Daniel Jackson

University of Queensland and CSIRO Cleveland

Division of Marine Research, CSIRO, 233 Middle St., Cleveland, QLD 4163

ph. (07) 3826 7240

(07) 3826 7268

email: djackson@zoology.uq.edu.au

The following preliminary results are the product of an ongoing feeding and nutritional study designed to assess the feasibility of growing H. asinina on artificial diets formulated for Australian temperate abalone species. Results from this study will indicate the potential for growing H. asinina on a commercial scale. This work is part of PhD thesis in collaboration between the University of Queensland and the CSIRO Division of Marine Research, Cleveland.

Animals for the trial were selected from a stock cultured on Heron Island and maintained at CSIRO. Animals within the shell length range of approximately 15 to 25 mm were selected and allocated to an experimental unit so that there were no significant differences in size between units. All animals were tagged by gluing a small numbered coloured plastic disc to the shell. Animals were weaned onto the diets for approximately 10 days and acclimated for a further 41 days to reduce the residual effects of body stores accumulated from previous diets. A 'spare replicate' of each diet was also maintained with animals kept under the same conditions as those in the trial. This enabled the replacement of dead animals with similar sized animals of the same nutritional and environmental history. The size and weight of a ‘replacement’ animal was recorded before being introduced to the experiment. Because all animals were tagged, replacement animals could be identified and their growth rates from the time of introduction to the experiment proper could be monitored.

Animals were fed every weekday evening, and uneaten feed is removed every morning. This process is conducted once on weekends. The approximate weight of feed offered (expressed as a percentage of body weight) offered each night are 6% for Gracilaria and 1% for all three artificial diets.

Monthly measurements of growth are taken by measuring shell length (0.05 mm) and weight (0.001g). Observations on gonad development were made from the third month onwards. This was done by pulling down the foot and looking for gonadal tissue. The sex of those animals displaying gonad tissue was determined from the colour of the reproductive tissue. The sex and size at which an animal first displayed reproductive tissue was recorded.

The dry matter of each diet was determined by weighing three replicate samples of each diet into a foil cup, and then drying the samples at 105^oC overnight. The dried samples were cooled in a desiccator, re-weighed and the dry matter calculated.

The water stability of each diet was determined by weighing three replicate samples of each diet into a 5cm length of PVC with 1mm mesh stretched across the bottom, designed to allow water to pass through the container but to retain the pellets of food. In this way a replicate of each diet was kept in a 1.7l Tupperware container (the same as those used in the feeding trial) for 12 hours at 28^oC with a seawater flow rate of approximately 300ml/min. Remaining feed was filtered, gently washed with fresh water to remove salt and dried at 105^oC overnight. The dry weight of the feed retained by the 1mm mesh was calculated as a percentage of the dry weight of the feed before 12 hour immersion. Wet weights were used in the water stability calculations for Gracilaria.

Comprehensive statistical analyses have not yet been performed on the data, but trends are becoming clear (Fig. 1). In terms of growth, FDG is performing at least as well as the natural diet Gracilaria (Table 1). Interestingly there have been five times more deaths on the natural diet compared to the FDG diet (Table 2).

Table 1. Percentage increases in weight and shell length over a 5-month period, and approximate percentage body weight of food fed nightly

Table 2. Mortality on the four diets after 5 months

Analyses of total lipid and total protein content of each of the four diets will be completed in order to further understand the results from the growth trial. A histological analysis of gonadal tissue from animals raised on the artificial diets will give an indication of the viability of gametes produced by these animals. If such an analysis suggests the presence of viable gametes, it may be possible to induce spawning through one of a number of methods described in the abalone literature. If the induction of spawning is successful, and larvae can be reared and settled, it would be the first documented case of the life cycle of H. asinina (and perhaps of any Haliotid) being closed on an artificial diet. This would greatly simplify the aquaculture of H. asinina.

FCRs will also be calculated to gauge the efficiency of each diet. Protocols in place at CSIRO to measure the FCRs of prawn feeds will be modified to fit the current H. asinina system.

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