Date of Award

12-2003

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Ione Hunt von Heribing

Second Committee Member

Linda Kling

Third Committee Member

Bruce Sidell

Abstract

The larval stage of marine fish is a period of rapid growth and development. Atlantic cod (Gadus morhua) are approximately 4-5 rnm in length upon hatch and feed endogenously from their yolk sac for the first week. After this time, larval cod must successfully capture live prey to survive and to fuel high growth rates of greater than 10%d". Previous studies have found that during exogenous feeding and at growth rates greater than 8%d1 larvae experience what appears to be cost free growth, where mass specific metabolic rate does not decrease with increasing mass. Due to size and condition constraints involved in working with larval marine fish, few data exist on the metabolism of early larval growth. This study was done using microcalorimetry to identify specific dynamic action (SDA) which represents the cost of feeding, digestion, and protein assimilation (growth) in larval cod. Cod were used in the experiments only after the yolk sac was completely utilized, and the larvae were feeding exogenously. This study was the first to record changes in metabolic rates as a function of feeding in larval fish using a microcalorimeter. Growth rates for two populations (Rhode Island and Newfoundland) of Atlantic cod were measured and ranged from 6.9%d-' to 13. l%dml, showing that larvae grew well under culture conditions. After comparing mean growth rates between the two populations and finding them to be significantly different, only Newfoundland cod were used in the experiments to measure SDA. Using a ThermometricO LKB 2277 microcalorimeter (TAM) the total heat output of larval cod fiom 10 - 40 days post hatch was determined under two different feeding conditions. Two cod of the same age (days post hatch) were placed concurrently into the microcalorimeter in one of two channels. One cod larva was left unfed for at least 12 hours prior to the experiment (unfed) while the other was fed to satiation immediately before the experiment was run (fed). TAM measurements showed that for the first 30 days post hatch (dph), both fed and unfed larval cod showed increases in mean heat output on a daily basis. During this time fed larvae had a significantly higher average heat output than unfed larvae. From day 30 through 40 post hatch, fed larvae were observed to have a lower mean daily heat output when compared to unfed larvae. This change in mean daily heat output may be attributed to factors involved in the transformation stage of the larvae to the juvenile stage such as more efficient digestion and increased swimming and searching activity.

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