Temperature induced changes in the development of embryos and paralarvae of the merobenthic octopus, Octopus tetricus

Abstract

Incubation temperatures can extend or decrease the time required for the embryos of marine invertebrates to hatch, while also greatly influencing the morphology and survival of hatchlings, characteristics which are of critical importance in hatchery production. This study examines the effect of incubation temperatures (16, 19, 22, 25 °C and ambient seawater temperature) on the development time to hatch, egg morphometric ontogeny and the hatching success in the common Sydney octopus, Octopus tetricus. These parameters were assessed at regular intervals for eggs from three broods placed in artificial incubation tanks at four temperatures between 16 and 25 °C, while the remainder of the eggs for each of the broods were incubated in ambient seawater under female care. The time to hatch had an inverse relationship to incubation temperature with the egg development time to hatch being halved at 25 °C (26–32 days) compared to 16 °C (67–69 days). Despite the markedly different development times there were no differences in the survival or quality of the resulting hatched paralarvae, although there was an overall tendency for inner yolk sac volume to decrease with increasing rearing temperature but not consistently among broods. There were differences in the number, size and quality of embryos in the three broods which tended to persist throughout their development, but these did not appear to be related to the size of the female octopus or water temperature prior to egg laying. The overall hatching success of eggs in artificial incubation tanks was above 90% for the brood of one female (F1) while for the other two it was 71% (F3) and 57% (F2) mostly likely as a direct result of being compromised by infection of the egg strings. Improvements in hatchery practice is required to prevent such infections for future paralarval production. The results demonstrate a wide thermal tolerance for the early developmental stages of O. tetricus with the potential to manipulate egg incubation temperatures to better meet the timing of hatchery production requirements.