In west Alabama, catfish producers routinely face the challenge of fish that exceed market size (aka “big fish”) in their commercial ponds. These fish are evading harvest and can increase in size significantly before the next harvest occurs. This is a problem because processing plants prefer catfish in the range of 1-4 lbs. Once over this range, processing plants are forced to hand-fillet fish versus using the automated methods that are more cost-effective and are stuck with the additional task of finding a market for these larger fillet products. This leaves the farmer receiving a lower price per pound or oftentimes no financial return for fish found above the premium size. The cost of resources that went into feeding and caring for that fish for an added amount of time, sometimes for several years, must also be factored in. Harvesting inefficiencies and ponds with uneven bottoms that allow catfish to escape seines are major drivers of the big fish problem. Due to their larger size and growth potential, hybrid catfish (Ictalurus punctatus ? x Ictalurus furcatus ?) tend to be a greater big fish issue than channel catfish. Little is known regarding the age structure and growth rates of hybrid catfish that repeatedly evade capture and remain in commercial ponds for extended periods.
The objective of our study is to quantify the age structure and growth of hybrid catfish that evade capture and remain in ponds following commercial harvest. Twelve ponds that have recently been harvested will be sampled to collect up to 100 fish per pond using an electrofishing boat with dip nets. Study ponds will be sampled by researchers before being restocked with a subsequent crop of fingerlings. A very low pulse rate is documented as most effective for sampling large catfishes, with numerous studies backing up low-frequency electrofishing (LFE), in pulsed-DC as the best method for collecting blue catfish. Following collection, fish will be numbered, and the total length (mm), weight (kg), and sex of fish will be recorded. We will extract otoliths from the brain cavity and use the cut method to estimate fish age. This method involves cleaning the otolith of any brain matter, embedding the otolith in a clear epoxy resin, and cutting into it with an IsoMet low-speed precision saw to reveal the core and annuli (annular growth “rings”). Once we can accurately observe the core, we will use Jenoptik Gryphax, a high-quality image analysis software program connected to a microscope, to count the rings surrounding the core. This counting will be conducted by two readers independently and compared. If there is any dispute regarding age, a third reader will be brought in to resolve the disagreement. Data collected on fish age, growth, and longevity of hybrid catfish found in ponds following harvest will help producers and researchers better understand the big fish problem. Additionally, looking at factors like seining frequency and pond characteristics will contribute to solutions for the big fish issue. This study is currently in the data collection phase.