LIGHT AND DIETARY EFFECTS ON SHIFT FROM PLANKTONIC TO BENTHIC BEHAVIOR OF JUVENILE SEAHORSE Hippocampus reidi

Newborn seahorses were  transferred to  acrylic pseudo-kreisels (10L each) connected  to a recirculation system (500L). Temperature, pH, salinity , ammonia and nitrite were maintained at 25ºC, 8.2, 27ppm and 0.0ppm, respectively. Photoperiod was 10L:14D. Newborns w ere fed three times a day with  five different treatments, four of them : Artemia nauplii enri ched  with different emulsions (one high-cost commercially available and three low-cost obtained from natural products) and a control group was fed  with Artemia nauplii without enrichment only. S eahorses were categorized  as benthic when they  were holdfast attached to substrates . Observations were made twice a day, the first before turning on the lights (scotophase) and the second before turning the lights out (photophases) . Differences in settlement rate  were  statistically  analyzed with Wilcoxon test to compare dark and light photoperiod, and Friedman test to compar e experimental groups. Additionally, bromatological analysis and fatty acid profile of the tested food groups was performed.

Seahorses started to settle at day 7 and had a progressive increase in settlement rate from day 13 on.  There was difference regarding  settlement rate among the feed treatments. S eahorses fed with enriched treatments had good results compared to without enrichment group (Friedman: p<0,05). The lipid and fatty acid profile of enriched treatments revealed also marked differences than without enrichment group (data not shown). There was also a higher number of settled juvenil es on dark period (Wilcoxon : p<0,05) , in all experimental groups  compared to light period.

Knowing that  H. reidi is a visual daytime predator, we conclude that the photoperiod and adequate nutrition contribute positively to establishment of settlement behavior, considering that such transition occurs in a longer period for H. reidi comparing to other seahorse species.