A first study on the effect of dietary soya levels and crystalline isoflavones on growth, gonad development and gonad histology of farmed abalone, Haliotis midae

Abstract

Soya in formulated diets for abalone, Haliotis midae, can improve somatic growth. However, it may also influence gonad development, thereby limiting the potential benefit of including soya in feed. This is the first study to determine both the effect of dietary soya level on growth and reproduction of abalone and the role of crystalline isoflavones (ISO) at concentrations occurring in soya diets. Abalone (40–50 g individual−1) were fed seven isonitrogenous and isoenergetic diets. Three diets contained 5, 10 or 19% soya, while an additional three diets included graded levels of ISO. A fishmeal (FM)-only diet was included. The inclusion of ISO did not influence gonad development or abalone growth while soya inclusion level had an effect on both reproductive development and abalone growth. After 180 days, male abalone fed FM with soya inclusion had the highest whole body mass (69.0 ± 2.48 g abalone−1), meat mass index (60.5 ± 1.88%), visceral mass index (13.0 ± 0.27%) and gonad bulk index (42.7 ± 9.82 g abalone−1). Weight loss was observed in all treatments probably due to spawning events. The frequency distribution of the predominant oocyte stage, stage 7 was influenced by soya concentration. The increase in the frequency of stage 7 oocytes in abalone fed FM with soya did not reduce the number of oocytes (45.0 ± 3.01 oocytes mm−2), while the number of oocytes (o) in abalone fed the FM-only diets decreased with increasing abundance of stage 7 oocytes, possibly due to an increase in oocyte size.