Effect of Salinity on Hatching in Neobenedenia melleni, a Monogenean Ectoparasite of Seawater‐Cultured Tilapia

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Abstract
Laboratory experiments were conducted to determine the effect of salinity on embryonic development and hatching in Neobenedenia melleni, a monogenean ectoparasite of seawater‐cultured (37 ppt) Florida red tilapia (Oreochromis urolepis hornorum × O. mossambicus). Eggs, collected from adult monogeneans at 37 ppt, were exposed to different salinities (0, 6, 12, 18, 24, 30 and 37 ppt) for 48, 72 or 96 h. Varying degrees of post‐treatment development and hatching occurred when natural seawater conditions were restored. Hatching success generally declined with decreasing salinity and increasing duration of exposure. Under all durations of exposure, hatching success remained relatively high (≥ 69.6%) at salinities of 24 ppt and above, but declined markedly (≤ 32.5%) at lower salinities. Hatching did not occur in eggs exposed to fresh water (0 ppt) for 72 and 96 h. The most effective treatments in preventing hatching, other than prolonged exposure to fresh water, were 96 h exposures to low‐salinity brackish water. Percent hatch after 96 h exposure to 6, 12 and 18 ppt was 5.5, 11.9 and 5.8%, respectively.