The most important reason for aquaculture is profit. To achieve this at South Australian Abalone Developments in the shortest time possible the stock require a very high nutritional diet. This diet should be of a high quality resulting in the stock gaining weight and size over the shortest time for as little cost as possible. Yet to obtain a high quality nutritional diet for abalone the financial cost can be a little high. Therefore it must be assessed whether growth and weight gain is sufficient to justify a high priced food.

Over the past few years South Australian Abalone Developments has been purchasing the artificial abalone diet from two companies, Adam and Amos and Gulf Feeds. No specific growth trials have been performed with appropriate data recordings comparing the diets these companies offer. Gulf Feeds offer quite cheap diets, whereas Adam and Amos offer high quality nutritional diets at a higher expense. With recent misfortunes and the company wanting to minimise costs it has been necessary to assess which of the abalone artificial food companies offered the best value for money diet. Knowing the Summer diet that both of these companies offered was their highest quality diet it was decided that this diet should be trialed for the comparison of the best value for money diet.

As there is no real data available for specific diets relating directly to the unique growout facility that South Australian Abalone Developments has, the main aim of this trial was determine which diet produces the best gains in growth and weight over a four week period and whether the cost of the food was justified by these advances in size and weight. The palatability and suitability of the feeds for the animals and raceways were also assessed. For statistical analysis we can hypothesise that the whole weight gain and shell size increase should be equal between the animals being fed the Summer diets supplied by the two different companies, Adam & Amos and Gulf Feeds.

For each of the raceways a random sample of 100 animals was removed and the average whole weight taken. Then each individual abalone had the shell size measured using callipers and then the average shell size was recorded. Each random sample of abalone were then placed back into their raceway. The whole body weight for each raceway was calculated and then used to find the amount of feed that was to be fed to each raceway each day. This was done by taking the average weight of the animals in the he raceway and multiplying it by the number of animals in each raceway. At the beginning of the trial 2% of the total whole body weight was fed each day. Prior to being fed the raceways were cleaned and mortalities removed and the total number of animals per raceway recalculated. It was found after a week or so there was too much food being left and not being eaten so the percentage of food being fed in relation to the total body weight per raceway was reduced to 1% per day.

At the end of the four week trial period, a non-biased random sample of animals was taken from each raceway weighed and measured to get the average shell size and average whole weight. These results were then taken and compared to the data collected at the beginning of the trial to compare the two diets trialed. A 1-way analysis of variance was used to assess the difference between the two diets for both whole weight gain and shell size gain.

Throughout the period of the trial water parameters such as pH, dissolved oxygen and temperature were recorded.

From Table 1 it is clearly visible that the Adam and Amos diet has increased the shell size and whole weight significantly compared to the Gulf Feeds diet. The averages indicate that there was a 1.7 gram difference between the two diets in favour of Adam and Amos's Summer mix. Similarly there was a 2.3mm difference in the average shell size between the two diets the companies supplied once again in favour of Adam and Amos's Summer diet mix. The abalone fed the Adam & Amos diet grew on average approximately 260um per day, where as the abalone fed with the Gulf Feeds diet only grew on average approximately 183um per day.

From the results it is clearly evident that the Adam & Amos Summer diet was the more nutritional and beneficial diet for the farmed abalone stock. The average gain in shell size over the four week trial period for the stock fed with the Adam & Amos Summer diet exceeded the animals fed the Gulf Feeds Summer diet by 2.3mm or 77um per day. Similarly the whole weight gain for the four week trial period was in favour of the Adam & Amos diet with the animals fed with this diet gaining an average 1.7 grams more whole weight than the abalone fed with the Gulf Feeds diet.

Yet the statistical analysis revealed that there was no significant difference in the whole weight gain over the trial period and that the null hypothesis that the whole weight gain over the four week trial period would be equal between the abalone fed the two Summer diets supplied by Adam & Amos and Gulf Feeds. But the null hypothesis was incorrect for the shell size gain to be equal over the trial period, as the statistical analysis revealed that there was a significant difference between the amount of shell growth throughout the trial between the two diets. It could be speculated that there would be a significant difference between both whole weight gain and shell size if the trial were held over a longer period of time.

The results also indicate that there was a slightly higher percentage of mortalities for the animals fed the Adam & Amos diet than those fed with the Gulf Feeds diet. This is due to two reasons. Firstly the raceways that the Adam & Amos Summer diet was fed to had quite a few more animals in them. Yet it must be understood that the raceways were stocked correctly and that the number of animals for a raceway to be stocked correctly does have a range. Secondly the raceways with the abalone fed the Adam & Amos diet were without water for a short period of time one day at the beginning of the trial due to an inlet pot blockage and hence a few mortalities resulted for a couple of days after the incident had occurred.

The pH, salinity and dissolved oxygen remained at stable and acceptable levels throughout the trial and hence should not have influenced the results significantly. Yet the temperature did vary quite a bit over the trial period with it slowly decreasing as we approached our Winter season. As the temperature decreased over the trial the animals lost their appetite a little and hence the percentage of food to whole body weight for each raceway had to reduce slightly every now and then so there would not be too much of the two Summer diets wasted.

Table 1: Average whole weight and shell size gain over a four week period.

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