Bioenergetics of juvenile cobia and billfish

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries

First Committee Member

Jerald S. Ault - Committee Chair

Second Committee Member

Daniel D. Benetti - Committee Member


The physiological energetics of juvenile cobia (Rachycentron canadum Linnaeus) and late larval stage billfish (Istiophoridae; Atlantic sailfish, Istiophorus platypterus (Shaw) and blue marlin, Makaira nigricans Lacepede) was investigated. Metabolism, excretion, growth and swimming performance of juvenile cobia and the energetic budget for young billfish were studied through direct and indirect methodologies to better understand the role of energy transformation in growth and survival. Mean oxygen consumption rates (VO2; mg O2 hr -1) of fed and starved cobia significantly increased with increasing weight (W; g-wet): VO2= 1.4291W0.8119 and VO 2 = 1.1784W0.7833, respectively. Urea excretion accounted for approximately half the total nitrogen excretion and mass specific urea rates were higher than those reported in the literature for all marine fishes. Sustained swimming speeds (U; cm sec-1) of juvenile cobia significantly increased with body length (SL): U = 4.45*SL + 1.94. Mass specific oxygen consumption (QO2; mg O2 g-1 hr -1) increased exponentially with swimming velocity (U; TL sec -1): QO2 = 0.3773*exp(0.2136*U). Comparison of metabolic rates and swimming performance to other species in the literature suggests that juvenile cobia rely on size rather than swimming ability to escape predation. It is hypothesized that cobia "rest" on the benthos to lower oxygen demand generated by their tissues. The function of billfish W and VO 2, which also reflects the cost of feeding (SDA), was VO2 = 0.0007*W1.1419 with a mean mass specific metabolic rate of 0.00268 mg O2 mg-wet-1 hr-1 (+/- 0.00275 sd). An analytical simulation model predicted billfish consumed 0.76 mg mg-1 d-1 which increased rapidly from 4.45 J d-1 at 3 days post hatch (dph) to 206.98 J d-1 by 15 dph at 29°C. This energy is partitioned into metabolism (23%), somatic growth (55%), non-fecal excretion (4% AMM and 3% Urea) and fecal excretion (15%). The relatively low contribution to metabolism may reflect an efficient coupling of metabolism and growth, rather than a low metabolic rate. The speculative energetic strategy of young billfish allows for precocious larval development which may benefit survivorship by providing early "size refuge".


Biology, Oceanography; Biology, Physiology

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