Response to salinity challenge in hybrid blood parrot cichlids (Vieja melanura × Amphilophus citrinellus)

Abstract Fishes have repeatedly been introduced into non-native environments around the world, and many of those introductions have come from the pet trade. One of the most important factors that determines the fundamental niche of an introduced fish is tolerance to salinity. Typically, older, larger individuals are more tolerant than younger, smaller individuals. The blood parrot cichlid is an artificially created hybrid ( Vieja melanura × Amphilophus citrinellus ) common in the pet trade. Although cichlids in general are known to be salinity tolerant, one of the blood parrot cichlid’s parental species, the redhead cichlid ( V. melanura ), is only tolerant of low salinity. To better understand how blood parrot cichlids respond to salinity, we performed three experiments that used individuals spanning three different body size classes, and a fourth experiment that included both blood parrot cichlids and individuals of a different hybrid combination: redhead cichlid × Mayan cichlid ( Mayaheros urophthalmus —a species known to be tolerant of high salinity). In chronic exposures, we found that salinity was inversely related to growth rate. In acute exposures, salinity was inversely related to survival. Increased salinity resulted in increases in osmolality of blood plasma, an indicator of osmotic stress. Larger fish generally exhibited higher survival during the salinity challenge. Finally, the redhead cichlid × Mayan cichlid hybrids were more salinity tolerant than blood parrot cichlids. Overall, we found that blood parrot cichlids were salinity intolerant compared to many cichlid species, especially when young, indicating that they would be restricted to freshwater and weakly saline environments if they were to survive in the wild.