Infestation of the abalone, Haliotis midae, by the sabellid, Terebrasabella heterouncinata, under intensive culture conditions, and the influence of infestation on abalone growth

Abstract

Heavy infestation by the shell-infesting sabellid, Terebrasabella heterouncinata, has been shown to cause a reduction in the growth rate and marketability of cultured abalone. This worm is endemic to South Africa and the locally cultured abalone, Haliotis midae, are under constant threat of infestation. An understanding of factors that influence abalone growth and sabellid infestation levels under intensive culture conditions is therefore imperative to controlling infestation levels. Abalone were held on an abalone farm at stocking densities of 18%, 23% and 28% of the surface area available to the abalone. They were fed kelp or a pelleted diet, Abfeed™. Their growth and infestation levels were monitored for 14 months. Within the range of abalone sizes used for this study kelp-fed abalone grew significantly better than Abfeed™-fed abalone ( F 1,197=7.99; P≤0.005), while stocking density had no effect ( F 2,196=1.41; P≤0.246) on growth. Abalone that became infested grew at the same rate as those that did not (0.09≤ P≤1). No growth-limiting effect of infestation was detected. There was no effect on total intensity (i.e., the total number of worms per sample of 60 abalone; 0.41≤ P≤1 and 0.17≤ P≤1), or prevalence (i.e., the percentage of infected abalone within a sample; 0.50≤ P≤1 and 0.19≤ P≤1) of infestation by diet and stocking density, respectively. There was a significant positive coefficient of correlation of 86.2% between the level at which an increase in total intensity starts, and the average increase in total intensity per day ( F 1,10=62.2; P≤0.0001). A regression model is presented to estimate total intensity based on prevalence. The greatest increase in total intensity levels coincided with the onset of spring, and a possible seasonal component to the reproduction of this sabellid is discussed.