Growth performances and natural diet of European eel (Anguilla anguilla L.) reared in muddy and sandy ponds

This study evaluated the growth performance and survival rate of Anguilla anguilla glass eels reared in 4750 m2 earthen ponds and dependent on trophic resources provided by natural macrobenthic populations. Two ponds (M ponds) had mostly muddy-soil bottom whereas the other two (S ponds) had mostly sandy-soil bottom. A total of 4795 pigmented glass eels (0.73 ± 0.26 g) were stocked, at a density of 1.6 fish/m2. After 360 days of growth, in S ponds eels exhibited a final mean body weight (15.57 ± 5.36 g) significantly higher than those seeded in M ponds (9.85 ± 4.11 g). Mean final length of S eels (21.55 ± 3.33 cm) was statistically higher than that of M eels (17.85 ± 2.42 cm). In M ponds, relatively higher abundances of Crustacea appeared to promote higher survival of glass eels in the post-seeding phase. Consequently, the relatively higher densities of eels in M ponds could have resulted in slower growth compared to eels in S ponds; however, eels grown in M ponds exhibited a significantly higher conditioning factor at the end of the growth period. We conclude that M ponds host highly viable macrobenthic prey populations that better sustain the early growth phases of A. anguilla. Furthermore, this study demonstrated that artificial feed supplements are not necessary for the rearing of A. anguilla juveniles in earthen ponds