Hatchery and Brood Fish Management

Many strides have been made in the catfish industry during the last several decades. The industry has progressed from the days of collecting brood fish from local streams and rivers, placing those fish in brood ponds or pens and allowing the fish to spawn, to the recent development of selected lines of fish with improved growth and disease resistance.

Even with the genetic improvements in brood stock, spawning success is often quite low. On average, only 50 percent of females actually spawn. Additionally, survival from the egg to fingerling stages, estimated at 60 percent to 70 percent, could use some improvement.

In some instances, poor spawning and survival is attributed to natural causes or causes beyond the fish culturists’ control. In other cases, poor brood performance and lack of fry survival are caused by errors made by the fish culturist, such as poor timing for certain activities or poor cultural practices. Improvements in facility design and operation may improve spawning success and survival.

This article reviews spawning, hatchery and culture practices used on farms and makes suggestions for improvements.

Evaluate Your Brood Fish — The first step to improvement begins with evaluating your brood fish. The hatchery manager should evaluate brood fish performance and make goals for improvement. Records of performance are important. How did the brood fish perform the previous season? Several numbers are needed - the total number and weight of brood fish, the weight and number of female brood fish and the number of spawns attained. Also needed is an estimate of the number of eggs per spawn.

Evaluate these numbers and determine the number of eggs produced per pound of female brood fish. If the number is less than 2,500 eggs per pound of female brood fish, look for a new line of brood fish. A good line of brood fish produces more than 3,000 eggs per pound of female.

Consider fry and fingerling performance. At reasonable stocking rates, ranging from 100,000 to 200,000 fry per acre, how fast do the fingerlings grow? Are the fingerlings still three inches or less in length in November? or larger? Replace a slow growing strain. Also, note the number of females that actually spawn. If this number has been less than 40 percent the past two years, then replacement brood stock are needed.

Keep careful track of the age of brood fish. Three to four year old fish in the 3 pound to 6 pound size range usually perform well. They produce large numbers of eggs in relationship to body weight, and a high percentage of females spawn. Also, fish of 3 to 6 pounds are in an ideal size range for the spawning receptacles made from old ammunition propellant cans, which are used on most farms. Fish larger than 8 pounds will not spawn in these containers because they cannot fit comfortably inside them.

Examine and cull brood fish each year. Late fall through mid-winter is a good time for this activity. Fish handled too near the start of spawning season may be stressed and may not successfully spawn, so don’t delay.

Brood fish are seined and crowded and individually examined. Select fish with good traits — body shape, size and robustness. Discard fish with any deformity or undesirable trait. Set sex ratios at this time and stock fish in fresh brood ponds at 3 to 1 female to male or 3 to 2 female to male. Brood fish should never exceed 1,200 pounds per acre.

Feed brood fish a 36 percent crude protein pellet at 2 percent body weight daily when water temperature is above 70ºF. When water temperature is between 55ºF and 70ºF, feed fish 1 percent body weight three days per week. When water temperature is below 55ºF, don’t feed.

Locating Improved Brood Fish Lines — Many private hatcheries have developed excellent lines of brood fish by selecting fish with the most desirable traits and especially improved growth rate. These hatcheries are the most readily available source of brood fish for the industry at present. These brood fish are of known age and are reasonably priced.

A genetically improved line of catfish, the USDA/NWAW 103 strain, has been available to catfish producers for the past three years. Some private companies also offer genetically improved lines. These are excellent brood fish. They offer faster growth and improved disease resistance. They generally spawn at three years of age and produce very high numbers of eggs relative to body weight. Because individual egg size is smaller than standard farm strains of catfish, the number of eggs per spawn is higher.

Price is a major drawback to the genetically improved fish; however, with the current industry downturn, the 103 fingerlings are not bringing a premium price. Another drawback is that the brood fish may be sold at a size too small to spawn so they must be grown a year before serving as reliable brooders.

Furthermore, farm facilities are evaluated before releasing improved strains to farms. Researchers who developed these lines require as much isolation of these fish as possible to maintain genetic integrity. Not all farms that want these fish qualify to receive them.

Practices to Avoid — Know the age of fish you purchase. The largest fish from a food fish farm are not always the best brood. Fish from food fish farms may be large simply because they have successfully avoided being seined in past years, and nobody wants fish which are wise enough to avoid the seine or with slow growth. Some farms place brood containers in food fish ponds and collect eggs. This is common when fingerlings are in very short supply, but it is not a good strategy because fry are not selected for optimum traits.

Hatchery Considerations — Hatcheries vary considerably in design, from elaborate facilities with specialized equipment to low cost portable tanks placed in the corner of a farm shop. Regardless of design, water quality and quantity is the major consideration. Hatching tanks require a minimum of 2 to 5 gallons per minute. Most hatcheries with newer wells meet this requirement. Beware of slow water flow from corroded screens on older wells.

Check water flow at hatcheries during winter. Open valves or spigots into each trough and use a stopwatch as you catch water in a graduated container. If water flow is less than 2 gallons per minute, improvements are needed. Some situations require an alternate water source, or replacement of well screens or other parts. Some producers pour concentrated hydrochloric acid into wellheads to dissolve minerals on the screen so the water flow can return to full capacity.

Other water quality considerations are listed in Table 1.

Special Problems — Water temperature is another important consideration. Many hatcheries use groundwater from shallow aquifers. Water from this particular aquifer is usually in the mid-60’s. Ideal temperatures for hatching range from 78 - 80ºF. For every two degrees above or below 78ºF, add or subtract a day from the hatching time. If the water temperature is below 75ºF, then the spawns are susceptible to fungal infections. If the water temperature is above 85ºF, the spawns are susceptible to bacterial infections, and the fry may have genetic deformities. Table 2, gives the stages of channel catfish egg development at 78ºF.

Table 1. Desirable water quality values associated with hatching channel catfish eggs.

Parameter Measured	Desirable Range
Dissolved oxygen	5 ppm to saturation
Carbon dioxide	less than 15 ppm
Total alkalinity	50 to 400 ppm
Total hardness	50 to 400 ppm
Calcium hardness	10 to 160 ppm
pH	6.5 to 9.0
Iron	less than 0.5 ppm
Hydrogen sulfide	0.000 ppm
Temperature	75ºF minimum

Table 2. Stages of channel catfish egg development at 78ºF.

Distinctive Feature	Age(days)
No internal pulsation (heart beat)	1
Pulsation visible	2
Bloody streaks visible	3
Entire egg bloody in appearance	4
Eyes visible	5
Eyes prominent, embryo turns in shell	6
Embryo complete, no bloody streaks	7
Hatching begins	8

Another problem encountered on heating water is gas supersaturation, particularly problems with nitrogen gas. Fry develop gas bubbles beneath the skin and in severe situations massive mortalities can occur. To remedy this situation, the water must be aerated before being heated. Aeration strips the gas from the water and prevents the problem. Pump water from the well into a vat or trough with several air stones running, and then pump it into the water heater.

High iron can also be a problem in water from the shallow aquifer. Iron filtration is needed if 1to 6 ppm are reported. Iron filtration involves aerating the water and letting the iron settle out in a holding vat. Pump the water through a series of filters to remove the remaining iron. These filtration systems may be as simple as a series of swimming pool filters linked together to very complex type systems with automatic backwash settings. Once the iron is removed, the water is ready to be heated and pumped into the hatchery.

This article is not intended to solve all problems that a fish culturist may encounter but to stimulate thought, through solving problems.

By Larry Dorman, Extension Fisheries Specialist
Arkansas Aquafarming newsletter (Volume 20 No. 1)
University of Arkansas Cooperative Extension Program