Date of Award

5-2003

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

lone Hunt von Herbing

Second Committee Member

Linda J. Kling

Third Committee Member

Pete Jumars

Abstract

Growth rates of early life stages of Atlantic cod (Gadus morhua) are very high, but decline, as the fish grow larger. Little is know about the physiological processes that facilitate and regulate this growth pattern. In this study, feeding and swimming metabolism were measured in individual juvenile Atlantic cod (Gadus morhua) in order to investigate how energy are allocated to swimming and growth in fast growing stages of fishes. Metabolic rates were measured by the means of oxygen consumption using two "Brett-type" respirometers. The metabolic measurements were repeated several times in individual juvenile Atlantic cod with a wet body mass of 0.5-5.0 g over a period of 100 d. Wet body mass and total length of individual cod were measured biweekly during the experimental period and used together with metabolic measurements to determine the relationship between energy utilization and growth. The study consisted of two parts, 1) determination of aerobic scope for activity (the difference between standard and active metabolism), and 2) measurement of specific dynamic action (SDA, which represents the energy expenditure for ingesting, digesting, absorption of foodstuff, biochemical transformation of nutrients and assimilation of proteins). Power-performance relationships between oxygen consumption and swimming speed were established for juvenile Atlantic cod for the first time. Standard metabolic rate (RJ and active metabolic rate (R) were calculated fiom the power-performance relationships by extrapolating to zero swimming speed and maximum sustained swimming speed, respectively. Scope for activity was calculated as the difference between active and standard metabolism (&-F&). SDA duration, amplitude and magnitude were calculated by measuring oxygen consumption of fed and unfed fish swimming at a low cruising speed. Specific growth rates (G) ranged fiom 1.4 - 4.4% wet body mass dm' and decreased with increasing body mass. Scope for activity ranged fiom 10.2 to 40.7pmol 0 2 h-' for juvenile cod with a mass of 0.53-2.89 g. Scope for activity increased with increasing body mass, while mass-specific scope for activity (pmol02/M) decreased with increasing body mass. SDA peaked within 1 h after feeding for juvenile cod with a wet body mass of O.45-4.2Og, and peak values were 1.12-2.22 times the unfed values. SDA duration for juvenile Atlantic cod ranged fiom 2 to 8 hours. SDA magnitude ranged fiom 2.8 to 60.0 pmol 0 2 and increased with increasing wet body mass. Relative magnitude of SDA (percentage of the energy value of the ingested food) was found to be 0.18-3.84%. SDA amplitude accounted for 14.8-44.0% of the scope for activity. Results fiom this study suggest that the swimming and feeding metabolism in early stages of juvenile Atlantic cod differs fiom that of larger juvenile and adult cod. Major physiological differences include higher specific growth rates, shorter time to peak SDA, shorter SDA duration, lower relative SDA magnitude and a smaller portion of scope for activity taken up by SDA. Physiological differences among early juvenile and adult cod may be the result of the metabolic demand for high growth rates in small juvenile cod. Further research is needed to determine the physiological differences and the underlying mechanisms for different life stages of Atlantic cod and other temperate fishes.

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