Effects of fluctuating temperatures and gill parasites on reproduction of the fountain darter Etheostoma fonticola

We assessed the effects of fluctuating temperature and gill parasitism on egg and larval production of the endangered fountain darter (Etheostoma fonticola). Fountain darters, with and without the exotic digenetic trematode Centrocestus formosanus, were exposed in the laboratory to constant (24 degrees C) and fluctuating (24 to 26 degrees C, 26 to 28 degrees C, and 28 to 30 degrees C) water temperatures for 21 d. No differences were detected between the number of eggs produced (P = 0.78) or number of larvae produced (P = 0.11) between fountain darters with and without trematodes. Total egg production was greatest at 24 degrees C and decreased (P < 0.05) by 42% at fluctuating temperature of 24 to 26 degrees C, 65% at fluctuating temperature of 26 to 28 degrees C, and 99.6% at fluctuating temperature of 28 to 30 degrees C. Likewise, larval production was greatest at 24 degrees C and decreased (P < 0.05) by 63% at 24 to 26 degrees C, 99.9% at 26 to 28 degrees C, and 100% at 28 to 30 degrees C. Water temperature (24 to 26 degrees C) that fluctuated within previously considered optimum temperature (< 27 degrees C) reduced the number of eggs and larvae produced by the fountain darter. Results of this study refined maximum optimum temperature requirements of the fountain darter reproduction with water temperatures >= 26 degrees C reducing egg production and water temperatures >= 25 degrees C reducing larval production.