|Langston University Aquaculture|
Proactive Pond Management
George Luker Conrad Kleinholz
LOW PROCESSOR PRICES, in 1992 and 1993, increased the difficulty of profitable catfish farming. For many producers, production costs were greater than the price paid by the processors. To avoid selling at a loss, some catfish producers attempted to retail their crop or waited for prices to recover. Others decided that catfish farming was too risky and stopped production.
In the southern U.S., many catfish farms are managed to maximize production with high stocking (5 - 10 thousand/acre) and feeding (75 - 150 pounds/acre/day) rates. Typically, seasonal feeding rates are increased on these farms until mechanical aeration is necessary. Often, therapeutants are required to manage the disease and parasite problems which accompany or follow these poor water quality periods.
For the past five years, annual catfish projects at Langston University were designed to evaluate bighead carp polyculture as a means to improve catfish production and pond water quality. Annual project ponds were stocked at 3000 - 3600 catfish/acre and produced 3000 - 4200 pounds/acre. Project lengths (stocking to harvest) ranged from 160 - 220 days (April - October). Annual catfish feed conversion ratios (FCR) ranged from 1.069 - 1.290 with an average of 1.148. Annual catfish survival ranged from 95.17 - 98.76 % with an average survival of 96.95%. Catfish production, FCR and survival were not affected by the presence of bighead carp. These results were obtained without the use of mechanical aeration or therapeutants.
A proactive pond management method based on catfish production and water quality analyses has resulted from these projects. Proactive pond management seeks to provide additional profits by reducing production overhead, rather than by maximizing production. Profits are gained through improved feed conversion, catfish survival and water quality. As the term proactive implies, this management method attempts to prevent catastrophic pond events from reaching lethal intensity.
Important steps for implementing proactive management follow.
1) Grade your fingerlings. Using graded 7 - 8 inch fingerlings (75 - 130 pounds per thousand), in annual production systems, helps to ensure improved feed conversion and fewer under sized fish at harvest. Small fingerlings have difficulty competing with large fingerlings for food throughout the growing season. Despite the higher initial cost for larger fingerlings, they are more cost effective than smaller fingerlings.
Previous research at Langston investigated the influence of fingerling size on production of caged catfish. Fewer harvest size fish (40%) were produced from mixed size fingerling classes (8, 6, and 4 inch) than from single size 8 inch (93%) or 6 inch (49%) fingerling classes.
2) Stock 3000 - 3600 catfish per acre. This is the stocking range we have used successfully. Higher stocking rates may be possible with this management method but are unproven at this time.
3) Stock fathead minnows (10 pounds per acre). Bighead polyculture did not directly affect catfish production in the Langston experiments. However, plankton populations and water quality parameters were more stable in the bighead ponds. Fathead minnows should provide polyculture benefits similar to those from bighead carp. Fatheads feed on periphyton, zooplankton, insects, waste feed and detritus. This behavior will help to moderate plankton blooms and organic waste loading. Fatheads can also provide additional food for catfish and extra farm income, if bait markets are established. Four, hardwood loading pallets per acre will provide adequate spawning structures for the fatheads.
4) Use high quality feed. Using a nutritionally complete, 36% protein, floating ration is an important component in proactive pond management. Feed must provide complete nutrition with maximum conversion efficiency. Extra protein is needed to ensure rapid growth without reducing water quality. Lower quality feeds often have poorer conversion efficiency, which results in more waste products.
5) Use reduced feeding rates. Many commercial catfish producers feed to satiation (all the feed the fish will eat) daily or use a feeding schedule based on estimated fish weight (3 - 5% of fish body weight per day). This feed rate amounts to 75 - 150 pounds/acre/day through much of the peak growing season. Heavy reliance on mechanical aeration often follows the obligatory water quality problems associated with this traditional management method. Mortality from diseases such as Enteric Septicemia of Catfish (ESC) also increases dramatically at high feeding rates. These problems combined with higher feed conversion rates result in reduced profit potential for many growers.
In the Langston experiments, feed rates began at 0.5% of stocking body weight. Feed input increased gradually as the water warmed and when the fish ate the feed within 5 - 10 minutes. Feed rates, during the peak growing season, ranged from 20 - 40 pounds/acre/feed day. This feed rate produced market size catfish (1.0 - 1.25 pound average) in 180 - 220 days without aeration or disease problems. The proportion of sub-harvest size fish (< 0.75 pounds) ranged from 5 - 15 % of fish harvested. Accurate, daily records of feeding rates for each pond are very important for successful pond management.
Some farmers accustomed to feeding to satiation or feeding from a schedule based on estimated body weight, may find it difficult to reduce feed inputs. The goal of the Langston experiments was to provide at least one pound of feed for every fish stocked. For example, a one acre pond stocked with 3600 fish was to receive 3800 - 4000 pounds of feed (3600 pound minimum) during the growing season, water quality and weather conditions permitting. Our experiences with commercial farms indicate that two or more pounds of feed per fish results in reduced feed conversion and associated water quality and disease problems.
6) Spread feed evenly. It is very important to scatter feed over as much of the pond as possible when using reduced feeding rates. Otherwise, aggressive, larger fish will "hog" the feed and reduce feed efficiency. If your feed application system is limited to a small area of the pond, divide the feed into two or more feeding passes. Catfish will learn your feeding patterns, so occasionally reverse or alter your pattern, to provide an opportunity for all fish to obtain feed.
7) Avoid overfeeding. Feed input is the primary pond control mechanism a catfish producer has once the pond is stocked. Catfish need adequate food for growth and health. However, fat, overfed catfish are not more healthy than catfish fed in efficiently managed systems. In most ponds with ESC outbreaks, the largest fish are infected initially.
At what feeding rate does overfeeding begin? Uneaten feed collecting on the pond edge is a sure sign of overfeeding. Also, even if all the feed is eaten promptly, the fish may be overfed. When consumed feed isn't efficiently converted into tissue, the fish are overfed.
Waste products from catfish which are efficiently converting feed to tissue will enrich the pond with nutrients, resulting in plankton blooms. Food conversion efficiency in catfish goes down when they eat more than necessary for optimal growth. When the catfish are overfed, these additional waste products stimulate the development of large, unmanageable plankton populations. Nutrient and/or oxygen requirements of one or more of the populations may exceed the supply rate, resulting in a crash. Nutrient concentrations may reach toxic levels before these populations can recover. Aeration and therapeutants may be required to limit the onset of fish disease or mortality.
The Langston experiments required that each pond receive the same quantity of feed for each feeding day. On many feeding days, some ponds could have been fed at higher rates. At other times, some ponds could have been fed when feeding was curtailed. Our projects received only 20 - 40 pounds of feed/acre/day, (acre and quarter acre ponds), through most of the growing season. Feeding more than 40 pounds per acre may be possible in your ponds while maintaining excellent conversion efficiency. It is very unlikely that all your ponds can be fed at the same maximum rate. The most reliable way to determine your maximum feeding rate is to monitor water quality for each pond.
8) Monitor water quality. Daily dissolved oxygen (DO) and temperature, and regular (weekly or bi-weekly) alkalinity, pH, total ammonia nitrogen (TAN), and nitrite-nitrogen measurements are critical to develop a production profile for each pond. This water chemistry profile coupled with daily and extended weather forecasts can help you avoid or lessen the effects of critical water quality problems, and, improve profit potential through increased feed conversion efficiency and reduced aeration expenses. Water quality test kits, which can perform these tests for fish farmers, cost approximately $175 - $200. Time requirements for daily DO measurements will average 10 - 15 minutes/pond/day.
9) Clean your ponds. Organic debris accumulates on pond bottoms as a result of any catfish production. Drying and stirring this debris helps to oxidize organic wastes and may help curtail chronic disease problems. Seining efficiency should improve also when the pond bottom is reflattened. Make sure to repack the pond bottom before refilling. Wastewater guidelines prohibit discharge of pond bottom sludge to streams. Pond bottom sludge may be applied to fields or gardens as long as it cannot contaminate streams.
10) Lime your ponds. After cleaning, adding ag lime can improve the production potential of most ponds by increasing their buffering capacity. In ponds with total alkalinity of 60 mg/l or less, 1 - 2 tons per acre are recommended. For ponds with total alkalinity of 60 - 100 mg/l, 1 ton per acre is sufficient. If a pond leaks badly, liming isn't cost effective. As you record and maintain information on your ponds, you can determine the quantity and frequency of liming required for each pond. Ag lime may be purchased from most agri-chemical dealers or from highway construction companies.
What to Observe
1) Average early morning (6 - 8 A.M.) DO concentrations will decline slowly through the spring to summer period, even though the day to day concentrations may fluctuate. During this period, morning pond temperatures and your feeding rate will slowly increase. Once pond temperatures begin to stabilize, trends in DO concentrations become very important. When morning DO decreases consistently for 3 - 5 days (3.0, 2.3, 1.8 mg/l, for example) consider this a significant trend and reduce feed input. When the morning DO concentration returns to pre-decline levels, increase feed input by 10%/day to original levels. Skip feeding on days when morning DO is less than 1.8 mg/l.
A rapid increase in morning DO concentrations, when weather conditions are stable, indicates that an algal bloom has begun. Increasing feed inputs during these periods will usually result in a serious water quality event if the bloom crashes.
A weather forecast predicting cloudy (overcast), cool or stormy weather can be expected to result in declining DO in many ponds, especially those with dense algal blooms. Reducing feeding rates as a weather front approaches can soften the impact on DO, and, nutrient concentrations and plankton populations. Despite the reduced feed inputs, plankton populations can still crash if you push the pond limits during poor weather conditions. Your ponds should recover within a day or two if you have not been overfeeding. Be sure to measure DO and TAN frequently during these difficult periods. Keep a record of these measurements for future reference.
Proactive pond management helps to prevent reliance on mechanical aerators. The ponds used in the Langston experiments do not have aeration capability. If your pond develops a DO problem, use your aerator. As soon as weather or pond conditions improve, stop aerating and allow the pond to recover normally.
2) Abrupt changes in pH and alkalinity usually indicate major changes have, or, are occurring in the pond phytoplankton (algae) populations. As algal population carbon requirements exceed available carbon dioxide levels, algae will use carbon from the pond buffer supply and alkalinity will decline. Reduce feeding for a few days to allow algal populations and alkalinity time to stabilize. Heavy rains can also cause alkalinity to decline. In either case, alkalinity should stabilize at or near previous levels; if not, add ag lime as needed.
3) As feeding rates and pond temperatures increase, TAN and nitrite-nitrogen levels will increase. When you reach the target feeding rate (25 - 40 pounds/acre/day), TAN and nitrite-nitrogen levels should stabilize near 0.4 - 1.0 mg/l and 0.002 - 0.3 mg/l, respectively. However, ponds which are highly enriched from years of accelerated production may have nutrient levels outside, usually above, these ranges. At this point, changes in nutrient concentration indicate changes in algal or bacterial populations if weather conditions are stable. Algae use ammonia readily when sunlight is available. If feed rates are constant, an increase in TAN concentration usually means that algal populations are declining. Weather changes that affect DO concentration, will affect TAN concentration also, because algae are the primary DO contributors/users and TAN users.
Measurements of algal density (chlorophyll-a concentration) and chemical oxygen demand provide very useful information to our project, but are expensive and complicated. We are continuing efforts to find other accurate estimators for these parameters that are more suited to commercial growers.
4) The catfish ponds used in this research had common levees, common water source, identical stocking and feeding rates. However, some ponds reacted differently to environmental and management stimuli. Important decisions, based on analyses from your ponds, may occur at DO or TAN concentrations other than those we found. Record the information gathered from each of your ponds to increase your effectiveness.
Individuals or groups interested in observing, our water sampling and analyses are invited to visit our facility.
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