Abstract
Survival and physiological parameters associated with metabolism and osmoregulation were evaluated in juveniles of the Lebranche mullet Mugil liza acclimated to different water salinities (5, 10, 20, 30, and 40‰) for 15 days. Room temperature (25ºC) and photoperiod (12L:12D) were fixed. Fish were fed twice-a-day with commercial diet (28% crude protein) until satiation. After acclimation, whole body oxygen consumption was measured and fish were euthanized and sampled for blood, gills, and liver. Whole body oxygen consumption and plasma osmolality did not change in the range of salinities tested. The isosmotic point was estimated as 412.7 mOsmol kg-1 (13.5‰). Gill Na+,K+-ATPase activity tended to be lower at 20 and 30‰, while liver glycogen content was significantly higher at 20‰ than at 5 and 40‰. These results indicate that juvenile M. liza is able to acclimate for a short-period of time (15 days) to a wide range of salinities (5-40‰). This condition is achieved through adjustments in gill Na+,K+-ATPase activity and carbohydrate metabolism to regulate plasma osmolality and aerobic/energy metabolism. Therefore, our findings support the idea of catching juveniles M. liza in sea water and rear them in estuarine and marine waters.
Highlights
Aquaculture practices seek to develop a healthy and sustainable environment through the control of biotic and abiotic factors in order to maximize fish growth
Juveniles of the Lebranche mullet Mugil liza are naturally subjected to important changes in environmental salinity over its life cycle
An adequate ability to cope with these changes is imperative for M. liza to complete its life cycle. This ability was clearly observed in juvenile M. liza exposed to a wide range of salinities. This statement is based on the following facts: (1) juvenile mullets tested in the present study were able to survive after abrupt transfer from sea water (30‰) to a wide range of experimental salinities (5-40‰); (2) no significant change in plasma osmolality was observed after acclimation of juvenile mullets to the different environmental salinities, and (3) the slope of the regression line between plasma and water osmolality was not significant (b = 0.023), indicating a strong capacity of juvenile mullets to regulate plasma osmolality in a wide range of water salinities
Summary
Aquaculture practices seek to develop a healthy and sustainable environment through the control of biotic and abiotic factors in order to maximize fish growth. The influence of water salinity on fish growth has been reported for several species (Woo & Kelly, 1995; Sampaio & Bianchini, 2002; Resley et al, 2006), including the mullet Mugil liza Valenciennes, 1836 (Lisboa et al, 2015). I.e. below the isosmotic point, they absorb salts (Na+ and Cl-) through the gills to counteract the diffusive loss of ions. I.e. above the isosmotic point, they drink and desalinize sea water at the digestive tract. In this case, water is osmotically absorbed through the intestinal wall and the excess of salts
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