Larry W. Dorman
Introduction
Hatching channel catfish eggs in spawning jars is nothing new. Researchers attempted this as early as the 1950's. Whole spawns were placed in spawning jars and water was circulated through the jars. Problems due to fungal infection and poor oxygen circulation to the individual egg doomed this method.
Years later, researchers improved this technique by separating the spawn into individual eggs. This method involved dissolving the matrix tissue (tissue which holds the spawn together) with a 1.5 percent sodium sulfite (Na2 SO3) solution. This allowed better circulation to the individual egg and thus improved hatchability.
This method of hatching catfish could be utilized by Arkansas fish producers without the addition of elaborate new equipment
Food and Drug Administration's Policy
For many years sodium sulfite was classified by the FDA as a Generally Recognized As Safe (GRAS) compound. The compound could legally be used to treat the eggs of several fish species. Due to a recent change in the FDA regulatory policy, many compounds are now undergoing re-evaluation. Also, the GRAS classification has been eliminated.
Recently, the FDA ruled that sodium sulfite (along with 4 other compounds) is a new animal drug of low regulatory priority. Sodium sulfite can be used as a 15 percent solution for five to eight minutes to treat eggs of catfish, largemouth bass, and smallmouth bass to improve their hatchability.
Procedures for Dissolving The Matrix Tissue with Sodium Sulfite
1. Make a 10X concentrated stock solution. Dissolve 150 grams of sodium sulfite (Na2 SO3) per liter of distilled water. Store this in a large plastic container until needed.
2. Take 100 milliliters (ml) of the stock solution and add 900 ml of hatchery water. This is the 1.5 percent solution needed.
3. Adjust the pH of the solution to that of the hatchery water. The sodium sulfite solution should be slightly basic. Ground water in the Arkansas Delta is usually slightly basic so little adjustment may be needed. However, for neutral or slightly acidic hatchery water, add 10 percent hydrochloric acid (HCl) to the stock solution until the pHs are the same.
4. Place the spawn in a plastic pan or stainless bowl and cover with the sodium sulfite solution.
5. Gently stir five to seven minutes with a glass rod until the eggs are separated.
6. Decant the solution and thoroughly rinse the eggs. This eliminates the matrix tissue and any dead eggs. This step is critical; the degree of fungal infection depends on the quality of rinsing.
7. When rinsing is completed, drain the water. Pour the eggs in a 1,000 ml graduated container. Determine the total volume of eggs. To determine the number of eggs, count the number of eggs in a 5 ml sample, and apply that number to the total volume of eggs. For example if there were 125 eggs in the 5 ml sample, then 1,000 ml would contain 25,000 eggs.
8. Pour an estimated 40,000 eggs per spawning jar. Set the water flow at 2 to 3 liters per minute or enough flow to gently stir the eggs (enough flow to suspend the eggs).
The eggs from a fresh spawn should hatch in six to ten days depending on the water temperature. The preferred water temperature is 78 to 80 degrees Fahrenheit. Once hatching is completed, move the sac fry to circular tanks, rearing troughs or other such facilities until the fry are large enough to stock in a pond.
Comparison to Traditional Hatching Methods
If you use the traditional spawning methods for hatching catfish, do not drop those and implement these methods. However, in several cases, the spawning jar method has some advantages. These advantages include:
1. If spawning other species such as Chinese carps, striped bass or hybrid striped bass, no new equipment is needed to include catfish.
2. Less space is needed for hatching jars as opposed to hatching troughs.
3. Less expensive to use this method in some cases. Three liter soft drink bottles can be used very satisfactory in the place of expensive spawning troughs or McDonald hatching jars.
4. Less electricity is needed since no motor driven paddles are needed for agitation.
5. There is less chance for disease infection on the eggs since the matrix tissue is removed.
Conclusion
The spawning jar method offers some advantages over traditional means of hatching catfish. This method can allow existing hatcheries to include catfish in their production without the addition of expensive equipment.
LARRY W. DORMAN is Extension fisheries specialist, University of Arkansas Cooperative Extension Service, Pine Bluff.
FSA9071-2M-1-93-S421
Issued in furtherance of Extension work, Act of September 29, 1977, in cooperation with the U.S. Department of Agriculture, Dr. Mazo Price, Director, Cooperative Extension Program, University of Arkansas at Pine Bluff. The Arkansas Cooperative Extension Program offers its programs to all eligible persons regardless of race, color, national origin, sex, age, or disability, and is an Equal Opportunity Employer.