psu). These changes are related to an allostatic energy response, and they likely impact on oxygen consumption.…”

Intermediary metabolic response and gene transcription modulation on the Sub‐Antarctic notothenioid Eleginops maclovinus (Valenciennes, 1930) injected with two strains of Piscirickettsia salmonis

“…Moreover, G6PDH activity in the liver of E. maclovinus varies depending on the stressor or condition utilized. For instance, in E. maclovinus acclimated to different environmental salinities, G6PDH in the liver did not show variation, whereas in individuals of the same species exposed to high salinity conditions, activity of G6PDH decreased (Vargas‐Chacoff, Moneva, et al, ; Vargas‐Chacoff et al, ). Additionally, an increase in the hepatic activity of G6PDH has been observed in E. maclovinus exposed to stressful high stocking density conditions (Vargas‐Chacoff, Ortiz, et al, ).…”

Can intraspecific variations be exploited to develop salinity tolerance of Oreochromis niloticus?

“…Altinok and Gizzle (2001) reported that the needs of nutrients and protein may differ between freshwater and salt water species to influence metabolism and homeostatic processes in fish. Also, high metabolic rates can be explained by action of salinity upon digestive enzymes, where the exposure to different salinities change the ionic concentration in the gastric lumen, consequently may alter digestive enzymes activities which affect feed digestibility and fish growth performance (Vargas-Chacoff et al, 2015).…”