Tolerance and growth of the longsnout seahorse Hippocampus reidi at different salinities

•The tolerance and growth of seahorse Hippocampus reidi to salinities 0-35 psu and isosmotic point was determinated.•The longest LT50 was observed for salinity 10 psu, decreasing at higher salinities. LT50 was shortest at 0 and 5 psu.•Weight and height at 10 days of age decreased with salinity within the interval 10-35 psu.•The isosmotic point of the species was determined as 303.38 mOsm / kg, equivalent to 11.68 psu.•Intermediate salinities therefore offer the best conditions for cultivating this species during the first days of life.

Hippocampus reidi is one of the most popular seahorse species in the aquarium trade. The commercial breeding of this species is an alternative to reducing the fishing pressure on natural populations. Two experiments with newly born juveniles were conducted in this study to assess salinity tolerance (Lethal Time for 50% of the population-LT50), survival and growth during the first 10 days of life. A third experiment determined the isosmotic point of adults. The highest LT50 was observed at 10 psu, followed by 15, 20, 25, 30, and 35 psu, and the lowest LT50 was recorded at 5 psu. A negative relationship between salinity and final weight and between salinity and final height was observed through the regressions performed, such that a decrease in salinity (until the lowest level analysed; 10 psu) implied a higher growth in height and weight. The highest survival rates were observed between the salinities 10 and 25 psu. The isosmotic point of the species was determined at 11.68 psu (303.38 mOsm/kg), which is in agreement with the salinity where the best salinity results were observed in the first two experiments. Using an intermediate salinity to produce H. reidi on a commercial scale would be advantageous because of survival and growth improvement in addition to requiring a lower seawater uptake and less cost for purchase artificial salt.