Degree-days as a tool to determine the heating requirement for channel catfish spawning in earthen ponds

Temperature and time are critical in determining when channel catfish Ictalurus punctatus will be physiologically ready to spawn (conditioned). Natural and hormone-induced spawning can occur when the fish are held at, above, or below specific temperatures for a largely undetermined minimum period of time. This period of conditioning can also be described as the heating requirement for spawning. We used degree-days as a standard unit to describe and quantify the heating requirement for channel catfish spawning, and we developed specific terminology and standard parameters to support the use of the degree-day concept for channel catfish spawning. The heating requirements for spawning were quantified by (1) retrospectively calculating degree-day values using previously collected data (2000-2003) from heated and ambient-temperature ponds before and during the natural spawning season and (2) calculating degree-days using data from fish conditioned for the 2004 natural spawning season at different thermal regimes in heated ponds at three threshold temperatures. These results were used to calculate spawning probabilities to enable future spawning predictions using degree-days. The values calculated using the 21 degrees C threshold were more consistent than those calculated using the two other thresholds: 18 degrees C and 24 degrees C. The heating requirements for spawning in heated ponds before the natural spawning season were not different from the requirements for spawning in ambient-temperature ponds during the natural spawning season. Degree-day guidelines for channel catfish spawning were proposed based on the results of the degree-day calculations and spawning probabilities using a commercial definition that corresponded with the 21 degrees C threshold. According to those guidelines, channel catfish spawning can begin in 0.04-ha ponds in southern Louisiana after the accumulation of 57-172 degree-days, with a median value of 99 degree-days.