The life history responses of the abalone pest, Terebrasabella heterouncinata, under natural and aquaculture conditions
- Authors: Simon, Carol A , Kaiser, Horst , Britz, Peter J
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6773 , http://hdl.handle.net/10962/d1008074
- Description: The sabellid, Terebrasabella heterouncinata, is a small (<5 mm) intratubular brooder that lives in burrows within the host s shell matrix. It is a semi-continuous breeder and despite producing small numbers of large eggs, infestation by this animal has reached epidemic proportions on local abalone farms. The present study compared the morphometrics and reproductive characteristics of worms from farmed and wild abalone, in the Walker Bay area of the south Western Cape Province of South Africa, to gain insights into why this animal has become so successful under aquaculture conditions. The farms designated farm A and farm B each had one on-farm site, and two wild sites, while farm C had two on-farm sites and two wild sites. The wild sites were natural abalone habitats located within 2.5 km of the farms. Our results conclusively showed that environmental conditions prevalent on the farms enhanced the reproductive success of these worms relative to that observed in its natural environment. At farms B and C, worms occurred in significantly higher densities at the on-farm sites than in the corresponding wild samples, but at farm A, density was equally low at the three sites. At all three farms, a greater proportion of the population was reproductively active in the on-farm samples than in the wild samples. Worms on farmed abalone had a higher instantaneous fecundity, brooded more clutches simultaneously and were larger than their conspecifics from the wild. There was a positive correlation between adult size and brood size and the number of clutches brooded simultaneously. Within the three on-farm sites there was a negative correlation between egg volume and brood size, indicating a trade-off between these traits. However, such a trade-off was not apparent between sites, with brood size being higher at the on-farm sites than at the wild sites, irrespective of egg size. This suggests that the stable nutrient-enriched environment on the farm led to an increase in fecundity without compromising the size (and implicitly the quality) of the eggs. Worm density did not have a significant effect on body size or any other reproductive traits at most sites, and the density of T. heterouncinata was unaffected by the density of other shell-infesting polychaetes. The results suggest that the farm environment has selected for larger, more fecund worms that breed rapidly with high recruitment success as a consequence of abundant nutrients, high host density, habitat stability and a possible lack of predation and interspecific competition.
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- Date Issued: 2005
An assessment of the efficacy of two lysine microencapsulation techniques to determine the quantitative lysine requirement of the South African abalone, Haliotis midae L
- Authors: Shipton, Thomas A , Britz, Peter J , Walker, Roderick B
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184289 , vital:44197 , xlink:href="https://doi.org/10.1046/j.1365-2095.2002.00204.x"
- Description: The quantification of the essential amino acid requirements of a species is a prerequisite to the formulation of biologically optimized diets. In this study, crystalline L-lysine was used in an attempt to determine the quantitative lysine requirement of juvenile Haliotis midae. Two microencapsulation techniques [gelatine/acacia and cellulose acetate phthalate (CAP)] were used to retard leaching of crystalline L-lysine incorporated into semipurified test diets. An assessment of the efficacy of the encapsulation techniques, revealed that despite effective lysine supplementation, H. midae fed semipurified test diets containing encapsulated crystalline L-lysine failed to promote significant improvements in either growth, feed or protein efficiency (P > 0.05). The failure of the crystalline L-lysine to illicit growth and nutritional responses is discussed.
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- Date Issued: 2002