If you think of starting aquaponics, there are a few things you need to know about fish keeping. Fish are special animals because they live in water. Some parameters are important to respect. In the below article we will review the specificity of fish biology. Understanding those basics about fish keeping will allow you to grow fish in good conditions. Please make sure to read it until the end to not miss an important information crucial to your fish keeping knowledge.

1. Fish are fragile animals

Your aquatic friends are living in a very low gravity environment. Therefore the structure of their body is not as robust as terrestrial creatures. Fish are soft and their internal organs are fragile. Inside their body, there is a bladder allowing them to control the floatability. If you miss handle your fish and let it fall on the soil, the bladder may burst. Please be careful and manipulate them close to the ground on a soft soil (grass is better than concrete).

2. Water parameters for fish keeping

They breath in the water and multiple exchanges occur between their body and the water they live in. There are plenty of important parameters. The main ones are: Temperature, oxygen, ammonia, nitrite, nitrate and pH. I will not go through each of these parameters in this article but I made several videos on these topics already so please refer to it.

More information about critical water parameters there.

3. Osmosis and fish keeping

There is an interesting phenomenon specific to water called “Osmosis”. This phenomenon create a force constantly pushing the water from the less mineral concentration to the highest mineral concentration. The inside of the fish body is more concentrated than the fresh water they live in. Therefore, the water is constantly pushing to go inside and dilute the mineral concentration. Your future friends will spend a considerable energy regulating the water int heir body. It is called osmosis-regulation. It is possible to increase the mineral concentration into the water in order to minimize the osmosis force on the fish.

More information there.

4. Barriers against disease

We distinguish 3 layers of barriers against disease. :

4.1 Skin

Depending on the species, the skin is more or less thick. The cells of the skin are stronger and form a wall which is a real barrier against disease.

4.2 Scales

Scales are not present on all species. They are attached to the skin and represent a second wall against disease. Scales also act as a shield and represent a protection against physical attacks. Some species present very fragile scales. You therefore need to be very careful when handling your aquatic pets. Never touch them with dry hands. If you do, there is a chance to see the scales sticking to your hands and coming off. It is good practice to wet your hands before any handling.

4.3 Mucus

Mucus is a viscous substance covering the entire fish body. Mucus has several functions. First it helps them to slide into the water and minimize the drag. Secondly it is a physical barrier against disease. While mucus is very effective in terms of disease prevention, it is very fragile. Poor handling practice can remove the mucus away. Never use a dry fabric to hold your fish or the mucus will stick to it and you will leave them without this defense against disease.

For more information about fish disease see there.

5. Gills

Fish are absorbing oxygen through the gills. Situated at the back of the mouth, the gills are the equivalent of our human lungs. They allow the fish to absorb the oxygen from the water. Gills are composed of a multitude of tiny porous blood vessels. In contact with water, those blood vessels allow the oxygen to enter in the blood. Due to their extremely small size and the finesse of the membrane, those blood vessels are extremely fragile. Therefore, handling must be done with high care. The last thing you want to do to keep your fish healthy is to put your fingers though the gills. It would burst the blood vessels and the poor animal would die, losing his blood into the water.

6. Fins

While fins have an important motion function, they are also a very good indicator. Grown in poor conditions (High density), your aquatic pets will present damaged fins. Also fins are generally transparent, it is a good area to check the presence or absence of parasites.

7. Lateral line

When you walk along a river, you see the fish swimming away. They have an efficient ability to feel vibrations. They have receptive organs all along their body. In an aquaponics system, the your future friends will have no ability to swim away. When you walk loudly around the tank, the fish are filling the vibrations. Please take this in consideration as extreme vibrations can stress and eventually kill them.

8. Size of the mouth

Fish species can be placed in different categories in function of their diet. Predators are generally presenting a large mouth. Omnivorous generally have a smaller mouth. When you feed your them, the food size must be adapted to the size of the mouth opening. Make sure your fish are able to fit the pellet in their mouth or they will not eat.

9. Size of the eye

Eyes are actually an excellent indicator of the fish health. A fish grown in poor conditions will sometimes stop growing. However, when the energy is limited, the metabolism will always supply vital organs. Even if they stop growing, the eyes will still receive the energy necessary to their growth. This is the reason why, an old fish grown in poor condition will present a small body but big eyes. If you have to buy fingerlings, avoid the batches with large eyes in relation to their body.

10. Fish behavior

Every species has his own behavior. In other words, some are easier to keep than others. Predators are generally more aggressive and will not tolerate to be mixed with different sizes. From a fish growth perspective, it is generally better to keep species separated and sorted by size. In aquaponics however, many of us enjoy keeping multiple species and try to replicate the diversity of a natural ecosystem. If you are trying to achieve this, make sure that all species are social and able to leave with each other. Alternatively, you may start with 50 fish and finish with only one big fish LOL.

You will probably be interested to discover Jonathan’s six steps to build and manage an Aquaponics system. Click here to access for free! Thanks and good reading 🙂