The effect of macroalgal, formulated and combination diets on growth, survival and feed utilisation in the red abalone Haliotis rufescens

Abalone aquaculture in Chile is dominated by production of the red abalone Haliotis rufescens using a diet comprised predominantly of fresh, wild-harvested macroalgae. Concerns over the long-term supply of macroalgae have led farmers to investigate the suitability of various formulated feeds, however there has been limited commercial adoption. Combination diets of macroalgal and formulated feed fed together provide a mechanism to explore and adapt to formulated feed use without entirely abandoning macroalgal feed. The current study evaluated the use of formulated, macroalgal and two combination diets (low and high macroalgal supplementation) on production indicators and canning yields of juvenile abalone H. rufescens in a culture system modified for formulated feed. The macroalgal diet and the high macroalgal-formulated pellet combination diet (76.1% macroalgae: 23.9% pelleted diet as dry weight) produced significantly higher growth indicators (SGR and LGR) than the low macroalgal-formulated pellet combination diet (31.6% macroalgae: 68.4% pelleted diet as dry weight) and the formulated pellet diet. The protein efficiency ratio of the experimental treatments was positively related to the proportional contribution of fresh macroalgae in the diet. Furthermore, calculation of the protein efficiency ratio of the formulated component in combination diets (PERf) revealed a significant positive relationship between macroalgae contribution and PERf. This suggests that the increase in total PER is driven by the increased utilisation of protein in the formulated component of combination diets associated with increasing levels of fresh macroalgal supplementation. We suggest possible reasons why the presence of seaweed increased the availability of the formulated feed protein to the abalone. A simulated canning trial highlighted a significant positive linear relationship between meat canning yield and the proportional contribution of formulated feed. This study highlights the value of combination diets as a tool for abalone producers to harness the potential production advantages of macroalgae while still accessing the processing benefits associated with nutrient dense formulated feed. Statement of relevance: We believe that this manuscript describes novel insights into the efficiency of protein utilisation in juvenile red abalone fed combination diets as well as the effect of diet, particularly formulated feed inclusion level, on canned meat yields. This provides empirical information to inform commercial abalone farmers of H. rufescens when exploring dietary options for optimal culture. (C) 2015 Elsevier B.V. All rights reserved.