Charles Lutz | 10/4/2004 4:24:34 AM
This year, catfish spawning may begin as early as April in Louisiana. Larger and older fish usually spawn first. Early in the season, eggs take longer to develop as the result of cooler water, so spawning cans can be checked at 4- to 5-day intervals without losing newly hatched fry into the brood pond. The onset of a sudden cold front, however, can create serious problems for early spawns since colder water encourages fungal outbreaks on egg masses. Early in the season, cans should be checked whenever the water temperature drops sharply to save recently laid eggs, which are often abandoned under these conditions. To avoid these problems, many producers wait until water temperatures remain above 70°F (21°C) for three nights in a row before putting out spawning cans.
As the season progresses, the smallest and youngest fish are usually the last to spawn. As water temperature increases, the time interval between egg laying and hatching becomes much shorter, and cans should be checked more frequently, at least every three days. Warmer water decreases the risk of fungus but increases bacterial infections of egg masses. Warm water also increases the probability of brood fish infecting their eggs with channel catfish virus.
As egg masses are collected from spawning cans in brood ponds, a laundry basket with floats will provide better water circulation than a washtub or bucket. Egg masses should be transported to the hatchery in water from the brood pond. Aeration must be provided during egg transport; an airstone supplied with compressed oxygen works well.
At the hatchery, eggs should be dipped in an iodine solution following label directions, for 5 to 10 minutes. Never bring eggs beyond the door of the hatchery without an iodine bath. The container used for the iodine bath should be equipped with an airstone or some type of agitator. Large differences in temperature should be avoided. To reduce temperature stress, mix equal parts of transport water and hatchery water for the initial iodine dip. As the iodine solution loses its color, it should be replaced. If large egg masses are to be divided, this should take place in the iodine bath.
Similarly aged egg masses should always be hatched together in the same trough. A newly laid egg mass should not be placed in the same trough as an advanced mass, unless no other space is available. This practice will save work in the long run and allow more frequent disinfection of hatching troughs. Large egg masses should not be folded or crowded into hatching baskets. If necessary, they should be broken into manageable pieces during the initial iodine dip.
Dissolved oxygen should remain at 5 mg/I in all hatching troughs. Hatching temperature should be maintained at 77°F (25°C) to 82 °F (28°C). Temperatures below this range encourage fungal outbreaks, while temperatures above this range encourage bacterial infections, developmental deformities and channel catfish virus in swim up tanks. Early in the season, water can be warmed using a hot water heater. If the water is too cool, development is slowed and too much hatchery space is tied up waiting for fry to come on feed.
Hatching water hardness should be at least 10 mg/L, and some authors recommended levels of 50 mg/L or above. Cooperative Extension Service county agents and fisheries specialists can assist in setting up a drip system to add hardness in the form of calcium chloride to hatchery water systems when required.
Check all egg masses at least twice daily. This involves inspection and removal of fungal or bacterial problems, shaking egg masses to remove any debris or sediment and turning egg masses over to ensure more uniform aeration during development. Egg masses can be routinely dipped in an iodine solution once (or even twice) daily until one to two days before hatching. This practice is especially beneficial late in the season if hatchery water cannot be maintained below 82 °F.
If there is too great a difference between the hatching time of the oldest and youngest spawns in a trough, the egg shell and protein debris from the early hatching spawns must be removed to avoid bacterial infection of fry and unhatched eggs. This means unnecessary work for hatchery personnel, so egg masses should always be grouped by similar age in hatching troughs. When pond water is used, it may be necessary to reserve several troughs specifically for hatching. These troughs can be cleaned more often or even provided with a recirculating water source to prevent buildup of pond sediments and fouling organisms.
Upon hatching, sac fry are usually siphoned out of the hatching trough. When siphoning sac fry, never let them pile up more than 2 or 3 inches deep in the containers they are collected and counted in.
Depending on its dimensions and water depth, up to 300,000 sac fry can be produced at a time in a hatching trough. Sac fry from one hatching trough can be placed together in one rearing trough for up to three days after they begin feeding. Usually, as fry begin to feed and grow, they must be split into additional rearing troughs or moved directly to fingerling ponds. Most hatcheries avoid this extra work and split the fry into two rearing troughs as they are removed from the hatching trough.
After hatching is complete in a trough, it should be drained, scrubbed, disinfected and rinsed well. Aerators, standpipes, screens and airstones should be cleaned with bleach, since these objects provide an ideal surface for bacteria. Siphon tubes, collection buckets, tubs and cylinders should all be disinfected with iodine solution, but avoid poisoning nearby troughs during the cleaning process. Good hygiene can greatly increase survival over the spawning season, and even small improvements in survival translate into thousands of pounds of harvestable fish.
The longer fry can stay in the hatchery without becoming too crowded, the better. If space is limiting, some fry can be moved out after they begin to feed, while others remain in the hatchery for five to seven days for added growth. These larger fry can be placed in a separate fingerling pond to provide an earlier source of fish for stocking. If it becomes necessary to move fry at an early age, it may be desirable to initially stock them into staked net pens, or “hapas,” for the first week in the fingerling pond. This will allow easier feeding and protection against any predators, until fry have gained some size. To keep track of numbers produced and stocked, it is a good practice to manage all the fry from one hatching trough as a unit.
A number of disease problems can affect hatchery success.
Fry Pond Management
Based on recent research at Mississippi State University, you can count on spending roughly $80 per water acre on fry pond preparation, including pumping costs, fertilizer and any required weed or predator control. The first step in preparing a pond for fry production is draining. Trash fish and any catfish fingerlings or stockers left from the previous year must be completely eliminated. In some instances, infestations of green sunfish or bullheads can cause high levels of mortality by preying on catfish fry. Yearling fingerlings and stockers can compete for food and reduce fry growth and survival.
If you’re sure trash fish and holdovers are not a problem, it is not necessary to dry the pond bottom completely. Keeping the pond bottom moist will help establish a good bloom when the pond is refilled, but, if large numbers of green sunfish have been in the pond, drying may be necessary to ensure any eggs do not hatch after the pond begins to fill back up.
Once they are filled, don’t let fingerling ponds sit too long before stocking them.
This will only allow time for predatory insects to become established. Ideally, fry should be stocked no more than two weeks after a pond has been filled, unless a bloom cannot be established or the well water being used is so high in iron or ammonia that more time is required for those substances to dissipate. Begin filling each fry pond no sooner than your pumping capacity requires.
As ponds are filling, fertilizer should be added to establish a good bloom. Liquid pond fertilizers such as 10-34-0 should be applied to the pond at 1 gallon per acre every other day for the first eight days or until a good bloom develops. Cottonseed meal, soybean meal or catfish feed should also be added at 20 pounds per acre each day untit the bloom visibility is 15-18 inches.
Get a bloom on fast, so fry can be stocked into an environment with lots of natural food, where predators have not had a chance to become established. Allowing fry to out-grow predatory insects is more profitable than trying to control those insects with oil slicks or chemicals. Never use unapproved insecticides in fry or fingerling ponds, since these fish are being raised for human consumption. If oil slicks are used, they should be applied sparingly (4- to 8-day intervals) and timed to minimize the possibility of poisoning fry during feeding.
If pond water remains clear, fry survival will be usually be low. For this reason, fertilizer is even more essential than feed during the first several weeks of management. Even so, fry should be fed at 20 pounds per acre per day with mini pellets or ground feed (mash). After fry begin feeding at the surface (usually within four weeks) feed them as much floating feed as they will eat in a 20-minute period, twice a day if possible. Smaller pellets and higher protein levels will increase growth rates and reduce size variation.
If fry are stocked at 50,000 to 70,000 fish per acre, they should be 5-8 inches long by the end of their first growing season. Even with good management, fry survival is highly variable from pond to pond, resulting in variable yields and sizes. For this reason, many fingerling producers overstock their ponds in relation to their production goals, sometimes by as much as 50 percent.