The evaluation of biological, mechanical and chemical methods to contain South African abalone species (Haliotis midae)

[摘要] ENGLISH ABSTRACT: Haliotis midae (HM) is one of five indigenous abalone species occurring along the coast of South Africa, andis the only species commercially cultivated in open flow-through systems. Commercial production of HMcontributes the most to income generated from aquaculture species in South Africa. Exports in 2011 totalled1036 ton, which amounts to an income of ZAR 369 million (40 million USD). Commercial production of HM ischaracterized by a long interval (i.e. up to five years) to harvest. Genetic modification of HM to improvegrowth rate in HM can potentially decrease the interval from hatch to harvest, which will contribute tooptimising the cost-efficient production of HM. However, a major concern in the production of geneticallymodified (GM) abalone is their escape from production systems, and the potential impact of the GM animalson the natural stocks in the surrounding environment. The implementation of containment methods toprevent the escape from GM abalone from production systems will assist in the management of the potentialecological risks escaped GM abalone may pose. Currently no containment strategies exist for the SouthAfrican abalone industry, which limits the use of transgenic biotechnologies to optimise the cost-efficientproduction of HM. The study therefore investigated the potential of biological methods (triploid induction),mechanical methods (polypropylene filter bags and obstructive materials), and chemical methods (sodiumhypochlorite and chlorine dioxide) to contain transgenic HM in open flow-through systems.Histological evaluation of gonad tissue samples of 16 triploid male and 15 triploid female HM indicated thattriploid induction was unsuccessful in arresting gonad differentiation, development, and function. Acombination of immature and mature gametes was observed on both triploid male and female gonads. Thefertilizing potential of biopsied sperm obtained from triploid and induced diploid male HM was assessed infertilization trials using ova obtained from diploid HM. No larvae were observed from the fertilizationtreatments of triploid male biopsied sperm, however, abnormal larvae (0.01% fertilization) were observedwhen induced diploid sperm were used to fertilize diploid ova.Polypropylene filter bags (100 μm) were not effective in containing male and female gametes in thebroodstock section of the abalone culture system used in this study, and future studies should addressspecialized methods of containment of HM gametes. Polypropylene filters (100 μm), resulted in effectivecontainment of larvae and settlement larvae, and in this study was not a more effective method ofcontainment than the current on-farm larvae containment protocol. The three obstructive materials wereeffective in containing HM spat, and did not differ in their ability as containment methods.Sodium hypochlorite and Biox™, chlorine-based chemicals, were effective in containing the five life stages ofHM, i.e. sperm, ova, larvae, settlement larvae and spat. The respective life stages were exposed to varyingconcentrations of the respective chemicals (i.e. 10 ppm, 50 ppm and 100 ppm) over five exposure times (i.e.4, 6, 8, 10 and 12 minutes). Sodium hypochlorite and Biox™, at the different concentrations and exposure times, resulted in mortalities in all five HM life stages, with higher incidences recorded at the higherconcentrations evaluated.Future research on the effect of triploid induction on the endocrine system, and how effective gonadmaturation and function is suppressed, needs to be conducted. The aspects of mosaics occurring in induceddiploid animals warrant further investigation with a larger sample size to verify the findings of this study. Theproduction of true sterile individuals would improve the results to use of GM animals as a method ofbiological containment. Incorporation of mechanical containment methods need to be kept in mind whenabalone production systems are designed. The use of chemical containment methods warrants additionalstudies on the practical administration and the economic feasibility of the chemical into the water supply ofopen flow-through abalone culture systems.

[发布机构] Stellenbosch University