Fish health and profitability 

Since 60 to 80% of the production cost of a fish farm is in feed, an important factor for a successful tilapia farm is the feed conversion ratio (FCR). The FCR is the metric that shows how much feed has been used to grow a certain volume of fish. Though the FCR is focussed on feed, fish health significantly impacts the outcome. Consider the following situation:

Fish farmer Julie stocked 10,000 fingerlings 5 months ago. She has diligently fed them with high quality feed on which she spends about 5 million shillings. She expects to harvest it in 2 months. Today she woke up and found about half of her fish dead, floating in the pond. Now she will only harvest half of the anticipated amount of fish. When she calculates her FCR it will be extremely high, because all the feed that she has fed the dead fish gets included in the FCR calculation. It is highly unlikely that she will be able to return a profit for the production cycle.

This goes to show that fast growth needs to go hand in hand with health on a farm. When an animal dies before harvest all the resources invested in growing it are wasted. Similarly, the slow growth rate of fish on farms has a major impact on profitability and productivity. If farm-raised fish take longer to reach maturity, fewer fish can be harvested within a given timeframe, leading to reduced profits for the farmer. Additionally, the longer a fish takes to reach harvest size, there are increased costs for feed and other resources needed to properly care for the fish during the extended period of time. As such ensuring the health of your fish population is important for every fish farmer.

First signs of bad tilapia health

The first signs of sickness can be difficult to spot in your tilapia population because signs of bad tilapia health start small – with slight changes in their behavior and in how they look.  As such it’s important that your team keeps a keen eye out for the aspects listed below. By recognizing any potential signs or symptoms of diseases, farmers are able to quickly diagnose and treat the issue before it has a major impact on the farm.

Behavioral warning signs:

1. Decreased appetite 
2. Abnormal swimming behavior, such as swimming erratically or staying at the surface of the water 
3. Listlessness, lethargy and unresponsiveness to stimuli 
4. Rubbing or flashing against objects in the tank 
5. Increased mortalities 

Appearance warning signs:

1. Change in coloration; including dermal erosion, ulceration, lighter color patches on the tilapia body, rashes.
2. Pale gills 
3. Cloudy eyes 
4. Clamped and/or discolored fins or other physical abnormalities 
5. Unusual lumps or lesions on the body

As you can see some of these things will be more obvious than others, but overall they require a good understanding of the fish in order to be able to know what’s normal and what is not. To ensure early detection it is therefore important that daily records are kept about feeding behavior and the other parameters, so that changes are noticed early on. Key records to keep include farm diaries and feeding logbooks, sampling and health inspection forms. 

The 3 pillars of fish health: The environment, the fish and pathogens

The environment-fish-pathogen triad is an important concept for fish farmers to understand. This concept describes the intricate relationship between the fish, the aquatic environment and aquatic pathogens which together determine the health and growth rate of the fish. 

1. The fish

Not every fish is the same. There are significant differences between species, and even within a type of species you have good and bad quality fish. As such it is crucial to 1) understand your chosen species of fish and 2) ensure high quality fish. To understand your fish it is important to read up your chosen species of fish and what conditions it needs to thrive. With this knowledge you can assess if the species is a good fit for your farm and for your ambitions. 

Once you are confident that the species will work for your farm setup, you need to ensure that you purchase high quality fingerlings. Afterall, the fingerlings are your future harvest. As such you want to look for healthy and active specimens. Avoid purchasing any sickly or lethargic looking fish. Also, inspect the color of the fish to ensure they have a solid color without any fading or discoloration. Take notice if there are any visible signs of parasites or infection. Finally, make sure that the fingerlings you purchase are of the right size and age for your intended purpose. Are you not sure where you can get strong and healthy fry? The Aquaculture Support Center is happy to put you in touch with a reputable hatchery near you! 

A happy fish is usually a healthy fish. That is why it is important to provide an environment that is comfortable for the fish species and that meets its needs. When this is not the case a fish can get stressed. Stress, just like with humans, reduces the natural immune system of the fish and makes it more susceptible to diseases. Stress is usually highest during specific activities such as transfer, feeding and handling. The following table outlines common times when stress levels are high and how it can be minimized:

2. The Environment

As shown above most causes of stress are coming from their environment. As such, maintaining a healthy environment for your fish is key to their health and growth. The main production environment on a fish farm is the water. Since the fish spend all their time in the same production unit it is important to verify and where possible control the following water parameters to ensure a productive environment for this fish:

1. Temperature: 26-32°C, 27 °C is optimal

(Note: tilapia will slow their eating at 23 °C, will become weak at 16 °C and die at 13 °C)

2. Dissolved Oxygen: 5-7 ppm (parts per million)

3. PH: 6.5-8.5 

4. Free Ammonia (not total ammonia): optimal=0, 2 ppm will kill, 1 ppm will slow growth.

5. Nitrite: 0.3 mg/l or less

6. Nitrate: 200-300 ppm

7. CO2: 20 mg/l or less

8. Chlorine: 0

The environment also includes other organisms that may be present in the area which may affect the fish. This can include plants and algae in or nearby the production unit but also predators such as birds and other fish species. Depending on the exact location, production system and circumstances of the farm some things can be more relevant than others. It is important to be aware of the environment so that you can correctly assess impact and take action as needed to create a conducive environment for your fish. Limiting and where possible eliminating pathogens being introduced to the fish is done by biosecurity. These are common protocols implemented on farms. They range from restricting visitors, to ensuring high quality feed is provided, and reducing contact of the farmed fish population with wild populations.

A key concern for fish farms in Uganda are birds. They can steal fish from production units, can carry disease, and their presence is a stress factor for fish. As such, reducing the presence of birds is important. Here are 4 ways of achieving this.

1. Install predator nets over cages, or single strings over ponds to deter birds.
2. Hang reflective objects such as aluminum pie pans or strips of mylar tape around the farm area to scare away predators. The reflections from these objects can be startling to birds and could cause them to leave the area.
3. Designate one or two persons to regularly patrol the farm and scare away any birds that may be present with a loud noise or sudden movement.
4. Plant decoy plants in strategic locations around the fish farm that can keep birds away from the actual farm location. Examples of these plants include sunflowers, corn, millet and sorghum.  

Proper management of the environment and biosecurity measures are essential for maintaining healthy fish populations and preventing disease outbreaks. 

The importance of proper nutrition in fish health 

Feeding is essential to the health and well-being of fish. Proper nutrition ensures that fish remain in good health, grow adequately, and in the case of broodstock reproduces. Providing a healthy, nutritious feed for fish helps to support their immune systems, promotes growth and reduces stress levels. Nutritional deficiencies can result in disease and poor growth, so it’s important to make sure that your fish are getting all their essential vitamins and minerals through feed. Feed also provides much-needed calories for energy throughout the day. There are roughly 2 types of feed available; complete pelleted feed and farm made feed. 

The pellets are designed with all the nutritional needs of the fish in mind for that specific species and growth stage, providing balanced diets and eliminating the need for guesswork with homemade feeds. Furthermore, pelleted feed also contains important micronutrients such as vitamins and minerals that are essential for the health and well-being of the fish. Pelleted feed is therefore a great way to help improve the resistance of fish to disease in a fish farm. Additionally, the use of pelleted feed reduces wastage due to its easy digestion by fish allowing them to get all their necessary nourishment without having to consume more than needed.

Homemade feed may offer some benefits in terms of cost savings, but it can be difficult to ensure the feed contains all the required nutrients in the right amount for each fish species and the specific stage of growth. The bite size of the feed is also likely to be less than optimum. Lastly, there is more risk associated with homemade feeds as bacteria and other contaminants may be present which can cause health concerns for the fish. In comparison, high quality pelleted feeds are produced in a controlled environment that limits or eliminates these risks, making them a better option when it comes to ensuring the health of your fish.

Proper feeding management is essential for maintaining healthy water quality and preventing diseases in fish. Over-feeding can lead to increased nutrient loads, which can cause water quality to deteriorate, leading to an increase in harmful bacteria and other pathogens. This can cause a rise in the number of parasites or bacteria that cause diseases in fish. Additionally, uneaten food left in ponds lead to an increase in ammonia, which is toxic and can result in poor health for the fish. For this reason, it is important to feed your fish only as much as they can eat within five minutes each day and not overfeed them. Doing this will help keep the water clean and prevent diseases from occurring.

3. Pathogens

Fish can suffer from a variety of diseases, the most common of which are caused by bacterial, viral and parasitic infections coming from the fish’ environment. Bacterial diseases are caused by bacteria entering the fish’s body and multiplying, resulting in infection. Viral diseases are caused by viruses that cause damage to the fish’s internal organs or disrupt their organ functions. Parasitic diseases occur when parasites invade the fish’s body and feed on its blood or other bodily fluids, causing serious health problems. All three types of disease can be difficult to diagnose and treat, making prevention even more important. Proven strategies like quarantine before stocking, vaccinations against disease-causing agents, and proper nutrition can all help to maintain fish health and promote growth. 

Table 2 outlines the six most common diseases in tilapia and their associated symptoms and cures. 

Once a beginning infection is diagnosed, there are a number of treatments available such as disinfection of ponds, flushing of water, and others as shown in the table. Depending on the specific needs of a farm, some treatments may be more effective than others. It is important to get expert advice early on to ensure an outbreak is contained and treated as soon as possible. 

Tilapia farming can be a rewarding and fulfilling experience. Health maintenance is an essential part of owning and operating a tilapia farm, as proper management will help ensure the safety of your fish and the best possible yield. By understanding the diseases that commonly affect tilapia and learning to identify symptoms quickly, you can take swift action when a problem arises. From making sure to have the right monitoring tools in place to having the appropriate treatments at hand if needed, taking a proactive stance on managing your fish’s health will help keep them safe as it pays off in dividends for both you and your business.

Have you had, or are you having challenges with fish diseases at your farm? We would love to hear from you in the comments below or by email!