Student Research Project
Environmental and Physiological Regulation of Metamorphosis in Summer Flounder (Paralichthys dentatus)

Students
Meg McArdle
Major: Zoology
Future Plans: Career in marine biology

Lisa Menard
Major: Zoology
Future Plans: Family medicine

Michele Ledoux
Major: Zoology
Future Plans: Emergency medicine or pediatrics

Robin Katersky
Major: Zoology
Future Plans: Career in aquaculture

Professor
Jennifer Specker, Professor, Research Associate Professor David A. Bengtson, Department of Biological Sciences, University of Rhode Island, Kingston

We are discovering how external and internal factors affect early development in the summer flounder. This flatfish, like other vertebrates, begins life with a symmetrical body plan. In its larval stage, the flounder swims about the sea much like other fishes. During a process called metamorphosis, the flounder changes its body form and begins to dwell on the sea floor. A remarkable part of metamorphosis is the migration of one of the eyes so that both eyes are on the same side of the body. Pigmentation also becomes asymmetrical, typically with the down side remaining unpigmented while the top side becomes camouflaged.

This is a dramatic example of an irreversible change in body form to occupy a new habitat. Another example of metamorphosis among vertebrates is the tadpole-to-frog change in body plan. The evolutionary forces that select this complex life cycle are widely debated. To settle this debate, we need more understanding of the proximate factors regulating metamorphosis. An additional reason for understanding factors regulating metamorphosis in flatfishes is arising due to our growing need to culture edible fishes in captivity.

In our laboratory, we raise larval-stage flounder for up to three months. The undergraduates conducting these studies examine the fish under a dissecting microscope every few days. The total length of each animal is recorded and, based on fin ray resorption and eye position, the fish is assigned to a stage of development. In this way we can understand the relationship between rate of growth and rate of development. External variables such as salinity and temperature are varied and their effects on rates of growth and development can be analyzed. Chemical signals, such as thyroid hormones of the endocrine system, are varied, and the effects on rates of growth and development are analyzed.

We found that the rates of growth and development are positively correlated. Faster-growing fish also enter metamorphosis at a younger age. We also found that by inhibiting the thyroid hormones, we can delay metamorphosis.

Our results show that for summer flounder to metamorphose at an early age, say one month instead of three months, they require a rapid growth rate. We also know that metamorphosis is regulated in part by thyroid hormones.

As we collect data in the laboratory, we conduct the intellectual exercise of seeing how these data compare to what is known about summer flounder in nature. Does it make sense that salinity affects the length of the larval period? Does it make sense that thyroid hormones regulate growth and development?

In the future, we hope to contribute our information on proximate factors affecting metamorphosis to the debate about the ultimate factors that selected for this complex life cycle. We may also be able to assist in the effort to culture these fish for food production.

Return to Main Page

Copyright © The McGraw-Hill Companies, inc. Permission required for reproduction or display.