Growth, food intake regulation and metabolic adaptations in goldfish (Carassius auratus) exposed to different salinities

The aim of the present study was to investigate the effects of different salinities (0, 2, 4, 6, 8 and 10 parts per thousand) on food consumption, growth, metabolic resources, and several stress indicators in goldfish. Possible changes in feeding regulators, brain neuropeptide Y, circulating ghreline, and the hypothalamic morroaminergic transmission were also examined. Salinities up to and including 6 parts per thousand did not affect weight gain, standard growth and feed conversion rates. The goldfish showed good adaptation to these salinities in terms of metabolic resources (lipids and glycogen content in liver and muscle) after 21 days of salinity exposure. The unaltered haematocrit, haemoglobin, glycemia and plasma cortisol levels indicated that salinities up to and including 6 parts per thousand do not produce significant stress in goldfish. Higher salinities (8 and 10 parts per thousand) produced significant muscle dehydration, significant increases in circulating cortisol, and adverse effects on growth, food intake and food conversion rate. Although this salt-induced reduction in food intake does not appear to involve either central (neuropeptide Y) or peripheral (ghrelin) potent orexigenic regulators for this species, a possible role for the hypothalamic serotoninergic system cannot be discarded. Diurnal locomotor activity was significantly lower in all goldfish exposed to salinity compared to FW fish. In conclusion, Carassius auratus, a freshwater stenohaline fish exhibits good growth and no signs of stress in saline waters up to 6 parts per thousand salinity. These results demonstrate that using such salinities to reduce the incidence of diseases and mortality does not produce significant physiological alterations in this species. (c) 2008 Elsevier B.V. All rights reserved.