Culture of summer flounder Paralichthys dentatus: Environmental and endocrine synchronization of growth and settlement in larvae and identification of stressors in juveniles

Steven Gavlik, University of Rhode Island

Abstract

This dissertation addresses the variability in settlement behavior, growth and development during metamorphosis of summer flounder. There were three objectives: (1) Expand basic knowledge of hormonal and environmental factors that regulate timing of metamorphosis, (2) develop hormonal and environmental techniques that promote synchronization of metamorphic growth and settling behavior in order to eventually reduce cannibalism in juveniles, and (3) identify stressful culture practices and evaluate their long-term effects on growth in juvenile flounder. ^ The first and second objectives were accomplished through manipulations of cortisol and thyroxine and of rearing salinity. Endogenous whole-body cortisol concentrations increased through the late larval stages, peaked (∼12 ng/g) during prometamorphosis, and then declined during metamorphic climax. Immersion of 55 day-old flounder in 1.45 ppm (4 μM) cortisol in seawater elevated tissue levels to 12.3 ± 4.2 ng/g. One- or two-week immersion of metamorphosing flounder in 4 μM cortisol decreased growth and survival and did not synchronize growth. Immersion in thiourea to reduce thyroxine synthesis in late larval stages, followed by thyroxine during climax, was effective in synchronizing flounder settling behavior, growth, and development. Lowering salinity from 30 to 20 ppt beginning in late larval development increased growth and settling behavior of metamorphosing summer flounder. The thyroid hormone and salinity manipulations may be useful in reducing cannibalism and the labor associated with size grading. ^ The third objective considered crowding and handling as stressors in juvenile flounder. Resting cortisol levels were low (∼1–3 ng/ml), but comparable to other sedentary species. Crowding significantly elevated cortisol (4–22 ng/ml) within 1–4 hours. Recovery to resting levels by 24 hours occurred on 1 of 3 occasions. Daily exposure to crowding and/or handling for 5–6 weeks did not reduce growth, confirming the suitability of juvenile summer flounder for intensive, land-based aquaculture. ^ In summary, this dissertation describes aspects of the early development of cultured summer flounder and uses this information, and aspects of their natural history, to solve problems encountered in aquaculture. ^

Subject Area

Biology, Oceanography|Biology, Animal Physiology|Agriculture, Fisheries and Aquaculture

Recommended Citation

Steven Gavlik, "Culture of summer flounder Paralichthys dentatus: Environmental and endocrine synchronization of growth and settlement in larvae and identification of stressors in juveniles" (2004). Dissertations and Master's Theses (Campus Access). Paper AAI3145416.
http://digitalcommons.uri.edu/dissertations/AAI3145416

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