The fourth infographic of the educational series summarizes some of the basic aspects of fish knowledge and management:
Fish are fascinating creatures: their growth, development and health is influenced by the environmental conditions they are exposed to. Which is why, understanding the basic of fish development and management is essential to nurturing a healthy aquaponics system.
During their maturation phase, carps for example, develop a different stomach size depending on the diet they are exposed to during their initial growth period. If a carp sources its energy and nutrients primarily from plant based material, its stomach will be more elongated. In contrast, if its main food source comes from small invertebrates and other insects, it will develop a smaller stomach as food can be process more readily. This is important to keep in mind when deciding which feed to use throughout fish maturation, as changes in diet could be difficult for them to adapt to afterwards.
There is one environmental parameter fish are not able to easily adapt to, or in better words control: their body temperature. Most fish are ectothermic creatures, which is to say that their body temperature will fluctuate alongside environmental temperature. Humans and other mammals on the other hand, can maintain a constant internal temperature independently of the environment. They are said to be homeothermic creature.
This implies that fish metabolism, the amount of energy they are able to process from the food they eat, and in turn how fast they will grow, will change depending on the water temperature. The colder their environment is, the slower their metabolism.
Although fish can normally withstand a wide variation in temperature, changes in water temperature must be introduced gradually. It is good to also keep in mind that different species have different ranges they can tolerate (e.g. cold water versus warm water fish) as well as different optimal point at which their biology will operate at peak efficiency and therefore grow faster while consuming less food.
The amount of feed required is influenced by many different parameters and may be difficult to calculate if there are unknown variables, for example:
- Number of fish is not known
- Average fish weight is unknown
- Different growth stage or different species
- Fish feed quality and nutrients proportion unknown (e.g. protein, carbohydrates, lipids…)
- Water temperature has changed or is unknown
A simple experiment you can perform is Ad Libitum feeding. Feed you fish as much as they eat readily in 10-15 min and keep a note of that amount. Assuming your water temperature is constant and you are using the same fish feed, you can use this amount to feed your fish on a daily basis.
You will have to repeat this experiment once every month or week (for fry this will have to be more frequent) depending on the growing stage of the fish. The younger they are the faster they grow and the more frequently they will need their food intake adjusted.
Some other environmental conditions to consider are:
- Ammonia and nitrite: Lowest possible level, close to 0 mg/litre as they are toxic at any detectable levels.
- Light and exposure: Fish prefer to be in a more protected and shady environment. They should receive indirect light from the sun to help them to adjust their circadian clock. Direct light should be avoided, to increase their comfort and reduce algae growth. Large variation in light intensity may also induce a stress response, which is detrimental to their growth.
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