Successful fish culture, whether it is done in cages, open ponds, or in some other manner, is more than just harvesting a few fish at the end of the growing season. Having a successful and profitable harvest requires that the producer understand the variables that influence success.
This publication focuses on harvesting, a “post-production” activity, and economics, which determines how production can be improved. Attention to detail, good record keeping, and an understanding of how various input costs affect the bottom line will help the producer analyze the overall operation and formulate a plan for next year.
Harvesting:
The ease of harvesting caged fish is one of the reasons people choose cage culture. Basically, all that is required is a dip net to capture the fish and containers in which to place the fish until they can be sold or processed.
Harvesting can begin when a significant portion of the fish reach a size the market is willing to accept. As a rule, the value of fish per pound does not increase once they have reached the minimum market size.
Although the size of the individual fish and the total pounds of fish in the cage should be increasing over time (assuming that growing conditions are favorable), risk exposure continues as long as the fish are in the water.
The culture of fish, like any crop or commodity, carries risk that must be kept to an acceptable level. Therefore, it is advisable to harvest fish as soon as is practical after they reach a marketable size. The culture period—the time between stocking and harvest—is quite variable and depends upon factors such as species, size and density of fingerlings stocked, time of year stocked, climate and weather.
Overall culture conditions such as water quality, disease incidence, and other possible stressors also affect the length of the culture period. When warm-water fish such as catfish are cultured in the warmer parts of the southern region, fish stocked in the spring often can be harvested in the fall or winter of the first growing season, assuming that they have grown large enough.
In cooler areas fish may have to be overwintered and finished the second or even the third season because there are fewer optimal temperature days per growing season when higher feeding rates are possible. Although overwintering fish may extend the period that the producer can offer fish to his customers, the unnecessary holding of marketable fish is risky at best.
The culture of what might be called “non-temperate climate” fish requires different production strategies and harvest seasons. For example, in the warmer parts of the southern region, the stocking of rainbow trout and other cold-water species usually occurs in the fall, with grow-out during the cooler months. These species’ poor tolerance of warm water means that they must then be harvested before water temperatures rise above 65 to 70 °F (18 to 21 °C) in the spring.
Because the fish must reach market size quickly, culturing them is difficult in all but the more northern or higher elevation parts of the region. The culture of tilapia, which require consistent water temperatures above 60 °F (15 °C), is challenging in all but the most southerly parts of the country. Such climate challenges give the producer added incentive to produce fish quickly, but limit the culture of both trout and tilapia.
No matter how carefully fingerlings are graded before stocking, the fish will not all reach market size at the same time. Differences in growth rate are caused by a variety of factors, including genetics and social structure. Some fish may simply grow faster in the production culture conditions and, therefore, have a genetic advantage.
Some may dominate the feeding area and get more of the available feed. In any case, it may be possible to do a partial harvest by removing only the fish that have reached market size. However, this can cause considerable stress for fish, especially if done while water temperatures and, thus, the metabolic rates of the fish are high.
Physical injuries caused by fish-to-fish and fish-to-equipment contact can lead to disease. After a partial harvest, fish density in cages is lower, which may lead to aggressive behaviors and injuries.
Before harvesting, it is important to test a few of the fish for off-flavor. If the fish taste muddy, musty, oily, or have any strange flavor, they should not be harvested. While off-flavor is most common during the warmer months when water conditions are most stable, it can occur at any time of year. Off-flavor can be very persistent, lasting from a few days to several months.
Fish that exhibit off-flavor in the fall when water temperatures cool may still have off-flavor in the spring. Some consider off-flavor to be the most serious challenge in the catfish industry; it causes greater financial losses than diseases because it delays harvest.
Buyers, especially first-time consumers, will be reluctant to purchase fish again if their first experience was unpleasant. The producer should stop feeding the fish at least 2 days before harvest in warm weather and up to a week before harvest in cool weather.
This gives the fish time to empty their digestive systems and it reduces hauling, holding and processing problems. Excessive waste fouls the water in hauling and holding tanks and may stress the fish sufficiently to cause disease or death. Although fish destined for a processor will not have enough time to develop a disease, fish being sold to a live market or fish-out may.
Fish that are dead on- arrival (at the processor or fish out) or that die soon after delivery (at a fish-out) can cost the producer considerable money and possibly future sales.
Food in the gut of fish reaching the processing plant means the processor has paid for unmarketable weight. At harvest, the producer should record the number of fish harvested and their total weight (length records could also be useful).
These records are necessary for analyzing an operation and improving its efficiency. A financial analysis should include a profit and loss statement and the cost of production per unit (a pound of fish).
The cost of producing a pound of fish is calculated by adding all input costs (accounts payable) and dividing the sum by the units (pounds of fish) marketed. Do not forget to include your labor as an input, as it certainly has value, too!
Author:
Peter Woods and Michael P. Masser
