Energy Budget of Early Juvenile Cobia, Rachycentron canadum

Cobia, Rachycentron canadum , aquaculture is a rapidly developing field with considerable information known about juvenile production, but rearing conditions and protocols for hatchery production are not fully optimized. Setting up an energy budget for young cobia would facilitate the identification and optimization of factors controlling their rapid growth. This study measured several of the components of the energy budget of six different size classes (25–50 mm total length; 8.67–75.45 mg dry weight) of recently weaned cobia including growth rate, daily feed consumption, and metabolic rate. As expected, their specific growth rates were high ranging from 36.8% body dry weight/day in the smallest fish to 17.6% in the largest size class. Cobia grew an average of 2.6 mm/d or 6.9 mg dry weight/day. Daily ration levels were high, decreasing from 19 to 14% of body wet weight/day as the cobia grew. The high growth rates and food intake were concomitant with high feed conversion efficiencies that ranged from 1.66 in the smallest fish to 1.18 in the largest size class. Oxygen consumed by individual fish increased significantly with size from 0.10 to 0.54 mg/h with a scaling exponent for standard metabolic rate to dry weight of 0.805. The proportion of consumed energy used for metabolism remained fairly constant at 42–49% throughout the size ranges evaluated, while the cost of growth decreased with increasing size from 27% of consumed calories to 19%. Waste (fecal + urinary) calories, estimated by balancing the energy budget, averaged 34% of consumed calories. From this work, it is apparent that the rapid growth rates exhibited by cobia during the early juvenile phase result from high‐energy intake (consumption) and high feed efficiencies and not from any metabolic efficiency.