ENGLISH ABSTRACT: Currently, South African aquaculture is dominated by the cultivation of Haliotis midae, which is estimated as the most lucrative sector of the industry, with 934 t being export in 2008, totalling an income of ZAR 268 million (40 million USD) in 2008. This represents 81% of the total rand value of the aquaculture sector. Abalone was the highest aquaculture commodity exported during the last two years from South Africa, representing 24% of the total tonnage exported. Employment in the aquaculture sector increased by approximately 80% between 2005 and 2008, and was highest in the abalone sector where the number of people employed increased by 234%.
Despite these high production rates, no hatchery procedures have been developed specifically for H. midae. Most procedures and protocols currently used in South African abalone hatcheries have been adopted from cultivation methods used for foreign species. Although certain aspects of reproduction are universally conserved between abalones, it is important to consider the physiology and the origin of the species studied.
To date, no scientific research has been conducted on the reproduction of H. midae, except for a few studies in the early 1990s, which focused on the basic reproduction of this species. No further studies have been done on H. midae reproduction under intensive culture. Currently, hatch-out rates obtained by most abalone farms in South Africa averages 80%, with a 50% settlement rate, and a final hatchery output of only 30%.
This study reports on various aspects of H. midae reproduction that can influence its commercial culture. A detailed histological characterisation of gametogenesis was developed. Findings indicated that cultured H. midae reaches 50% sexual maturity at a shell width of between 25 mm and 30 mm.
During fertilisation trials, a sperm concentration of 50 000 sperm mL-1 and egg concentrations lower than 50 eggs mL-1 produced the highest hatch-out rates. Whilst fertilisation volume did not influence fertilisation success, fertilisation potential of the eggs did decrease with time. Eggs older than 100 minutes showed a lower fertilisation potential than eggs fertilised earlier.
A larval stress test was developed to evaluate larval resistance against chemical stress. It was determined that 50% of resultant larvae would exhibit morphological abnormalities after fertilised eggs were incubated in 0.7% dimethyl sulfoxide (Me2SO) for a 24 hour period. If larvae exhibited fewer abnormalities at this concentration, it could be deduced that the larvae had a high resistance to the negative effect of the toxicant, and could thus be seen as good quality larvae.
When evaluating hybridisation potential between H. midae and H. spadicea, it was found that it was possible to fertilise spawned H. midae eggs with biopsied H. spadicea sperm.
By incorporating the results obtained from the present study into current hatchery systems on South African abalone farms, higher hatchery yield could be achieved, which in turn would lead to an increase in commercial revenue. AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse akwakultuur sektor word tans oorheers deur die produksie van Haliotis midae, en word gereken as die mees winsgewendste bedryf in die industrie, met 934 t uitgevoer in 2008, na-raming „n inkomste van ZAR 268 miljoen (40 miljoen Amerikaanse doller). Dit verteenwoordig sowat 81% van die totale rand waarde in die akwakultuur bedryf. Perlemoen was ook die grootste uitvoer kommoditeit gedurende die laaste twee jaar, en het tot sowat 24% van die totale uitvoer vanuit akwakultuur bygedra. Werksgeleenthede in die akwakultuur sektor het tussen 2005 en 2008 met ongeveer 80% gegroei, waarvan die hoogste groeisyfer in die perlemoen bedryf was, waar die aantal werknemers met 234% toegeneem het.
Ten spyte van hierdie hoë produksie omset, is daar tans geen protokolle wat spesifiek vir die produksie van H. midae ontwerp is nie. Meeste van die tegnieke wat huidiglik gebruik word op Suid-Afrikaanse plase, is gebaseer op, en aangepas vanaf metodes daargestel in die internasionale bedryf vir uitheemse spesies. Alhoewel sekere aspekte van reproduksie tussen perlemoen spesies verband hou, is dit belangrik om die fisiologie en oorsprong van die spesie van belang, in ag te neem. Wetenskaplike navorsing gedoen op die reproduksie van H. midae is beperk tot studies in die vroeë 1990s, wat die basiese beginsels van die spesie se reproduksie ondersoek het. Daar is geen verdere studies op die reproduksie van H. midae, veral onder intensiewe teel toestande, gedoen nie. Tans toon die meeste perlemoen plase in Suid-Afrika „n produksie persentasie van ongeveer 80% larwes vanaf bevrugting, met „n afname na 50% met vestiging en „n gevolglike uitset van slegs 30%.
Hierdie studie doen verslag oor verskeie reproduksie aspekte van H. midae wat die teel doeltreffendheid van perlemoen op kommersiële plase kan beïnvloed. „n Gedetaileerde histologiese karakterisering van gametogenese is ontwikkel. Daar is gevind dat geteelde perlemoen 50% geslagsrypheid bereik met „n skulp wydte van tussen 25 mm en 30 mm.
Tydens bevrugting eksperimente is bepaal dat 50 000 sperm mL-1 en „n eier konsentrasie van laer as 50 eiers mL-1, die optimale gameet konsentrasies is vir effektiewe bevrugting. Alhoewel die volume water waarin bevrugting plaasvind nie „n invloed getoon het op bevrugtingsukses nie, is daar wel gevind dat die eiers se potensiaal om bevrug te word, afneem met verloop van tyd. Eiers ouer as 100 minute het „n verlaagde bevrugtingspotentiaal getoon teenoor eiers wat vroeër bevrug is.
„n Larwale stres toets is ontwikkel om larwale weerstand teen chemiese stres te bepaal. Daar is gevind dat 50% van geproduseerde larwes morfologiese abnormaliteite sal toon indien bevrugte eiers vir „n periode van 24 uur in 0.7% dimetiel sulfoksied (Me2SO) geïnkubeer word. Indien larwes minder abnormaliteite toon by hierdie konsentrasie, beteken dit dat hierdie larwes meer weerstand kan bied teen die negatiewe effek van die toksiese middel, en dus beskou kan word as goeie kwaliteit larwes met hoë lewensvatbaarheid.
Met die evaluering van hibridisasie potensiaal tussen H. midae en H. spadicea, is gevind dat dit moontlik is om vrygestelde H. midae eiers te bevrug met H. spadicea sperm wat verkry is deur „n biopsie.
Die implementering van hierdie studie se bevindinge in kommersiële H. midae produksiesisteme sal daadwerklik bydra tot die optimisering van bestuurspraktyke en „n verhoging in die totale produksie doeltreffendheid van sulke sisteme. Description:
Thesis (PhD (Genetics))--Stellenbosch University, 2011.
Doctoral Degrees (Genetics)