No abstract

The osmoregulatory responses of 20 days of acclimation to environmental salinities of 5‰, 15‰, 25‰, 35‰ and 55‰ were assessed in juveniles of wedge sole (Dicologoglossa cuneata Moreau, 1881). This sole shows a good capacity to adapt to this range of environmental salinities. A direct linear relationship between environmental salinity and plasma osmolality was observed, with a calculated isosmotic point of 10.4‰ (284 mOsm kg−1). Na+, K+‐ATPase activity in the gills followed a ‘U‐shaped’ relationship with environmental salinity, and a direct linear relationship in kidney tissue. Plasma cortisol levels were elevated in fish held in extreme salinities, and glucose levels were higher only in the group maintained at the highest environmental salinity. In the liver, a decrease in glycogen, lactate and amino acid contents was observed in specimens acclimated to extreme salinities (5‰ and 55‰), suggesting mobilization of liver metabolites. Metabolite levels in white muscle showed a pattern similar to the liver, with lower values in specimens acclimated to extreme salinities. We conclude that wedge sole is strongly euryhaline, but acclimation to extreme salinities comes with an energetic cost.

Effects of two binders (gelatine and alginate) were tested on growth, survival, partial energy balance and lipid composition of mantle and digestive gland (DG) of Octopus vulgaris. The three diets tested were given as follows: CON, (Loligo gahi) as control, GEL, composed of squid paste (L. gahi) (300 g kg−1), fish hydrolyse CPSP® (100 g kg−1) and fish meal (500 g kg−1), agglutinated with 100 g kg−1 of gelatine and ALG, composed of squid paste (L. gahi) (300 g kg−1), fish hydrolyse CPSP® (100 g kg−1) and fish meal (500 g kg−1), all agglutinated with 100 g kg−1 of alginate. Growth rates were 13.7 ± 2.1, 2.1 ± 2.8 and −2.4 ± 2.9 g kg−1 bw day−1, for octopuses fed CON, GEL and ALG diets, respectively. DGs of octopuses had higher concentrations of fatty acids (FA) than the mantle. DG of animals fed CON had higher concentrations of FAs than those fed the artificial diets. Energetic balance demonstrated that physiologically useful energy for maintenance E(B) was affected by type of diet, with negative values of E(B) in animals fed ALG and positive (85 and 154 kJ kg−1 day−1) in octopuses fed GEL and CON, respectively. The ALG diet did not cope with the physiological requirements for octopus growth.