Reproductive Biology of the flathead catfish

The following is excerpts from a study by Paul R. Turner and Robert C. Summerfelt over a period of 16 months in 1967-68. It was conducted on Lake Carl Blackwell in Oklahoma.

Sexual maturity of flathead catfish determined by age class was studied. Age IV females were sexually immature. Age class V-VI-VII were found to be sexually mature at rates of 90%-88%-94%. This may indicate that some females may be 10 years or older before reaching maturity.

25% of age class IV were sexually mature and all males age V and older were mature.

Spawning took place when water temperatures were from 24-27 C (75-80 F). Nest sites were secluded rock outcroppings or submerged timber.

This study was the most detailed thesis on catfish reproduction but was correlated by studies conducted by Munger/Wildes/Follis in Texas in 1989. Data also agreed with McKinley and Deacon 1959.

The Texas study was instrumental in regulations in Texas to increase size limits to 24 inches or more for legally kept flatheads. Texas Parks and Wildlife calculated that at 24 inches 84% of flatheads are sexually mature and this would allow sufficient natural reproduction to augment their stocking efforts.

Texas was one of the first states to make serious attempts to hatch and stock flathead catfish. For a period up until 1979 Eggs were collected from the wild or brood fish were allowed to spawn naturally at hatchery sites. Spawning sucess was low and in 1979 Texas experimented with hormone injections to increase spawning success. Injections of HGG improved spawning success and were continued.

I recently corresponded with a Hatchery manager (Ken Neubrand} in Missouri and using the injection techniques on captured flatheads, he has reached very good spawning success. He told me that wild fish caught with limblines incurred less stress than netted flatheads and produced a better spawn.

I have observed that flatheads prefer nesting sites with the best cover they can find to defend the eggs from predation. Holes in the bank such as beaver dens or unedrwater barrels or caves made from large overlapping rocks are preferred. Dense underwater brush that makes it difficult for other fish to get to the eggs are is also a preferred site.

In 1967 45% of the sexually mature female flatheads did not spawn. The ovum were re-absorbed into the fishes bodies. Low LSI and GSI from females which did not spawn indicate that there was a nutrient transfer back to the liver of fish which re-absorb their eggs.

This seems to suggest that females who were not feeding well prior to the spawn had a systemic response to help regulate body weight and liver function. By not spawning they provided their bodies the LSI needed to sustain fat in their bodies and specifically in the liver. If this theory is true then populations of flatheads can vary in their reproductive performance based on their overall health and availability of food. Drought and flood or other adverse conditions that stress the fish will cause a decline in their ability to spawn.

The fact that not all mature females spawn, answered questions I had about fish with eggs in them long after spawning occured. In most states flathead catfish are not stocked so releasing big flatheads is essential to recruitment of the species for the future.

The average number of eggs for all females studied was 1200 eggs per pound. Although the number of eggs per pound decreased as body size increased the percentage of viable eggs increased with body size.

Simply speaking larger females produced more eggs by volume and at a rate that would hatch better than smaller females eggs. This correlates with common reasoning that larger flatheads would produce better spawns. A female of 50 pounds or more might produce a 300,000 to 400,000 eggs with most of them hatching. If 100 of those baby flatheads reach their first birthday it would be considered a very successful spawn.

Also of note:

The picture of the flatheads at 90 days above show the fish confined in a small space. Many states have abandonded attempting to hatch flatheads. One of the reasons is the cannibalistic nature of the fingelings. Vince Travnichek of Missouri said that this problem was easily overcome by keeping their fingerlings fed well.