Variation of Susceptibility to Thermal Shock in Developing Eggs of Dragonet, Repomucenus beniteguri

Abstract

Effect of a short-term thermal shock on developing fish egg was investigated using by dragonet, Repomucenus beniteguyi (Japanese name: Tobinumeri) . Seventeen different developmental stages of egg were exposed to six test temperatures (30.0-40.0°C, Δ_t = 7.5-15.5°C) for 15 min, and returned immediately to the initial spawning water temperature (22.5 ± 0.3°C) . From the results of hatching rate, median patchable shock temperature (MHST) was calculated for both total and viable batch at every tested stage.
Both MHSTs depended on the particular stage of development concerned at the time of shock. Lowest MHSTs were observed during the early cleavage stages, i. e., from one-cell to early morula stage. Consequently, these stages were presumed to be more susceptible to the thermal shock than any other stages. Thereafter the susceptibility decreased rapidly down to the blastula stage, then it increased a little at the blastopore closing stage. As the blastopre was closed, the egg again showed a decrease of the susceptibility until the stage soon before hatching.
Such variation of susceptibility in developing egg to thermal shock obtained from the present species is similar to those reported for Cyprinus carpio and Halichoeres poecilopterus.