SALINITY EFFECTS ON PHYSIOLOGICAL RESPONSES IN HYBRIDS OF MEXICAN, MAYAN AND MIDAS CICHLID HYBRIDS Cichlasoma synspilum, C. urophthalmus, AND Amphilophus citrinellum

Success of invasive fish species to adapt into new environments depends on their tolerance of variable salinity, and non-native cichlids in Florida are a prime example of such challenges. However, because hybridization among cichlids is not uncommon we investigated salinity tolerance among Central/South American cichlid hybrids (Fig.1). A series of experiments assessing both chronic and acute salinity tolerances of different juvenile stages of two hybrid cichlids were conducted.

In the first series of experiments, Mexican x Midas cichlid hybrids, commonly called blood parrot cichlid, were subjected to salinities ranging from 0-28 ppt at three different body sizes (0.09g, 2.0g, and 19.4g) for three weeks followed by an acute challenge. Survival, growth, and feed conversion were recorded throughout all chronic experiments. Blood plasma osmolality and hematocrit were analyzed during experiments where fish size allowed for collection of blood.

A final acute salinity challenge of Mexican x Mayan hybrids and blood parrot cichlid was conducted to compare the salinity tolerances of both hybrid offspring by increasing salinity every 24-h from 0ppt to 20ppt, then to 30ppt, and finally to 35ppt. Blood parrot cichlids experienced loss of equilibrium leading to mortality following the increase to 30ppt at 27-hrs. Although blood plasma osmolarity was significantly higher 24-h after increasing to 35ppt in challenged Mexican x Mayan hybrids (385±29 mOsm) compared with controls (327±4 mOsm), no mortality occurred throughout the 72-h trial. This indicates that Mexican x Mayan hybrid cichlids inherited salinity tolerance from Mayan cichlid and in comparison to blood parrot cichlids could pose an increased risk of invasion of both fresh and estuarine environments.