What are the causes of mortality? Is all mortality in catfishes natural? This and many other questions are often asked by catfish farmers, most especially new farmers who are willing to minimize loss due to mortality. Times without number, catfish farmers have been sent out of business due to uncontrolled mortality rates. Some six years ago, I was seriously affected by severe mortality in my catfish farm. I almost lost my confidence in the business. I began to search for basic causes of mortality in catfishes and how to control mortality if there is any solution to this problem. In this article, I shall be examining various causes of catfish mortality. This I believe will make farmers to reduce the effect of mortality once the cause is known. For easy reading, causes of catfish mortality have been grouped into five categories. Each category will be discussed briefly to give sufficient information on this matter.
Causes of Catfish Mortality
1. Feed induced mortality
Mortalities in this category are caused as a result of overfeeding, contaminated floating feed, and high level of Aflatoxin in certain feed ingredients used in feed formulation, leading to feed poisoning.
- Overfeeding: It is one of the major causes of high rate of mortality in fingerlings and juveniles. Just like little kids, juveniles have uncontrolled appetite to feed, they sometimes overfeed and die. In such a situation a farmer only needs to reduce the feed intake in other to reduce or stop the rate of mortality completely.
- Contaminated floating feed: Experience has taught me that sometimes manufacturers of feed (floating feed) make mistakes. Especially in an attempt to reduce cost of production, some manufacturers make use of certain ingredients with high level of Aflatoxin above acceptable limits. Farmers at the short run usually pay dearly for the errors committed by their feed producer. Although some of these products are out of market, which means these companies also go out of business in the long run.
My experience in this regards was not a pleasant one. Around 2011 or thereabout, a once popular indigenous floating feed manufacturer supplied some tons of feed to the farm where I worked. As we fed our fishes with those feeds, about 100 mortalities were recorded per day for almost 2 weeks. Many drugs were administered, but as soon as feeding resumed mortality rate continued until we discovered high level of toxins through test. Then we stopped feeding and returned the remaining stock of feed to the producer. Although we were compensated, but the loss incurred was not commensurate with the compensation given. Recently, the same problem was discovered in feed produced by another indigenous company. I am not an advocate of imported fish feed but the indigenous companies need to improve in the area of quality control before and after production.
Another cause of mortality closely related to contaminated feed is expired feed sold in the market by certain dubious retailers. These expired feeds are capable of causing high mortality rate in catfish and farmers may not really notice the expiry date because it will have been changed by these retailers.
- Aflatoxin: This is a form of poisonous chemical substance produced by a fungus which resides in soil and decaying dead organism in farm or storage. According to certain research, aflatoxin contaminates up to 25 percent of maize and groundnut produced in the country. Aflatoxin easily contaminates maize and other grains that are not properly dried before being stocked or when drying process is delayed. It is unavoidable but must not be too high in feed. Grains such as maize, millet, sorghum, etc.; legumes such as soy beans, cowpea, etc.; and nuts such as groundnut; and host of other feed ingredients can be contaminated by aflatoxin. Due to poor control of livestock feed in Nigeria, some feed millers use these feed ingredients without appropriate tests to determine the level of aflatoxin in such feed. These feeds containing above normal level of aflatoxin are passed to poor farmers to feed their catfishes. For catfish farmers who care to know, aflatoxin-contaminated ingredients can be identified through:
– Laboratory tests
-Careful observation (any ingredient that look moldy)
– Color observation (discolored ingredients)
Effects of aflatoxin on catfishes, especially young fishes, are endless. They include liver damage, liver cancer, stunted growth, weakened immune system, poor feed efficiency and high level of mortality to mention a few. Farmers should be watchful to reduce avoidable mortalities through the use of uncontaminated feed ingredients. Once mortality due to aflatoxin is discovered, farmers should stop the use of such feed and mortality will stop. Farmers can also constitute the habit of using toxin binders in case of any doubt.
- Mortality due to deficiency in feed ingredient: Mortality may occur as a result of poor feed formulation, especially when certain vital nutrients are absent in the feed. There are certain important amino acids that must be present in catfish feed. If such cannot be found, catfishes are open to external infection as a result of lack of these important micro feed ingredients. From experience, it has been observed that “cracked head” in catfish is a feed deficiency disease. This disease alone can increase catfish mortality severally and also reduce economic value of few surviving ones.
2. Disease Induced Mortality
Mortality in this category is caused by infections. The effect of these infections can be severe if other conditions like feed, water, and environmental factors support the spread of pathogens causing the disease. In essence, diseases in catfish will be enhanced or suppressed by feed, water, stress level and other environmental conditions.
Catfish disease can be classified into internal and external and can be caused by bacteria, parasites, fungus, and worms.
– Internal disease: Ulcers (affects internal organs), Wormy disease (affect catfish appetite), Trichodina diseases (make fishes to swim on the surface).
– External disease: Skin cancer, white spots, cracked head, and ulcer.
Catfish diseases can be cured by salt solution, drugs, and Formaldehyde (formalin) solution depending on the type of infection.
3. Pollution Induced Mortality
Water is said to be polluted when the amount of impurity in such water body increases significantly to affect the wellbeing of aquatic animals. Catfish ponds can be polluted by several pollutants including waste feed. When there is notable increase in the level of pond pollution, fishes begin to die. As a matter of fact, water pollution is the number one cause of fish mortality. This is due to the fact that polluted water can encourage the growth of certain pathogens causing diseases and also expose immune ones to sometimes unbearable stress. Sources of pond pollution have been grouped into four for the purpose of this write-up:
- Pollution from feed waste: There is no way a catfish farmer can be so careful without losing some feed (sinking feed) as waste. At times, this waste could be due to overfeeding or poor feed production. Wastes are capable of increasing the level of ammonia and carbon dioxide in the water, although earthen ponds have the capacity to regenerate the water quality if the waste is not continuous. However, concrete ponds and other catfish production tanks cannot in anyway purify themselves. Hence, water must be changed constantly and regularly to reduce pollution induced mortality in these containers.
- Pollution from flood: Often times, storm water may find its way into catfish ponds when rain is overwhelming or as a result of careless handling of pipe networks (inlet and outlet pipes). This is not applicable to concrete tanks and other catfish production tanks.
Flood water is capable of depositing into the pond some sand and clay. Clay increases water turbidity which may lead to breathing difficulties for tilapias and catfishes. Apart from direct flood entering the pond, direct rainfall is capable of eroding dikes to increase water turbidity. The surroundings of dike can be grassed to reduce dike erosions. Nitrates, pesticides, herbicides, water plants (algae), etc can also be introduced into the pond through flood. Water plants introduced into the pond through flood can spread rapidly and increase the level of water pollution.
- Pollution from toxins: The use of smaller water bodies like stream as a source of water supply to our ponds could be very dangerous especially when the source of these water bodies is not known. Sometimes, these streams supply some ponds upstream and the polluted water from these ponds is drained into the same stream and reused downstream. Some farmers are fond of using toxin tablets to kill remnant fishes after harvest. This same water could be drained into nearby streams with toxin levels of such water still very high. Unknown to poor farmer downstream, same water is allowed into his ponds resulting in mass mortality without cure. Except such water is changed with fresh, unpolluted water, fish mortality continues. Direct poisoning of ponds can also occur in a non-friendly environment. That is why farmers should be as friendly/cooperative as possible with the host community.
4. Nature Induced Mortality
There is no way natural death will not occur. At times, some fishes will die naturally. It will not be a serious issue when there are two to three mortalities monthly in a 10,000 capacity fish farm. Farmers should ignore this. It only becomes a concern when the number of mortality increases above this rate.
5. Other Causes of Mortality:
i) Stress induced mortality: Stress is a state of unease in living organisms due to disturbance. There are many types of stress that can cause mortalities in catfish:
– Digestive Stress: This occur when catfishes are incubating or just recovering from disease. From experience, the best way to feed infected/recovering catfishes is to reduce their feed intake by at least sixty percent and to increase it gradually as they recover.
– Transfer Stress: This happens when fishes are transferred from one location to another, causing them to experience transportation stress. Any attempt to feed fishes under this type of stress will result in high level of mortality, so if you just stocked your fishes, hold on for at least twenty four hours before feeding them.
– Weather stress: This type of stress is related to harsh weather or drastic change in atmospheric condition. This change may include sharp drop in temperature, change in rain pattern, acid rain, etc. Change in weather takes catfishes a few days to adjust to, and during the period some of them might die.
– Harvest stress: It is not uncommon for farmers to complain of mortality during harvest. Some fishes that are healthy drop dead immediately after harvest or sometimes when harvested fishes are returned into the pond. The level of harvest stress causing mortality depends on how hardened the species of fishes stocked are. However, mortality due to harvest stress can be reduced when feed is stopped at least two days before harvest.
ii) Poor pond preparation induced mortality: My negative experience in this regards taught me a lot of lessons. I once left some hundreds of tilapia fishes in my pond before I stocked some juveniles. After some time, I started counting about thirty mortalities daily. I stopped feeding and I was about to apply some medication when I observed the cause of this high rate of mortality. I discovered that the dead fishes were the ones who attempt to swallow the tilapia fishes in the pond. They died as a result of the effect of tilapia bones in their throats.