Regional Assessment of Inland Fish Mortalities Associated with Winter and Cold-shock Stresses




Lopez, Steven G.

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The winter is generally regarded as a stressful period for ectothermic animals (i.e., Winter Stress Syndrome), which can be exacerbated by cold shock stress associated with major arctic freezes. Although loosely defined, major arctic freezes consist of abnormally colder air, and therefore abnormally colder water temperatures, for several days (e.g., 2021’s Winter Storm Uri). During major arctic freezes in the 1980s and in 2021, 35 million Texas marine and estuarine fishes were killed attributed to cold shock stress. Interestingly, few studies report the effects of winter stress or cold shock stress on fishes in inland waters. Purpose of this study was to describe patterns in cold weather fish mortalities attributed to winter stress and cold-shock stress within inland waters of Texas between 1969 and 2021 using records contained within Texas Parks and Wildlife Department’s Pollution Response Inventory and Species Mortality (PRISM) database. Among 53 years, reports of cold weather inland fish mortalities occurred in 66% of the years with greatest percentages of the reports occurring during three major arctic freezes in 1981, 1983, and 2021. Majority of the reports were from urbanized counties (79%) and from lentic environments (56%). Sixteen taxa and 1,000,000 individuals were reported killed during the 53 years. Numbers of inland fish mortalities were greater in years with major arctic freezes than in years without major arctic freezes, 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 years with and without major arctic freezes. The 43,000 inland fish mortalities reported during the three major arctic freezes are in stark contrast to the 35 million marine and estuarine fish mortalities. Proposed mechanisms to explain cold shock mortalities in coastal environments (e.g., species within the northern extent of their range, lack of access to deeper water) are similar in inland environments, yet inland environments do not have the same level of mortalities. Consequently, the disparity between mortalities in coastal and inland environments are not readily discernable at this time.



Cold shock, Winter stress, Fish, Fish kill, Winterkill, Cold stress, Texas


Lopez, S. G. (2022). <i>Regional assessment of inland fish mortalities associated with winter and cold-shock stresses</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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