First development of various vegetable-based diets and their suitability for abalone Haliotis tuberculata coccinea Reeve

Abstract

To date, European abalone aquaculture relies mostly on locally harvested fresh seaweeds which nutritional quality and abundance vary greatly, hence affecting abalone growth. Abalone artificial diets generally include fishmeal, limiting their utilization in ecologically sustainable aquaculture and affecting abalone quality and acceptance by the consumers. A six month feeding trial was conducted to assess the nutritional value of four different dried seaweed meals: Ulva lactuca (Chlorophyta), Gracilaria cornea (Rhodophyta), Laminaria digitata (Phaeophyta) and Palmaria palmata (Rhodophyta), as ingredients to all-vegetable-based formulated feeds for abalone Haliotis tuberculata coccinea (33.1 ± 0.8 mm and 4.7 ± 0.6 g). A mixed fresh algae diet of G. cornea and U. Ulva rigida, reared in an Integrated Multi-Trophic Aquaculture (IMTA) system, served as control. Survival rates were very high (95–98%), regardless of the diet fed. Enriched fresh algae produced a significantly higher growth for H. tuberculata coccinea (169% weight gain) than all the artificial diets (49–84% WG). Comparison among abalone fed the different formulated diets showed that the inclusion of P. palmata improved growth, condition index and dietary protein utilization. On the contrary, the use of L. digitata markedly reduced the efficiency of dietary protein since the protein-related nutritional index (PER), the percentage of protein deposited in the foot muscle as well as the meat to shell ratio recorded for animals fed this diet were the lowest, despite a higher feed intake. Large differences were found in the FA profile of fresh algae as compared with the three formulated diets. The n-3/n-6 ratio was much higher in the fresh algae and, consequently, in the foot tissues of abalone fed this diet in comparison to the one of those fed the formulated ones. The elevated contents of 20:4n-6 in the abalone fed the experimental diets and 20:5n-3 in abalone fed the fresh algae, as well as their respective metabolites, suggest that abalone have the ability to desaturate and elongate LA to ARA and ALA to EPA. Further studies are required to improve the growth obtained with these vegetable based diets, especially concerning the use of different seaweed combinations and inclusion levels, as well as the diet processing methods to improve diet water stability.