Implications of physical key factors in the early rearing of the long-snouted seahorse hippocampus guttulatus

Abstract

Although breeding conditions are rather well established for some seahorse species (Hippocampus spp.), zootechnics and the effect of non-biological factors are still unknown for many species. The present study is focussed on the effects of aquarium type/design, photoperiod regime and aeration level on the early performance (growth and survival) of Hippocampus guttulatus juveniles. Three aquarium types were evaluated: pseudoKreisel, spherical and rectangular. Juveniles grown in pseudoKreisel aquaria showed lower growth rates but significantly higher survivals (69 ± 15%) at day 30 after male's pouch release (DAR) when compared to either spherical (30 ± 22%) or rectangular (16 ± 12%) aquaria. Survival enhancement in pseudoKreisel aquaria was mainly related to the very lower proportion of juveniles showing swim bladder hyperinflation during the first days of life. Conversely, the other aquarium types did not avoid juveniles to remain near water surface and to gulp air in excess for swim bladder inflation. The effects of light regime and aeration level were assayed in H. guttulatus juveniles reared in all three aquarium types or in pseudoKreisel aquaria only, respectively. In general, the application of extended (continuous light) or natural photoperiods (day–night cycle; 16 h light:8 h dark) did not affect survival nor growth significantly. On the other hand, aeration levels in pseudoKreisel aquaria significantly affected juvenile survival. Survivals in 30 day old seahorses reared under a strong aeration were significantly higher (41 ± 12%) than when reared under weak aeration (13 ± 0%). Strong aeration levels enhanced the distribution of juveniles in the aquaria and diminished both their over-exposition to water surface and the resulting appearance of hyperinflation problems. The overall results suggest that the best rearing conditions were met when H. guttulatus juveniles grew in pseudoKreisel aquaria under both a strong aeration level and, to a lesser extent, a natural photoperiod regime, due to a slight enhancement in seahorse juvenile performance