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The aim of this study was to evaluate the effect of microalgae on the rearing of newborn juveniles of the longsnout seahorse, Hippocampus reidi. Two treatments in three replicates were tested over a 15-day period: with and without the addition of the microalgae Nannochloropsis oculata at a concentration of 2.02 AE 0.44 9 10 6 cells mL À1 . At each replicate, beginning on the second day of life, 120 H. reidi juveniles (stocking density of 3 ind L À1 ) were fed the offspring of the benthic copepod Tisbe biminiensis (100 copepod cm À2 ) together with newly hatched Artemia nauplii (3.8 mL À1 ). From the sixth day of life, enriched Artemia metanauplii replaced newly hatched Artemia nauplii. After 15 days, the H. reidi individuals were counted, measured and weighed. Mean survival was significantly greater in the microalgae treatment (76.42 AE 5.07%) than in the treatment with no microalgae (25.44 AE 6.91%). Moreover, total length, height and dry weight were significantly larger in the microalgae treatment. Thus, the addition of microalgae increases the growth and survival of H. reidi juveniles fed T. biminiensis and Artemia. The higher growth and survival of H. reidi juveniles was not related to the larger ingestion rates but probably to the nutritional improvement of the live feeds or to the probiotic effect. The protocol developed for rearing H. reidi juveniles resulted in a high survival, and represents an advance in the farming of this species.

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