At all fish densities, the lowest gross conversion efficiency (GCE, DM:DM) was observed when fish were offered 9 RFL (or 81 RFL at 10 fish L−1): these feeding levels largely exceeded the maximal needs of fish (cf. Figs. 6 and 7), so food was inevitably wasted. The highest GCE at all fish densities (about 0.35–0.40) was obtained with the lowest feeding level. However, this finding is not an encouragement
to feeding submaximally the larvae of this species, especially in view of the negative effects of underfeeding on fish growth and survival. Furthermore, the GCEwas almost equally high with other treatments that produced significantly faster growth and higher survival than among groups fed 1 RFL (e.g. 90:3 treatment). The best GCE values during this study were just below those (0.45 DM:DM) obtained in experiments where the growth of cannibalistic larvae of P. hypopthalmus was compared to their actual food intake (E. Baras, unpublished data). This comparison suggests that, in spite
of the apparent simplicity of their foraging behaviour, larvae of P. hypophthalmus are capable of finding and capturing food quite efficiently, even when prey are scarce or just abundant enough to fulfil their needs (Fig. 6).