The effect of triploidy on the growth and survival of the indigenous abalone, Haliotis midae, over a 24 month period under commercial rearing conditions

Schoonbee, Lize (Stellenbosch : Stellenbosch University, 2008-03)

Thesis (MScAgric)--Stellenbosch University

Thesis

ENGLISH ABSTRACT: Triploidy is the genetic state of containing three sets of chromosomes per cell in stead of two as in diploid organisms. The South African abalone (Haliotis midae) is naturally a diploid organism that sexually matures between four to eight years of age. Early sexual maturity is a disadvantage in cultured abalone stock, as the process of gonad development and spawning is energy demanding, causing energy to be diverted away from somatic growth. This same problem has been extensively experienced in diploid bivalve molluscs, where triploidy has since been applied as a means to prevent sexual maturation from occurring, thereby speeding up the growth process and shortening the time to marketing. Because triploidy was effective in bivalves, it was thought that it could contribute to faster growth in abalone as well. A procedure for the induction of triploidy in the abalone, Haliotis midae, was developed by De Beer (2004) and yielded up to 100 percent triploidy in treated abalone larvae. The next step was to compare the growth of the diploids and triploids to establish whether there was indeed a growth advantage on the part of the triploids, in view of commercial application. By using the same techniques as described by De Beer (2004), three groups consisting of triploid and diploid siblings were produced and subscribed to a comparative growth trial. The groups were spawned in three different seasons. The main objective was to establish whether there was in fact a difference in growth between diploid and triploid siblings, and whether seasonal effects were associated with growth advantages for either triploids or diploids. The two growth parameters measured were shell length and body weight. Measurements commenced at eight months of age, when the abalone could be individually tagged and continued up to the age of 24 months. The over-all results provided no convincing evidence of statistically significant faster growth of triploid juveniles compared to that of diploids up to two years of age. Growth differences were detected between seasons, but could not confidently be ascribed to seasonal environmental effects. The regression of shell length to body weight was similar for diploids and triploids.

AFRIKAANSE OPSOMMING: Triploiede organismes bevat drie stelle chromosome per sel in plaas van twee soos dit normaalweg in diploiede diere voorkom. Die Suid Afrikaanse perlemoen (Haliotis midae) is van nature ‘n diploiede organisme wat tussen die ouderdom van vier tot agt jaar seksueel aktief word. Vroeë seksuele aktiwiteit is ongewens in kommersiële akwakultuur aangesien energie spandeer word aan gonade ontwikkeling in plaas van somatiese groei. Dieselfde probleem is vroeër in die oester bedryf ondervind waar dit deur middel van triploiede induksie aangespreek is. Triploiedie veroorsaak steriliteit en kan gebruik word as ’n metode om steriliteit op groot skaal te induseer. Steriliteit sou dan meebring dat meer energie beskikbaar is vir somatiese ontwikkeling, wat verhoogde groeitempo en n verkorte tyd tot bemarking beteken. Op soortgelyke wyse is dus gepostuleer dat triploiedie in perlemoen ook tot steriliteit kon lei. ‘n Triploiede induksie metode was ontwikkel deur Mathilde de Beer (2004) wat ‘n hoë persentasie triploidie in geinduseerde perlemoen opgelewer het. Die volgende logiese stap was om die groei van diploiede diere met die van triploiede diere te vergelyk om te bepaal of triploiedie wel ’n groei voordeel tot gevolg het met die oog op kommersiële toepassing. Deur van dieselfde tegnieke as De Beer (2004) gebruik te maak, is drie groepe, elk bestaande uit verwante diploiede en triploiede diere, geproduseer en ingeskryf aan n vergelykende groei proef. Die groepe was in drie verskillende seisoene geproduseer. Die hoof doelstelling van die proef was om groeitempo van diploiede en triploiede diere te vergelyk, asook om die invloed van seisoen op groei van diploide en triploide te bepaal. Twee groei eienskappe naamlik skulp lengte en liggaamsmassa is gemeet vanaf ‘n ouderdom van agt maande (wanneer die diere individueel gemerk kon word) tot ‘n ouderdom van 24 maande. Die algehele resultate het gedui op geen betekenisvolle verskil tussen die groei van triploiede en diploiede perlemoen tot op die ouderdom van twee jaar. Verskille het voorgekom in die groei tussen seisoene, maar daar kon nie bewys word dat die verskille die gevolg van seisoenale omgewingseffekte was nie. Diploiede en triploiede het dieselfde skulp lengte tot liggaamsmassa verhouding getoon tot op twee jaar ouderdom.

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