Abstract
<p>Cobia (Rachycentron canadum) and mahi (Coryphaena hippurus) are top pelagic predators known for exhibiting rapid rates of development and growth throughout all life stages. Metabolic rates of embryonic stages of both species were studied to determine and compare the relationship between their metabolism and growth during early developmental stages. Metabolic rates (0.246 ± 0.035 μL 2/egg/hr) and weight-specific metabolic rates (2.562 ± 0.364 μL O2/mg dry weight/hr) of cobia embryos were not significantly different than metabolic rates (0.345 ± 0.05 μL O2/egg/hr) and weightspecific metabolic rates (2.199 ± 0.321 μL O2/mg dry weight/hr) of mahi embryos. Growth rates, length-weight relationship and condition factors were also determined and compared during the first 30 days post-hatching (DPH) of cobia and mahi larvae. Cobia larvae had an absolute growth rate (AGR) in length of 0.901 mm/day and wet weight of 4.2 mg/day. Length and weight specific growth rates (SGR) of cobia larvae were 7.37%/day and 21.7%/d, respectively. Mahi larvae had a length AGR of 0.965 mm/day, weight AGR of 10.57 mg/day, length SGR of 6.3%/day and weight SGR of 23.2%/day. No significant difference was found between cobia and mahi larval growth rates in length (ANCOVA; p<0.05). In weight, however, mahi larvae grew significantly faster than cobia larvae, F(1, 57) = 29.165, p < 0.001). Cobia and mahi larvae exhibit allometric growth rates, and their length (x) – weight (Y) relationships are best expressed by the following power equations: Cobia: Y = 0.01x2.7433 r2 = 0.9887 n = 792 Mahi: Y = 0.0024x3.4474 r2 = 0.9808 n = 720 Condition factor (K) for cobia larvae dropped from 1.03 to 0.37, while mahi larvae K value increased from 0.52 to 0.96 during the period studied (30 days post-hatch), when both species had reached juvenile stages. Metabolic rates and weight-specific metabolic rates of both cobia and mahi embryos were found to be higher than those reported for most other teleosts in the literature. Likewise, larvae of both species exhibit faster rates of development in length and weight than those reported for most other fish, and comparable to those of high performance pelagic species like tunas.</p>