The effects of protein hydrolysates on the immunity and growth of the abalone Haliotis midae

Dietary hydrolysed proteins have been shown to stimulate the non-specific immunity of various finfish species, whilst the potential for immune stimulation of these feed ingredients in abalone has not been investigated. The immune-stimulating potential of two hydrolysed protein sources (self-prepared fish silage and a commercial fish protein hydrolysate) at two dietary inclusion levels in abalone diets was therefore measured in the South African abalone Haliotis midae, using animals of initial mean weight of 123 g-128 g. Diets containing the high inclusion levels were also fed in two feeding regimes: continuous feeding, or phase feeding, where the hydrolysed protein diets were alternated monthly with the control diet. In low inclusion diets, hydrolysate inclusion contributed 6 g·kg− 1 protein in the final diet, whilst in high inclusion diets this was increased to 18 g·kg− 1. It was found that the low inclusion level of the commercial hydrolysate significantly increased the cellular immunity through increasing the phagocytic activity of haemocytes by 18% compared to the control diet, whilst none of the other diets showed any significant differences compared to the control. Both inclusion levels of the commercial hydrolysed protein significantly improved daily weight increase of animals. Phase feeding had no positive impacts on immunity or production performance. The inclusion of both types of hydrolysed protein sources significantly decreased the water stability of feeds compared to the control, except at the lowest inclusion level of the commercial hydrolysate. It is concluded that the use of dietary hydrolysed proteins can lead to improved cellular immunity and growth in abalone, however it is important to determine appropriate inclusion levels to prevent negative impacts on feed water stability and production performance.