Ventilation Rate and Behavioral Responses of Juvenile Mahimahi to Temperature and Salinity

Abstract

Abstract In an effort to document symptoms of shortterm stress in culture tanks, juvenile mahimahi (or dolphins, Coryphaena hippurus) were held in 500–700 L seawater at densities of about 0.1 fish/L and subjected to continuous changes in temperature and salinity over several hours. Ventilation rate, indexed by rate of opercular beat, and behavior patterns including body orientation and position within tanks were recorded. Ventilation rate was relatively sensitive to temperature change, and increased linearly with rising temperature until stress symptoms, including mortality, began near 30°C. Decreasing temperature to 16°C reduced ventilation rate; there was no mortality, but the fish ceased feeding. Decreasing salinity from 35‰ to 0‰ produced no significant change in ventilation rate, no mortality, and no qualitative effect on feeding vigor (at 9.5‰, the only value tested). All fish tested survived 1 h at 0‰. Behavior at high temperature resembled that reported for freshwater fishes under severe high-temp...