Fish food lies at the heart of all successful fish keeping systems from a small tropical aquarium to a vast open lake. A good diet is essential if your fish are to thrive and grow and live a long and happy life. In an aquaponic system food for fish becomes food for plants and ultimately food for filter microorganisms.
The availability of a suitable fish food plays an important role in selecting the best fish for aquaponics. Quite naturally different fish foods are marketed according to the species to be kept. There is however quite a bit of overlap and your shouldn’t assume that just because a fish food is branded a trout pellet that it wouldn’t be an excellent choice for carp, for instance, under certain operating conditions.
Fish food falls into two broad categories, according to the overall aims of the keeper.
a) Best Fish Food for Display
Fish food in this group are for people who want to make sure they show off their fish in the best possible way. They are less interested in growth and production. They nevertheless less must have fish that are active and healthy. Fish dealers and most aquarium systems fall into this group. The majority of garden ponds will also be more interested in this type of fish food. Characteristics of a suitable diet for this situation include;
- lower protein levels as this will reduce the production of wastes.
- reduced wastes lead to clearer water of higher quality.
- lower protein levels will also limit costs and increase fish activity as they seek to obtain adequate nutrition levels
- floating pellets to more detect uneaten food and promote hand feeding
Pond sticks are a very popular type of food for ponds and flakes for aquaria.
b) Best Fish Food for Growth
If you are primarily interested in maximising fish growth make sure that you adopt principles that are common throughout aquacultural enterprises. Fish farmers aim to maximise production by maximising the growth of individual fish and maximise the number of fish that can be kept within a tank or pond. As such they require a fish food that has;
- a high level of protein for greater growth
- a higher oil level to provide more energy and save the protein for growth
- improved digestibility to lower waste product production enabling more fish to be kept.
All the above does involve greater control over the fish and invariably comes at a cost.It is not as simple as maintaining a nice display aquarium for example. So please bear in mind that;
- higher levels of risk require more mechanisation leading to a greater reliance on suitable backup systems, for aeration and filtration
Aquaponic practitioners usually sit somewhere between the two extremes outlined above. Certainly if an edible fish is desired then growth rate is important. However, it is seldom desirably to aim for the sort of intense stocking densities that commercial fish farms operate at. Some where around 20kg/m3 is much more realistic than 60+ kg/m3.
2) Food Quality
If the fish rely on you as their only source of food the quality must be top-notch. In a tropical aquarium the diet must supply all of the fishes needs whereas in a pond, fish are often able to supplement their diet with natural live fish food.
Advances in fish nutrition have improved the nutritional status of many of our favourite fish foods. Always look at the label on fish food products. The first thing to note is the protein content. This is the most expensive component of the formulation consequently manufacturers tend to keep this low. To some extent a higher oil level will compensate for low levels of protein by providing the energy and saving the protein for growth. Different species, and sizes of the same species, of fish have different requirements for protein. Carnivourous fish, such as trout, require more protein than omnivorous species like carp. Smaller fish are more rapidly growing and aways need more protein.
Vitamin and mineral content of fish foods is also very important but, unforunately, difficult to optimise. Most manufactures take a cautionary approach as there is very little useful scientific information available. As a consequence they probably add more than is strictly necessary. Part of the thinking behind this is that these are the constituents that degrade more rapidly with storage . Degradation in vitamin C levels is common.
Colour enhancing compounds are often included in fish diets. The colours of goldfish and koi especially need to be vivid. These substances are usually naturally present in good numbers in plants and algae. Typical colour enhancing additives include;
- shrimp meal
Advances in fish nutrition have improved the nutritional status of many of our favourite fish foods. Always look at the label of food products. Of top concern is the protein content. This is the most expensive component of the formulation so manufacturers tend to keep this low.
Vitamin and mineral content of many foods is difficult to optimise. Most manufactures take a cautionary approach as there is very little useful scientific information available. As a consequence they probably add more than is strictly necessary. Part of the thinking behind this is that these are the constituents that degrade more rapidly with storage . Vitamin C levels are particularly prone to degradation.
3) How much to feed
Above all else, water temperature has a significant and direct influence on how much, and what type of fish food should be used. Temperature directly affects the metabolism of all fish, plants and filter microorganisms. Each will have quite a narrow range where metabolism and growth are optimal. Generally as the temperature drops the amount of food that is required also drops. At some point, during the winter for instance, feeding will stop completely. Most tropical fish will be unable to survive these low temperatures.
For further information on this vital factor please consult my Guide on Pond Fish Feeding Rates.
4) Types of Food
Food manufacturers produce a wide range of different types of food. The main ones, and when to use them, are outlined below.
i) fish flakes
Flakes are, for the most part, ideally suited to small fish that are typical of so many tropical fish tanks. Only small quantities are needed and a range of automatic fish feeders at reasonable cost are readily available.
ii) pond sticks
These have become very popular in resent years. They consist of very light floating extrusions of relatively low protein levels. Fish need to eat a lot of them to get the nutrition they require. They produce little waste and generally help to keep water pollution to a minimum. Hand feeding becomes a riot of activity.
These are popular with commercial fish farmers. They tend to be high in protein and fat, not to mention price. Although expensive per kg. the total weight required is proportionately much lower than a staple formulation. Growth rates of fry are much greater than adults and a highly nutritional diet is invariably the best choice. If water pollution is to be avoided the correct feeding regime is required.
By far the most popular type of commercial fish food. They are easy to handle and work well in automatic fish feeders. Balancing the formulation and cost benefit is critical if commercialisation is an objective. Feed conversion rates are all important and need to be calculated regularly. Fortunately most home fish keepers are less concerned with this level of optimisation.
v) live foods
Live foods are generally of very high quality and can really perk up a shoal of fish. If natural sources are used there can be a substantial risk of introducing disease. Much better, but much more work, is to culture your own. They tend to be of very high protein levels and may show a level of self-degradation once inside the fishes gut that greatly improves digestion. Brine shrimps exhibit this feature and have proven essential for many newly hatched fry species, including carp.
Many fish species are omnivorous and plants play an important role in their diet. Carp, including koi, love plants, so much so that it is usually impossible to keep them both in the same pond. Aquaponics offers great potential to produce a significant proportion of the fishes diet using ‘recycled’ plants such as lettuce and water cress.