Abstract
The abalone, Haliotis iris and H australis, are candidates for aquaculture in New Zealand. There are some fundamental difficulties facing aquaculturists attempting to farm these species. New Zealand abalone farmers often have difficulty in sourcing abalone from the wild that are ripe enough to be spawned. There is also a lack of information on protocols for conditioning wild broodstock for successful spawning induction. In addition, there are difficulties with induction of spawning of ripe abalone to yield high quality eggs. These problems stimulated the undertaking of this study with the broad aim of developing a better understanding of the environmental, chemical and hormonal aspects of reproduction of these two species.
The reproductive cycles of Haliotis iris in southern New Zealand (Picton, Warrington and Stewart Island) and H australis (Warrington) were examined histologically over a 24-month period. Gonad index, oocyte size frequency and standardised residual analysis were applied to document gametogenic cycles and spawning events. The H iris population at Picton displayed an annual reproductive cycle, with gonad development and spawning between sexes occurring asynchronously (ANOVA, P=0.006). Spawning in this population occurred during winter and early spring in both 1997 and 1998. A pre-spawning peak in gonad increment was observed in summer and autumn months. The gonad indices of males were higher in January to April 1997 than for the females but the reverse occurred in the same months in 1998. These findings demonstrate how temporally variable the reproductive cycle can be between years in a population. The reproductive cycle of the Stewart Island population was not annual but gonad development and spawning between sexes was synchronous (ANOV A, P=0.96). A large spawning occurred in late winter and early spring in 1998 and a partial spawning in autumn 1998. No spawning occurred in 1997 although the goand index remained consistently high (between 71-85%). Warrington population showed consistently low gonad indices with very small seasonal fluctuations. There was some evidence of spawnings in summer and autumn in 1996-97. The mean gonad index remained between 35-60% until the end of 1997 but afterwards climbed close to 70% but no spawning was observed in 1998. The reproductive cycle of the H australis population in Warrington was annual and synchronous among sexes (ANOVA, P=0.48). Spawning occurred in summer and autumn in both 1997 and 1998. Another major spawning was recorded in the spring of 1996, but this was not repeated in 1997.
There was no relationship between photoperiod and changes in gonad development in H iris (Picton, r2=0.036, Warrington, r2=0.003 and Stewart Island, r2=0.0l 7) and H australis (r2=0.009). However, the H iris population at Picton showed a positive correlation between gonad development and sea surface temperature (P<0.05), but no such relationship was observed for the other sites. The changes in gonad indices in the Warrington and Stewart Island populations showed a strong relationship with the effective accumulative temperatures (EAT), which is the cumulative temperature above the Biological Zero Point (BZP) temperature.