Long-term patterns in inland fish kills associated with cold-shock and winter stress: a regional case study from Texas.

Colder water temperatures are generally regarded as a stressful period for fishes (i.e., winter stress syndrome), which can be exacerbated by cold-shock stress associated with major arctic freezes. Although cold-shock stress and mass mortalities are well documented for coastal marine fishes, few studies report the effects of winter stress or cold-shock stress on inland fishes. The purposes of this study were to describe patterns in inland fish mortalities associated with winter stress syndrome and with cold-shock stress in Texas as a regional example of inland fish mortalities associated with colder water temperatures. Using fish mortality reports (1969-2021) recorded by state agency biologists, colder water temperature mortalities occurred in 66% (N = 35) of the years, with greatest percentages of the reports occurring during three major arctic freezes in 1981, 1983 and 2021. The majority of reports were from urbanized counties (79%) and from lentic habitats (56%). Seventeen taxa and 1,021,217 individuals were estimated to be killed during the 53s years. Numbers of inland fish mortalities were greater during major arctic freeze years than non-major arctic freeze years, attributed primarily to mortalities of non-native fishes (e.g., blue tilapia Oreochromis aureus, suckermouth catfish Hypostomus plecostomus). Numbers of native fish mortalities, primarily clupeids and catostomids, were not different between major arctic freeze years and non-major arctic freezes. The 43,000 inland fish mortalities reported during major arctic freeze years are in stark contrast to the 35 million coastal marine fish mortalities. Proposed mechanisms to explain cold-shock mortalities in coastal waters (e.g., species within the northern extent of their range, lack of access to deeper water) are similar in inland waters, yet inland waters do not have the same level of mortalities. Consequently, the disparities between mortalities in coastal and inland waters are not readily discernable at this time.