The Effects of Two Rearing Salinities on Survival and Stress of Winter Flounder Broodstock

Abstract

The goal of this study was to determine rearing conditions that would improve the survival of broodstock of winter flounder Pleuronectes americanus. We hypothesized that keeping wild winter flounder in iso-osmotic water would reduce the energy costs related to osmoregulation; the resulting energy gain could then be used for growth or immune responses. Eighty fish were randomly separated into four tanks, two containing seawater (SW; 28.7 ± 0.9‰ (mean ± SD)) and two containing brackish water (BW; 14.7 ± 1.7‰). Fish were sampled after 2 and 5 months of captivity for evaluation of their condition and stress status. Between the second and fifth months, the condition index increased significantly in both salinity groups, whereas body water content decreased. No salinity effect in terms of growth, condition, or energy reserves was found. However, the fish in BW showed much lower mortality. We found that the fish in SW had higher levels of the physiological indicators of stress than those in BW, which could have increased the risk of opportunistic infections in the former. Also, thrombocytes were absent in the SW fish after 2 months of captivity, which may have contributed to some mortalities. The lower resistance of certain opportunistic pathogens to BW is another possible explanation as to why fish in BW had lower occurrences of infectious diseases.

Alternative Methods for Measuring Energy Content in Winter Flounder

“…We only measured liver biochemical composition in the spring, just after the winter fast, when liver energy reserves were probably at their lowest. However, our study covered a wide range of HSIs slightly exceeding 3%, a range that has also been found throughout the year by other authors (Fletcher and King 1978;Barker et al 1994;Plante et al 2002). Since our study covered the whole range of HSIs found in winter flounder, biochemical compositions from other seasons would only increase data variance.…”

“…Winter flounder caught in 1997 were fed chopped fish (capelin Mallotus villosus or Atlantic herring). In 1998 the winter flounder were fed amphipods (Anonyx sarsi) and in 1999 the winter flounder were fed custom-made wet pellets (Plante et al 2002). All fish were fed a daily ration of 1.5% of their biomass.…”

Comparison of stress responses in wild and captive winter flounder (Pseudopleuronectes americanus Walbaum) broodstock

“…One challenge in the development of winter flounder broodstock is to keep healthy feral fish in captivity. Earlier studies have shown a high occurrence of opportunistic infections and high mortality when winter flounder are kept in captivity (Hoornbeek, Sawyer & Sawyer 1982; Burton & Idler 1987; Harmin & Crim 1992; Plante, Audet, Lambert & de la Noüe 2002). Common aquaculture husbandry practices, such as capture, handling, crowding, confinement, transport and anesthesia, often impose stress on captive fish (Barnett & Pankhurst 1998).…”

Salinity influences the humoral immune parameters of gilthead seabream (Sparus aurata L.)

“…In salmonids, for example, transference from freshwater to seawater (hyper-osmotic shock) decreased specificantibody production, but increased or had no effect on serum lysozyme and leucocyte phagocytosis and cell-mediated cytotoxicity [4,5]. Other studies have demonstrated that the grouper fry increases its susceptibility to IPNV [6], while cod and winter flounder increase their survival after pathogenic challenge when exposed to hypo-osmotic shock [22,23]. However, the data indicate that the resistance to pathogens is not due to an enhanced immune response but, more likely, to a lower degree of pathogenicity and a reduced occurrence of opportunistic parasites in the water.…”