Fish farming.
Nigeria is one of the largest producers of fish in Africa, accounting for about 10 percent of the continent’s total fish production. With several challenges such as lack of modern technology and insufficient finance opportunities, the country fish industry had being faced with a lot of set backs.
Protein is a major food nutrient for human and animals especially the young ones to develop and build their body tissues. Animal protein sourced from meat, egg, and milk cannot meat the need and taste of the human populace. Therefore, alternative protein source is needed to meet their need and change their taste. This can be achieved through fish consumption.
In time past, fishermen only source for fishes in natural water bodies which are sold to consumers. But as the world population increases, global demand for dietary fish protein also increased. Over exploitation of the natural water bodies for sea food resulted in drastic decrease in the aquatic animals. Therefore, people began to raise fish and other aquatic animals in artificial ponds to meet the need of the world.
Fish farming or pisiculture is a type of aquaculture which involves commercial breeding and rearing of fish, most often for food, in enclosures like fish tanks or artificial enclosures such as fish ponds. Aquaculture, is the cultivation and harvesting of aquatic animals such as fish, crustaceans, molluscs etc. For commercial purposes, juvenile fishes hatched from fish eggs in fish hatchery. Worldwide, the most important fish species produced in fish farming are carp,tunas, cod, catfish, salmon and tilapia.
The artificial fish colonies in ponds should be provided with sufficient feeds, protection from natural predators and competitive threats, access to veterinarian service, medication and easier harvesting.
Fish are farmed for human consumption (food), for fish oil, and for fish meal, which is used as feed for pigs and poultry or as fertilizer.
EFFECT OF RAISING FISHES IN ENCLOSURES
The altimate aim of fish farmers is to make profit from their fish farming business. Most fish farmers are less concern about the well being of the fishes they rear. Fishes like livestock also need proper management to survive. Most fish farmers house their fishes in crowded and cramped conditions with little room to move. Fish may suffer from lesions, fin damage and other debilitating injuries. The overcrowded and stressful conditions promote disease and parasite outbreaks—such as sea lice—that farmers treat with pesticides and antibiotics. The use of antibiotics can create drug-resistant strains of diseases that can harm wildlife populations and even humans that eat the farmed fish. Juvenile fishes can be fed upon by adult fish. Also, mixed farming of different fishes might be difficult to practice except with proper consultation with experts in the field of aquaculture.
High stocking densities can result in a significant amount of pollution from fish excrement and uneaten food, which in turn lead to poor water quality high in ammonia and low in oxygen. Fish farms can also attract predators such as birds snakes, and even theft. In Nigeria, most fish farmers losses their fishes during high rainfall when protective measures are not put in place round the pond.
Also, fish pond constructed close to water bodies can bring about great losses. When pollutants from industries, and pesticides from farms etc are washed into such water bodies which are source of water for the ponds, losses can occur on the fishes.
But also, the positive side of raising fishes in ponds is magnanimous. Fishes grow faster, they are easy to manage and harvest. Visitation by veterinary can help a lot in getting massive harvest etc.
THE BENEFITS OF FISH FARMING IN NIGERIA
1. Increased Food Security: fish farming can help reduce the country’s dependence on imported fish. Most fishes sold in the country are imported from foreign countries like China. When fish production and processing industries improve, the country will no longer rely on imported fish and their products.
2. Employment opportunities : The aquaculture industry has the potential to create more than 600,000 jobs in Nigeria. Young graduates, retirees and job seekers can benefit by venturing into fish farming. fish farming does not require large areas of land and can be done in small ponds, unused tanks etc. Very little investment is required to set it up.
3. Improved Health and Nutrition: There are many benefits of eating fish, they are good source of protein, vitamins, minerals, and omega-3 fatty acids. Fish is a healthy source of protein and can help reduce the risk of heart disease, cancer, and diabetes. It is also used in livestock feed compounding to meet the animals protein requirement
4. REVENUE GENERATION :According to data from the United Nations’ Food and Agriculture Organization (FAO), fish is the most traded edible fishery product in the world, with a total value of more than US$89 billion. If Nigerian farmers can increase on their production, fishes might become a huge generation of revenue like the oil sector in Nigeria
5. Environmental friendly : Growing fish in ponds and tanks instead of in the ocean has several environmental benefits. Since fish in ponds and tanks are fed less, they excrete less nutrients, which means there is less nutrient pollution in the environment.
6. Improved Nutrition of Fish: Feed is an important input for sustainable fish production. Generally, fish farmers use commercial feed to meet the nutritional needs of the fish. But with increasing prices of fishmeal, which is made from small fish species and used as feed, fish farmers are looking for cheaper alternatives.
7. Investment: The fish industry in Nigeria is a place where people can invest their money. .. People can set up feed mills where fish meals are of great importance for livestock feed. Also, more aquaculturist now demand for more fish feeds.
Another profitable investment in the Nigerian fish farming industry is hatcheries. Fish hatcheries produce fish fingerlings and eggs for fish farmers. Also, people can invest in technology used in the fish farming industry. For example, water filtration systems, water recycling system, medicines etc which are used in aquaculture.
MANAGEMENT PRACTICES IN AQUACULTURE
1. HOUSING: fish farmers uses different means to raise their fishes. Such are constructed earthen ponds, concreted ponds, aluminium and plastic tanks, etc.
2. FEEDING: Compounded fish feeds are sold in local markets to meet the nutritional needs of the fishes from juvenile to adult stage. These feeds are produced in pellet form and with various sizes and nutrient content based on the size of the fishes.
Source of clean water must be available at the farm as fishes live in water. The water must not be polluted so that enough oxygen (DO) would be available for the fishes to survive.
There are three types of fish food: natural, supplementary and complete feeds
a) Natural food is found naturally in the pond. It may include detritus, bacteria, plankton, worms, insects, snails, aquatic plants and fish. Their abundance greatly depends on water quality. Liming and fertilization, particular organic fertilization, can help you to provide a good supply of natural food to your fish.
b) Supplementary feeds are feeds regularly distributed to the fish in the pond. They usually consist of cheap materials locally available such as terrestrial plants, kitchen wastes or agricultural by-products.
c) Complete feeds may also be regularly distributed. They are made from a mixture of carefully selected ingredients to provide all the nutrients necessary for the fish to grow well. They are usually make inform of pellets which the fish can easly eat and digest. These feeds are expensive to buy.
Fish system of production can be defined according to the type of food given to the fish:
extensive: fish production depends entirely on natural food; this include detritus, bacteria, plankton, worms, insects, snails, aquatic plants and fish.
semi-intensive: fish production depends on both natural food and supplementary feed; more fish may be reared in the pond;
intensive: fish production depends entirely on complete feed, and the stocking rate no longer depends on food availability but on other factors such as water quality.
Fishes should be fed ones in a day. And five times in a week. This is because they have assess to natural foods that would enhance their growth.
3. MEDICATION
It is important for all fish farmers to consult a veterinarian and experts in the fish industry before embacking on fish farming. They will also advise on measures to take and prevent any form of disease outbreak among the fishes. Water is a substance for easy transmission of diseases among organisms. And adhere to every precautionary measures stated by the experts.
4. DETERMINATION OF DISSOLVED OXYGEN IN PONDS
Low dissolved oxygen concentration is recognized as a major cause of stress, poor appetite, slow growth, disease susceptibility and mortality in aquaculture animals. Daily low dissolved oxygen concentration in pond culture systems is a great concern to fish farmers
Dissolved-oxygen levels can be high during the day period, but the fish species are affected by lowest dissolved oxygen concentration during the night.
literature review conducted by scientists had revealed that the growth of fish at different minimum daily dissolved oxygen concentrations is impaire their growth.
The review indicated that at concentrations below 50 percent of saturation, growth rates declined and became progressively less as the minimum dissolved-oxygen concentrations decreased. At a water temperature of 26 degrees-C, freshwater at 50 percent oxygen saturation contains about 4 mg/L of dissolved oxygen. This concentration is probably higher. Realistically it can be maintained in the early morning in most warmwater aquaculture ponds.
FISH FARMING TECHNIQUES
Fish farming technique is how the fishes are raised. They are:
1. Open Fish Farming Technique
The breeding of fish in natural waterways is known as open sea-cage Fish Farming. In various habitats, including freshwater rivers, brackish estuaries, and coastal marine zones, open systems are being introduced. Floating mesh cages of various mesh sizes are used in growing fish in the water bodies
2. Semi-closed Fish Farming Technique
Semi-closed Fish Farming is when a fish species are grown in a pond with water flowing into the pond from nearby natural river. Wastewater is discharged from the ponds into the nearby river. The farm is supplied with new water pumped back into circulation. This system makes the most extensive use of pond systems.
3. Closed Fish Farming Technique
The raising of fish species in raceways, tanks, and ponds is called closed system fish farming. Water is recirculated via filtering processes and returned to the aquaculture system using recirculation technology. This method helps to keep water quality high while minimizing contact with natural streams.
FISH FARMING SYSTEMS
There are two primary types of fish farming systems : the Extensive and Intensive Fish farming systems.
1. Extensive System
An extensive system is built on a semi-natural habitat (for example, existing ponds) with a natural food source for the farmed fish. By “fertilizing” the pond, the system’s food production may be boosted. In addition, stocking the ponds with a variety of species that inhabit different biological niches helps to preserve the system’s natural equilibrium. E.g., tilapia.
2. Intensive System
Closed-circulation tanks or flow-through raceways are common in intensive systems (e.g., trout farming). Floating sea cages, on the other hand, are intense systems that are exposed to nature. These systems have strict controls over oxygen, water purity, and food supply. Water filtration systems in closed-circulation tanks are complicated.
The intensive system is expensive and requires a high level of monitoring and knowledge to manage properly.
HARVESTING OF FISH
Fishes in ponds are usually harvested with harvesting tools based on the size of the pond. Large size ponds require cast nets to harvest the fishes. Fishes in small concreted ponds and tanks can be harvested using scoop net or bag nets.
To harvest the fishes, the pond must be drained off water so that total harvesting can be done unless smaller fishes are not ready to be harvested.
PROCESSING/ MARKETING OF FISH
Fish farmers can sell fish to fishmongers or industries that convert harvested fishes to fish Products. Some fishmongers sell smoked fishes, sun-dried fishes etc. Fingerings are usually harvested and sundries to make fish meals for feed meals.
Fish scales are used for making beautiful ornaments on bags, shoes and to make decoration.
In conclusion, certain essential factors must be embarked upon to have a successful and profitable fish farming enterprise
ESSENTIAL FACTORS FOR SUCCESSFUL FISH FARMING
For successful fish farming, it is crucial to focus on five major factors so that it can be a successful farming enterprise. Through optimization of each of these factors, profitablity and sustainable operation will be ensured.
1. WATER QUALITY MANAGEMENT: Maintaining optimal water quality is fundamental to the success of the farming enterprise. Parameters to monitor and control include: pH, hardness, ammonia, and nitrite levels. Additionally, attention should be paid to the microbial and bacterial load so as to prevent disease outbreaks and ensure a healthy environment for the fish farming enterprise.
2. BROODSTOCK SELECTION: The health and maturity of the broodstock are critical for producing high-quality offspring. Only mature, healthy, and infection-free female and male fish should be selected. Strong broodstock are more likely to produce viable eggs and resilient fry, which are essential for a successful harvest.
3. EFFECTIVE FRY MANAGEMENT: Proper management of the fry is vital during the early stages of development. It is important to implement a daily routine that includes siphoning waste and running a flow-through system in the pond construction. Consistent and timely management practices will significantly reduce stress and mortality rates, leading to higher yields.
4. HATCHERY DESIGN: The physical structure and design of the farm hatchery play a significant role in its efficiency and profitability. A well-designed facility can streamline operations and improve overall productivity. Farmers should consider hiring a professional to design the farm hatchery so that it meets industry standards and supports the long-term business goals.
5. FEED QUALITY: The quality of the feed directly impacts the health and growth of the fish. It is essential to use high-quality, non-adulterated feed. To avoid low-grade products, purchase the feeds from reputable sources with a proven track record. Using the right feed will lead to faster growth and healthier fish and maximizing the return on investment.
COMMON FISH DISEASES
70% of fish diseases are caused by bacteria, parasites (like protozoa and worms), viruses, and fungi, often triggered by poor water quality, stress, or overcrowding. Farmers loose a lot due to these diseases, including: Ich (white spot disease), Velvet (dusty yellow spots), Columnaris (discolored patches and frayed fins), Holes in the Head, and Dropsy (bloating and protruding scales), which can be caused by bacterial infections.
But today, several methods have being developed to prevent and treat these diseases in infected ponds. The prevention relies on maintaining excellent water quality, avoiding stress, and quarantining new fish.
Also, control and treatment measures can be taken. These ranges from use of local herbs to use of medications. For example:
Ii. Salt: This is referred to as the farmer’s first aid kit. It is cheap and also a multi-purpose medication in ponds.
ii. Herbal remedies: This involves the use of local materials like bitter leaf, neem, garlic, ginger etc to give a supportive treatment.
CAUSES OF FISH DISEASES
i. POOR WATER QUALITY: High ammonia, nitrites, or other toxins stress fish and make them more susceptible to disease.
ii. STRESS: Handling, overcrowding, or poor tank conditions can weaken a fish’s immune system.
iii. INFECTIOUS ORGANISMS: Viruses, bacteria, fungi, and parasites are always present to some degree, but disease flares up when the fish’s defenses are down.
Some of these diseases include:
1. BACTERIAL INFECTIONS ( for example, Aeromonas, Pseudomonas)
Common Bacterial Diseases
i. DROPSY: A bacterial kidney infection causing fluid buildup, bloating, and protruding scales.
ii. HEMORRHAGIC SEPTICEMIA: Caused by infection, it leads to internal bleeding, hemorrhaging of skin and muscle, and bloated abdomens.
iii. GILL ROT: A disease where gills appear wax-yellow or mud-gray, often seen in common carp.
iv. HYDROPSY (WATER’S BELLY): Bacterial inflammation of the liver and intestines, leading to belly expansion and kidney damage.
v. AEROMONAS BACTERIA
This bacteria cause various diseases in fish, particularly in freshwater environments, including motile aeromonad septicemia and furunculosis.
Common Aeromonas-related fish diseases include:
i. MOTILE AEROMONAD SEPTICEMIA (MAS): Caused by motile Aeromonas species like A. hydrophila. MAS is characterized by skin ulcers, red patches (hemorrhages), and an enlarged abdomen.
ii. FURUNCULOSIS: Caused by the non-motile Aeromonas salmonicida. It is a well-known disease in salmonids and other fish, leading to large skin abscesses (furuncles) and internal organ lesions.
FACTORS THAT CONTRIBUTE TO THE DISEASE INFECTION
i. STRESS: Environmental stressors like poor water quality, overcrowding, and improper handling make fish more susceptible to infection.
ii. INJURY: Physical trauma to the fish can create entry points for the bacteria, leading to secondary infections.
iii. POOR WATER QUALITY: Low dissolved oxygen levels, high ammonia, and high nitrite can weaken fish and promote bacterial growth.
SYMPTOMS OF AEROMONAS INFECTION
These pathogens can cause external or internal infection, leading to symptoms like skin ulcers, hemorrhagic spots, fin erosion, and abdominal swelling, especially in stressed or overcrowded fish.
a. EXTERNAL
These include; Skin ulcers, hemorrhagic lesions (red spots), detached scales, pale or red gills, ragged fins, and “popeye” (exophthalmia).
b. INTERNAL
These include; abdominal swelling, internal hemorrhages, and enlargement of organs such as the liver, spleen, and kidney.
PREVENTION AND TREATMENT:
PREVENTION
Prevention involves maintaining good water quality and proper management.
i. GOOD WATER QUALITY: Maintain proper dissolved oxygen, pH, temperature, and low levels of ammonia and nitrite.
ii. STRESS REDUCTION: Avoid overcrowding and ensure proper nutrition and handling.
TREATMENT
This may involve usage of antibiotics or, ideally, probiotics to boost immunity and inhibit Aeromonas growth.
i. ANTIBIOTICS: Certain antibiotics can be used, but their overuse can lead to dysbiosis and increased susceptibility to pathogens.
ii. PROBIOTICS: Some beneficial bacteria, like Bacillus subtilis, can inhibit Aeromonas growth and boost the fish’s immune system.
2. PSEUDOMONAS SPECIES
This bacteria causes a bacterial infection in fish known as Pseudomoniasis, a serious disease that results in significant economic losses due to high mortality rates and poor fish health.
CAUSES OF PSEUDOMONAS
Pseudomonas is part of the normal aquatic microflora caused by factors that lead to stress, such as; overcrowding or poor nutrition. It is an opportunistic bacteria which become pathogenic.
CAUSATIVE AND CONTRIBUTORY FACTORS
i. OPPORTUNISTIC PATHOGEN: Pseudomonas bacteria are often opportunistic, meaning they only cause disease when a fish’s immune system is weakened by stressors.
ii. COMMON STRESSORS: Poor environmental conditions, such as overcrowding and poor nutrition, are common factors that allow Pseudomonas aeruginosa and other species to thrive and cause infection.
SIGNS AND SYMPTOMS
The pathogen lead to internal and external symptoms such as skin lesions, ulcers, internal organ damage, red patches, fin rot, swollen abdomen and sudden deaths.
i. EXTERNAL SIGNS: Fish may exhibit skin discoloration, detached scales, fin and tail rot, and abdominal distension.
ii. INTERNAL SIGNS: Internally, the disease can cause liver necrosis, kidney congestion, and an inflamed or distended swim bladder, leading to lethargy and erratic swimming.
DIAGNOSIS (low-cost):
i. Check behaviour (loss of appetite, sluggishness).
ii. Press belly gently – yellowish/bloody fluid may ooze, meaning infection.
IMPACT ON FISH
i. ECONOMIC LOSSES: Pseudomoniasis is a major cause of high mortality rates in farmed fish, leading to substantial economic losses for the aquaculture industry.
ii. WIDESPREAD PROBLEM: These bacterial pathogens affect a wide range of fish species and are a significant threat in fish farms globally.
GENERAL TREATMENT FOR THE BACTERIAL INFECTIONS
These are the cheapest treatment methods.
i. Salt bath (2–3g/L for 5–10 mins). This gives stress relief and also mild antibacterial.
ii. Bitter leaf or neem extract in pond . A natural antibacterial, cheap.
iii. For severe condition: oxytetracycline (farm supply store) mixed into feed for 5–7 days.
3. PARASITIC INFESTATIONS (PROTOZOA, FLUKES, LICE)
Parasitic infestations are a significant cause of disease in fish, caused by organisms like protozoans, worms (helminths), and crustaceans that live on or in the host fish.
TYPES OF PARASITIC INFESTATIONS
(COMMON PARASITIC DISEASES )
i. ICH (WHITE SPOT DISEASE): Small, white spots appearing on the fish’s body and fins.
ii. VELVET: A protozoan parasite that gives the skin a dusty, gold- or rust-like appearance.
iii. HEXAMITIASIS (Hole in the Head): A protozoan parasite causing holes in the head, often appearing as craters.
iv. LICE AND FLUKES: External parasites like dark, flat spots (lice) or flatworms (flukes) that cause scratching and mucus layers.
v. PROTOZOAN PARASITES: This includes organisms like ciliates, flagellates, and myxozoans that can cause a variety of issues, from external skin and gill problems to internal tumor-like masses and tissue invasion.
vi. HELMINTHS (WORMS): This category includes tapeworms (cestodes), flukes (trematodes), and roundworms (nematodes), which can infest the internal organs of fish.
vii. CRUSTACEANS: Larger parasites like leeches and crustaceans also infect fish, often attaching to the skin or gills.
DIAGNOSIS:
i. Check gills/skin under a cheap handheld microscope.
ii. White spots or moving organisms means parasites infestation.
SIGNS AND SYMPTOMS
These parasites causes symptoms like fish rubbing against pond walls, slimy body, clamped fins, pale gills, lethargy, weight loss, emaciation, poor growth, and excessive mucus production. and mortality. These infections can lead to significant losses in aquaculture and can sometimes transmit to humans through the consumption of raw or undercooked infected fish.
The disease can also cause internal and external damage, depending on the parasite. These damages can include: skin lesions, external cysts, or tumor-like growths on internal organs.
It can also increase the susceptibility to other diseases such as:
i. Parasitized fish may be stressed, making them more vulnerable to bacterial and viral infections.
ii. ZOONOTIC RISKS (HUMAN INFECTION): Some parasites found in fish are zoonotic, meaning they can infect humans. This usually occur when the fish are consumed raw, undercooked, or improperly preserved fish containing the larval stages of the parasite. Examples include anisakiasis (from nematodes) and diphyllobothriasis (from tapeworms).
PREVENTION AND TREATMENT
i. GOOD HUSBANDRY: Maintaining proper water quality, managing fish density, and avoiding overcrowding can help prevent outbreaks.
ii. QUARANTINE: New fish should be quarantined to prevent the introduction of parasites into existing populations.
iii. Affected fish can sometimes be treated with antiparasitic medications, but prevention and prompt removal of infected individuals are often key.
iv. SALT TREATMENT (2–3g/L pond application). This kills many external parasites.
v. FORMALIN DIP (very low dose) if available and affordable.
vi. Prevent by drying/liming ponds between cycles.
vii. FOOD EXPENSES: For human health, thorough cooking of fish or proper freezing protocols is essential to kill parasites and prevent infection.
Some other parasitic diseases include;
i. YELLOW GRUB: A parasite, Clinostomum marginatum, that forms cysts in the muscle tissue of fish.
ii. FRESHWATER VELVET: A parasitic disease that can coat the fish’s body in a yellow or rust-colored dust, causing symptoms like labored breathing and loss of appetite.
4. FUNGAL INFECTIONS (SAPROLEGNIA)
Saprolegnia belongs to a group of organisms called oomycetes, which are not technically true fungi but share many similar characteristics. It is a genus of water molds that causes a destructive, chronic fungal disease in fish and other aquatic animals known as saprolegniasis, or “cotton-wool disease”. This infection is characterized by white, cotton-like patches on the skin and gills and can affect fish at all life stages, from eggs to adults, leading to severe financial losses for aquaculture.
CAUSATIVE AND CONTRIBUTORY FACTORS TO OUTBREAKS
Stressors like low water temperature, poor water quality, and handling can predispose fish to this opportunistic fungal infection, which often also involves secondary bacterial infections.
a. ENVIRONMENTAL STRESSORS: Low water temperatures, temperature shocks, and poor water quality are major triggers for outbreaks.
ii. HANDLING STRESS: The stress from handling fish during transport or tank maintenance can weaken their immune system.
iii. HIGH FISH DENSITY: Crowding in fish farms creates an environment where the disease can spread rapidly.
iv. SECONDARY INFECTIONS: The damage caused by Saprolegnia can allow pathogenic bacteria and other parasites to infect the fish, worsening the condition.
DIAGNOSIS: Easy to see visually.
SIGNS AND SYMPTOMS.
i. Cotton-like white/grey patches on skin, eggs or gills, or eyes
ii. Skin lesions
iii. Lethargy and loss of appetite
iv. Loss of equilibrium
v. oomycete or water mold:
It causes external infections: The fungus grows as filamentous hyphae, creating visible white, grey, or brown cotton-like tufts on the skin, fins, and gills of affected fish.
vi. EGGS INFECT : Saprolegnia readily attacks dead, injured, or unfertilized fish eggs, rapidly engulfing healthy eggs in a hatching unit.
vii. MORTALITY: Infected fish often become lethargic, may lose equilibrium, and can die if the infection is severe enough to cause significant tissue damage or systemic disease.
Massive mortality, especially in young fish and eggs may also occur.
TREATMENT:
i. Salt bath or potassium permanganate (KMnO₄, 2–3mg/L) for 30–60 mins.
ii. Remove dead/weak fish quickly to stop spread.
5. VIRAL INFECTIONS (for example, IRIDOVIRUS, VIRAL HEMORRHAGIC DISEASE)
Viral infections are a significant type of disease affecting fish, caused by various virus families such as rhabdoviruses, herpesviruses, and iridoviruses. These diseases, including Viral Hemorrhagic Septicemia (VHS) and Koi Herpesvirus Disease (KHVD), can lead to symptoms like lethargy, pale gills, hemorrhages, and mortality, and are managed by preventing the movement of infected fish and equipment between bodies of water.
COMMON VIRAL DISEASES IN FISH PONDS
Several viral diseases are well-known in fish:
i. HERPESVIRUSES: Include Carp Pox and Koi Herpesvirus Disease (KHVD), which is caused by the Cyprinid herpesvirus 3 (CyHV-3).
ii. RHABDOVIRUSES: Such as the Spring Viremia of Carp Virus (SVCV), which affects carp.
Iridoviruses: Includes diseases like Viral Erythrocytic Necrosis (VEN), where viruses are seen in the fish’s red blood cells, and Red Sea Bream Iridoviral Disease (RSIVD).
iii. OTHER VIRUSES: Other important viral agents include Infectious Pancreatic Necrosis Virus (IPNV), Infectious Hematopoietic Necrosis Virus (IHNV), and Salmonid Alphavirus (SAV), according to the Food and Agriculture Organization (FAO).
SYMPTOMS AND DIAGNOSIS
Symptoms of viral infections are often non-specific but can include:
i. Lethargy and anorexia (loss of appetite)
ii. Darkening of the skin
iii. Abnormal swimming behavior, such as spinning
iv. Increased respiration and pale gills due to anemia
v. Internal hemorrhages, or blood spots, on organs like the heart and kidneys
vi. Ulcerations on the skin
vii. Mortality, which can be high in outbreaks
PREVENTION AND MANAGEMENT
Preventing the spread of these viruses is crucial:
i. AVOID MOVEMENT OF FISH: Do not move fish between different water bodies to prevent virus transmission.
ii. DISINFECT EQUIPMENT: Clean and disinfect boats, fishing gear, and live wells, as viruses can survive on wet surfaces.
iii. QUARANTINE NEW FISH: Isolate new fish before introducing them to existing populations to ensure they are healthy.
iv. MONITOR WATER QUALITY: Maintain good water quality, as environmental stressors can increase a fish’s susceptibility to infection.
v. VACCINATION: Vaccines are available for some viral diseases, such as KHVD.
IRIDOVIRUS
This is a family of viruses that causes severe diseases in fish, leading to high mortality rates in both cultured and wild stocks of various freshwater and marine species. These diseases, particularly those caused by megalocytiviruses, can result in significant economic losses in the aquaculture industry, affecting fish like ornamental gouramis, grouper, and sea bream. It also affect dwarf cichlids.
TYPES OF IRIDOVIRUS
The family Iridoviridae includes several genera of fish viruses, with megalocytiviruses being a particularly important group causing systemic infections. Examples include Red Sea Bream Iridovirus (RSIV) and Infectious Spleen and Kidney Necrosis Virus (ISKNV).
TRANSMISSION
The virus can spread horizontally through contact and through waterborne transmission.
SYMPTOMS
Symptoms can include anemia, lethargy, enlarged organs like the spleen and kidney, and sometimes visible growths. All these are systemic infections. In some cases, like lymphocystis, wart-like growths can appear on the skin or fins.
PREVENTION AND CONTROL
There is no specific cure for a viral infection, so prevention and management are crucial.
Some methods used to prevent and control the infection include: improving water quality, ensuring good nutrition, reducing stress, and practicing quarantine and good biosecurity on farms.
IMPACT OF THE DISEASE
Iridovirus infections are a major threat to the aquaculture industry, causing substantial economic losses and high mortality rates in affected fish populations.
VIRAL HEMORRHAGIC SEPTICEMIA (VHS)
This is a highly contagious and often fatal viral disease caused by VHSV (Viral Hemorrhagic Septicemia Virus) that affects many freshwater and marine fish species, including salmon, trout, and walleye. It can affect more than 40 different fish species, including important commercial and recreational species such as: salmon, trout, yellow perch, walleye, muskellunge, and northern pike.
TRANSMISSION
VHS is highly contagious and can be spread through several means:
i. MOVING INFECTED FISH: Transporting fish from one body of water to another can spread the virus.
ii. CONTAMINATED WATER: Moving water from an infected source can transmit the virus.
iii. CONTAMINATED EQUIPMENT: Boating equipment, fishing gear, and vehicles that have come into contact with infected water or fish can carry the virus.
iv. CONTAMINATED BAIT: Using frozen or live bait from affected areas can introduce the virus to new water bodies.
DIAGNOSIS:
laboratory tests: This is highly expensive for small farmers to carry out.
SIGNS AND SYMPTOMS
The symptoms can include; hemorrhages, bulging eyes, and a swollen abdomen. The disease is a threat to fish populations, with transmission primarily through moving infected fish, contaminated water, or equipment. It is not a threat to humans who handle or eat infected fish.
Some other symptoms of VHS include; reddish bruising on the body, gills, eyes, and fins.
Bulging eyes (“pop-eye”).
Swollen, fluid-filled abdomens.
Darkened coloration,
abnormal swimming behavior.
PREVENTION
Preventing the spread of VHS is crucial, and can be achieved by:
i. CLEANING EQUIPMENT: Thoroughly cleaning boats, trailers, and fishing equipment before moving to a new body of water.
ii. PROPER DISPOSAL OF BAIT: Disposing of used bait fish in the trash instead of throwing them back into the water.
iii. AVOIDING MOVING FISH: Not moving live or dead fish from one water body to another.
iv. QUARANTINING NEW FISH: Implementing strict quarantine procedures for incoming fish in aquaculture settings
TREATMENT:
i. No cure (mostly), but farmers are advised to focus on prevention.
ii. Quick water flush and disinfection.
iii. Burn/deep bury dead fish immediately.
iv. Restock only after disinfection and pond drying.
6. NUTRITIONAL/LIVER PROBLEMS (FATTY LIVER, YELLOW BELLY)
FATTY LIVER (HEPATIC STEATOSIS)
This is a well-recognized disease in fish, especially in aquaculture, caused by excessive fat accumulating in liver cells. It can stem from high-fat or high-carbohydrate diets and nutritional deficiencies, leading to impaired growth, reduced disease resistance, and mortality.
CAUSES
i. HIGH-FAT DIETS: Incorporating excessive lipids into a fish’s diet is a primary cause of fatty liver in cultured species.
ii. HIGH-CARBOHYDRATE DIETS: High-starch diets can also lead to fatty liver, sometimes referred to as carbohydrate-induced hepatic lipidosis.
iii. NUTRITIONAL DEFICIENCIES: Lack of essential nutrients like choline, carnitine, and certain vitamins can predispose fish to fatty liver disease.
iv. DIETARY ADDITIVES: Including toxic non-essential fatty acids in feed can cause liver issues.
SYMPTOMS
In fish, the symptoms include; a pale, swollen, or discolored liver.
i. LIVER DISCOLORATION: Affected livers may appear yellow, light brown, or milky white.
ii. LIVER ENLARGEMENT: The liver can swell and show rounded edges.
iii. FRAGILITY: In some cases, the liver can become fragile.
iv. BEHAVIORAL CHANGES: Diseased fish might experience a loss of appetite, reduced movement, or listless swimming.
TREATMENT
i. DIETARY ADJUSTMENTS: Correcting the diet by reducing high-fat or high-carbohydrate ingredients and incorporating essential nutrients can help.
ii. NUTRITIONAL SUPPLEMENTS: Adding carnitine, choline, unsaturated fatty acids, or specific plant extracts to the diet can improve liver health.
iii. SELENIUM: Including selenium (nano selenium and organic selenium) can be beneficial.
IMPACT
i. REDUCED HEALTH AND GROWTH: Fatty liver disease negatively impacts a fish’s growth, immune function, and overall metabolic health.
ii. INCREASED MORTALITY: The condition can be severe and even lethal for farmed fish.
iii. AQUACULTURE SUSTAINABILITY: Fatty liver disease is a significant challenge to the sustainable development of the aquaculture industry.
YELLOW BELLY
This is not a single and specific fish disease, but rather, conditions like jaundice in catfish, which causes yellowing of the skin, eyes, and fins due to excess bile pigments. It can also refer to yellow grub parasitism in various fish species, impacting reproduction, or a symptom of Columnaris disease where gills turn yellow/brown. The term might also describe a freshwater velvet parasite on a fish’s body or even be a common name for specific fish species like the Golden Perch.
DIAGNOSIS:
Linked to poor feed or overfeeding.
SYMPTOMS
“Yellow Belly” as a fish disease show signs of Jaundice (Catfish Jaundice), which is a serious condition in freshwater catfishes marked by the yellow discoloration of skin, eye sclera, and fin bases due to an excess of bile pigments in the blood and lymph, leading to hemolytic anemia.
They also show signs of yellow abdomen, weak fish, slow growth, deaths without obvious wounds.
PREVENTION AND TREATMENT
i. QUARANTINE: Isolate the affected fish to prevent potential spread to other tank mates.
ii. PROVIDE CLEAN WATER: Conduct water tests and perform a water change to maintain pristine water conditions, as poor water is a common trigger for disease.
iii. CONSULT A VET: Seek advice from a qualified veterinarian or aquatic specialist for a proper diagnosis and treatment plan.
iv. OBSERVE AND TREAT: Monitor the fish closely for other symptoms like lethargy, loss of appetite, or erratic swimming, and administer the recommended medication as directed.
v. SWITCH immediately to quality feed (check expiry, avoid oily or moldy feeds).
vi. Add bitter leaf extract (cheap liver tonic) to water.
viii. Salt treatment to detoxify stress.
GENERAL PREVENTIVE MEASURES
Maintain proper water quality, avoid overstocking, quarantine new fish, and feed a balanced diet to support fish immunity.
GENERAL SYMPTOMS TO WATCH FOR
It is important for every fish farmer to carry out the following:
i. Observe daily: Early detection saves money. This is achieved through frequent observation of the fishes in the pond to identify disease infection and preys entering the pond.
ii. Keep a logbook : This helps to link disease outbreaks to feed, water, or weather changes.
These will help the farmer to identify the following challenges in his pond quickly.
Some of the general signs to watch out for include:
i. Changes in behavior (lethargy, rubbing against objects, fin twitching)
ii. Physical signs (white spots, dusty patches, bloating, protruding scales, holes)
iii. Changes in appetite (loss of appetite, weight loss)
