The Effect of Temperature Changes and Transport on Cutthroat Trout Eggs Soon after Fertilization

Abstract

This study was conducted to determine the effects of temperature changes during the first few hours after fertilization (AF) on egg survival of cutthroat trout Oncorhynchus clarkii and to determine the relationship between water hardening, egg transport, and temperature effects. Eggs from cutthroat trout of the Bear Lake-Bonneville strain O. clarkii utah were subjected to changes in temperature from the ambient hatchery water temperature (8.5°C) at either 5 or 60 min AF and were then transported for 6 h. There were seven test treatments: (1) 4.5°C at 5 min AF, (2) 4.5°C at 60 min AF, (3) 0.5°C at 5 min AF, (4) 0.5°C at 60 min AF, (5) 13°C at 60 min AF, (6) hatchery control (no transport, no temperature change), and (7) transport control (no temperature change). After transport, eggs were all returned to 8.5°C until the end of the study. Survival to eye-up ranged from 63.7% in the 13°C-60-min treatment to 80.1% in the 4.5°C-60-min treatment. Warm temperatures (13°C) resulted in significantly higher egg mortality than that of controls. There was no significant difference between transported controls and untransported eggs in eye-up, hatch, or deformity rates, indicating that transport, at least on paved roads, did not affect survival. Comparison of temperature shocks occurring immediately AF (5 min) and after water hardening (60 min) indicated that thermal shocks administered before water hardening were more detrimental than those occurring afterward. Declines in temperature to 4.5°C or 0.5°C did not significantly affect survival relative to at least one of the controls. The results indicated that (1) temperature increases were detrimental but decreases were not and (2) it is preferable to transport eggs after water hardening rather than before.