Abstract

Mullet (Mugilidae) are distributed worldwide in temperate and tropical marine environments, are eurytolerant of variable conditions, are commercially exploited, and have been used as a model for marine stock enhancement. Given this eurytolerance and the apparent decline of mullet in the northern Gulf of Mexico, we were interested in quantifying the influence of temperature and salinity on growth as it relates to the determination of optimal field growth conditions. We grew young juvenile mullet in a randomized and interspersed 3x4 factorial design (20, 25 and 30°C and 3, lO, 17 and 24°/00) with nine replicates each (five fish/replicate) over a 30 day periodo Results from the laboratory experiments revealed significant temperature (p < 0.001) and salinity (p = 0.019) effects on growth, with no interaction term (p = 0.964). These data suggest optimal growth occurred at temperatures ~ 25° C, and, within each temperature treatment, peak growth occurred at 17°/00' To compare these results to growth in the field, modal shifts in length-distributions of recruiting cohorts of young juvenile mullet were considered in relation to continuous changes in ambient abiotic conditions monitored with Hydrolabs at two widely-separated locations (45 km apart) along the Mississippi coast. Modal standard length change of young juvenile mullet over a seven day period was 3.4 mm (0.486 mm/d) at the Marsh Point location and was 2.2 mm (0.314 mm/d) at the Henderson Point location over the same time periodo This is a 35.4% difference in standard length over seven days, which when coupled with the salinity and temperature data noted above, parallel and generally support the differences observed from the laboratory growth experiments.

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