Abstract
The purpose of this research was to spawn and settle larvae of the Yellowfoot Paua (Yellowfoot abalone) Haliotis australis (Gmelin, 1791) to investigate the early life stages of H. australis and the factors influencing settlement of the larvae of this abalone species in a commercial aquaculture context.
Scanning electron microscopy (SEM) was used to investigate the morphological aspects of the development of the life stages of Haliotis australis from gametes, veliger larvae, post larvae and juveniles to 60 days post settlement (70 days post fertilisation). The photo micrograph results presented in this thesis represent the first comprehensive SEM micrograph record of the early life stages of H. australis.
Settlement experiments tested success of larval settlement on four different diatom biofilm settlement substrates; 8-Day [old] Ungrazed Biofilm, 8-Day Grazed Biofilm (pre-grazed by conspecific adults to produce mucus trails), 1 Day Biofilm and No Biofilm. Half of the experimental replicates were settled with H. australis larvae treated with gamma(γ)-aminobutyric acid (GABA) to test the effectiveness of GABA as a chemical treatment to enhance settlement of H. australis larvae.
Post larval survival at 33 days post settlement was used to infer the settlement success occurring at the time of settlement (between Day-0 and Day-4 post settlement). Analysis of mean survival data at 33-days post settlement identified that established diatom biofilms pre-grazed with conspecific adults (8 Day Grazed Biofilms) produced higher settlement than one day old diatom biofilm (1 Day Biofilm) and No Biofilm (control) treatments. Established diatom biofilms (‘8 Day Ungrazed Biofilm’) produced higher settlement than ‘No Biofilm’ treatments. The differences observed were statistically significant.
The analysis of mean survival at 33-days post settlement identified that there was no significant difference detected between GABA and no-GABA treatments. However the observed results indicated that 8-Day Ungrazed Biofilms and 8-Day Grazed Biofilms treated with GABA, and untreated (no-GABA) 8 Day Grazed Biofilm settlement surfaces produced the best inferred settlement of H. australis larvae when compared to untreated 8 Day Ungrazed Biofilm and both GABA and no-GABA 1 Day Biofilm and No Biofilm treatments.
These results suggest that pre-grazing of prepared diatom film settlement substrates with conspecific adult or juvenile abalone may be employed by hatcheries to ensure the highest rates of settlement in H. australis larvae. When the pre-grazing of established diatom biofilms is not a practical option in a larger scale aquaculture context, then the treatment of competent H. australis larvae with a GABA solution prior to settlement may be used to enhance the success of settlements onto established diatom biofilms.