Warmed Winter Water Temperatures Alter Reproduction in Two Fish Species

Area of Science:

• Environmental Science
• Aquatic Ecology
• Ecotoxicology

Background:

• Anthropogenic activities, such as thermal pollution from industrial or municipal effluents, can significantly alter natural winter water temperatures in streams.
• These altered thermal regimes may impact the reproductive cycles of resident fish populations, potentially leading to ecological disruptions.

Purpose of the Study:

• To investigate the effects of elevated winter water temperatures on the spawning success of Fathead Minnows (Pimephales promelas) and Johnny Darters (Etheostoma nigrum).
• To assess the role of vitellogenin expression as an indicator of reproductive readiness in fish exposed to thermal pollution during winter.

Main Methods:

• Fathead Minnows and Johnny Darters were exposed to various winter water temperatures (4°C to 20°C) simulating natural and thermally impacted conditions.
• Spawning success was monitored, and egg production was assessed during simulated spring transitions.
• mRNA expression of vitellogenin, an egg yolk protein, was analyzed in female Fathead Minnows to gauge reproductive status.

Main Results:

• Fathead Minnows spawned at 16°C and 20°C in winter, but not at 12°C. Spring spawning was delayed in fish overwintered at 16°C and 20°C.
• Johnny Darters spawned in winter at 12°C, 16°C, and 20°C, but not at 4°C. Those at 4°C spawned in spring, while those at warmer temperatures did not.
• Elevated winter temperatures led to increased vitellogenin expression in female Fathead Minnows, indicating preparation for spawning.

Conclusions:

• Elevated winter water temperatures, characteristic of effluent-dominated streams, can induce premature or out-of-season spawning in Fathead Minnows and Johnny Darters.
• Vitellogenin expression serves as a reliable biomarker for assessing the impact of elevated winter temperatures on fish reproductive readiness.
• The findings highlight potential ecological consequences of thermal pollution on fish reproduction and population dynamics.