Feeding dynamics of fish larvae on Copepoda in the western Irish Sea, with particular reference to cod Gadus morhua

Abstract

Cod and other species of fish larvae, and nauplii and copepodite copepods, were sampled in the western Irish Sea in April/May 1988 and 1989. The diet of cod larvae was determined by gut analysis, and consisted almost entirely of copepods. The daily energy requirements of 3 sizes of cod larvae were determined from modified forms of published energetic models, and used to estimate numbers of copepods eaten per larva per day. The volume of water searched by larvae is modelled as a power function of larvae length. Modelling predictions indicate that cod larvae of < 5 mm length require high densities of copepod nauplii as they can search only small volumes of water. Larger larvae, 2 7.5 mm length, consume large numbers of copepodites and so require high densities of copepods to avoid depletion of the food resource. Observed copepod densities were sufficient for the energy requirements of the cod larvae populations at the densities observed in the western Irish Sea. However, when all species of larvae are considered, the model predicts that competition for food is likely to occur among larger larvae at observed copepod densities.

Wind mixing, food availability and mortality of anchovy larvae Engraulis encrasicolus in the northern Adriatic Sea

“…The values given by Hay et al (1988) and Thompson & Harrop (1991) were used for conversion of numerical abundance to dry weight.…”

Contrasting years of prey levels, feeding conditions and mortality of larval walleye pollock Theragra chalcogramma in the western Gulf of Alaska

“…Some studies report that prey concentrations may not be associated with survival, condition or abundance patterns of fish larvae (Rice et al 1987, Taggart & Leggett 1987, Owen et al 1989, Thompson & Harrop 1991, Bollens et al 1992, McGurk et al 1993. Other studies report that average prey concentrations may limit larval growth (Shelbourne 1957, Cohen & Lough 1983, Gadomski & Boehlert 1984, Fortier & Gagne 1990, Fossum & Moksness 1993.…”

Diet affects the redox system in developing Atlantic cod (Gadus morhua) larvae

“…Copepods are the natural diet of cod larvae [33], and result in superior larval growth and development compared to when rotifers are fed [1,3]. Thus, in the current study we hypothesise that the redox regulation in copepod-fed larvae during development is an optimal state, and that differential regulation from this optimum induced by the rotifer diet represents dysregulation of this system.…”