Impact of nine macroalgal diets on growth and initial reproductive investment in juvenile abalone Haliotis tuberculata

The commercial culture of Haliotis tuberculata has recently started in Europe. As abalone is herbivorous, the use of local collected algae as feed may appear advantageous. The nutritional value of eight monospecific seaweed diets was studied using Palmaria palmata (Rhodophyta), filamentous algae, mainly Gracilaria sp. (Rhodophyta), Enteromorpha sp. and Ulva lactuca (Chlorophyta), together with Saccharina latissima, Saccorhiza polyschides, Laminaria digitata and Laminaria hyperborea (Ochrophyta, Phaeophyceae) and a mixed macroalgal diet. An integrative approach consisted in monitoring the seasonal composition changes of these algae in terms of protein, lipid, soluble carbohydrate, fatty acid and amino-acid contents, and to relate it to seasonal growth and reproduction investment during a large-scale experiment. Abalone and algae were studied for one year in commercial sea-cage structures. Abalone fed with monospecific diet using either P. palmata or S. latissima, and with mixed diet presented the best growth rate, muscle ratio and gonad development. Seasonal daily weight gain was mainly associated with n-3/n-6 ratio, soluble carbohydrate content and total protein content. In term of amino-acid contents, the daily weight gain was associated with free phenylalanine as well as isoleucine levels. Moreover, 90% of 2-years old abalone started gonad development but less than a quarter featured a fully matured gonad. The gonad development of H. tuberculata was mostly associated to total valine, methionine, leucine, arginine and isoleucine levels. The age of initial sexual maturity in H. tuberculata turned to be a highly plastic trait in response to different growth rates and algal diets. Even if P. palmata is the best option for growth performance, mixed diets should probably be preferred to a monospecific diet in order to avoid too high pressure on a single algal resource.