DIGESTIVE EFFICIENCY OF THE AUSTRALIAN ABALONE HALIOTIS-RUBRA IN RELATION TO GROWTH AND FEED PREFERENCE

The digestibilities of dry and organic matter, energy and nitrogen were determined for Haliotis rubra feeding on a range of monospecific algal diets. These digestibilities, in conjunction with total intakes, were used to estimate the daily intakes of nitrogen and energy of abalone feeding on those algal species used by Fleming (1995). These were then used to explain the growth rates, intakes and chemosensory preferences of abalone in that study. The chemosensory preferences of abalone were strongly related to the digestible nitrogen content of the algae and to a slightly lesser extent the nitrogen content of the algae, indicating the important role nitrogen plays in setting preferences in this abalone. The intakes of digestible nitrogen were significantly related to the growth rates of abalone, suggesting that nitrogen is a limiting nutrient to abalone growth, Thus, N. rubra selects those foods which maximise the intake of nitrogen and result in maximum growth rates. Energy does not appear to play a major role in setting abalone preference as the digestible energy contents of algae in this study (and in general) are similar and did not correlate with preference. The digestible nitrogen content was lowest in the 3 brown algae tested and digestibility was related to the polyphenolic content of the brown algae. This suggests that the low growth of H. rubra on these species results from the action of polyphenolic compounds, reducing nitrogen digestibility.