Variance in rates of growth and development in larval and metamorphosing summer flounder, Paralichthys detatus

Summary Summer flounder, Paralichthys dentatus L., show variance in total length as they progress through larval development and metamorphosis, both in commercial aquaculture hatcheries and in research facilities. This variance leads to serious problems with cannibalism after settlement, if the fish are not graded(i.e. separated by size), a labor-intensive process. In order to document the magnitude of this variation and to try to understand the basis for it, we conducted a series of experiments during (a) the larval period and (b) the process of metamorphosis. The larval experiments were done on fish reared individually in small bowls and repeatedly measured during their development. The metamorphosis experiments were done on fish reared either communally or individually and repeatedly examined to determine the relationships between age, growth and stage of development. There was no relationship between size of larvae at 8 or 9 days after hatch (DAH) and their subsequent size at 30 DAH. During two larval trials, significant events occurred around 20-22 DAH: increased variability in size among offspring from one set of parents, and increased growth without increased variability among offspring from another set of parents. These findings suggest that selective breeding of this species might be a way of reducing size variability. During the metamorphosis trials, we found that rates of development and absolute growth in summer flounder are positively correlated.