Feeding your fish

As with other aspects of husbandry, thorough research of your chosen species should be carried out before production starts.  How, when and what to feed the species you are culturing is essential knowledge if you want to be successful in aquaponics or aquaculture. The quality of feed you select not only determines the health of your fish, but also considerably affects the health of your plants. Appropriate feeding is especially important in aquaponics as it is the main determinate of quality and quantity of nutrients available to plants.

When and how often do i feed?

When feeding always remember these tips:

  1. Do not over feed
  2. Observe
  3. Remove uneaten food
  4. Record sheets

A general rule for feeding fish is to only feed your fish as much as they will eat within five minutes. Spread the feed over the surface of the water slowly.  After five minutes, remove the remaining food from the tank with a net. Record how much you have given.

Over time you will be able to judge just how much food to give depending on their behavior, however it is strongly recommended you still watch them eat as this is an ideal time to inspect the health of your fish. Maintaining thorough records of your animals eating habits is invaluable. Over time this record will be able to tell you how if your fish are growing efficiently and allow you to improve production. If something goes wrong, consult your records; have the fish been eating less than they usually do? This may help diagnose your problem.

Generally it is  better to feed little and often, at least twice a day, ideally 3-4 times. You need to remember that you want all of the fish feed you give to be eaten; for two main reasons, firstly because its an expensive and valuable resource and secondly because if its not eaten then it will decompose and have a negative impact on your water quality

If you have different sized fish, and more than one tank, try and “grade” them into their same sizes to ensure they all get a chance to feed and if you have very small fish, you can change the type and size of feed as they grow.

As a final note, whilst your type of fish species will determine the type and presentation of the feed, if you can, its always better to feed a floating pellet as it allows you to have better idea of whats being eaten. As you will find out feeding is a really great opportunity to observe the health, condition and size of your stock, plus it gives a great early warning as to changes in water quality… so if they are not feeding normally, stop feeding, think why, and its often an indication to look further… (air, temp, pH, water quality, oxygen level etc.)

Which food for your fish?

The type of fish that are being grown, the age of the fish and the desired output from the aquaponics system will determine the amount and type of fish food that is used.
There is much choice, for a start: commercially produced pellets and other formulated feeds or homemade diets and even live feeds. A mix of all of the above? Knowing what your species nutritional requirements are and what you would like to achieve from your system will help you make this choice.

Commercial Feed

Providing its fresh and suitable for your intended fish species, then pelleted feeds provide a manageable solution to knowing exactly what you are giving your fish and therefore plants. Depending on whether the fish are omnivorous or carnivorous, they will require different protein levels (trout 45%, tilapia 30%), and depending on the size of fish, different sized pellets. In terms of presentation, they can be floating, slow sinking of fast sinking for bottom feeders.

In larger systems where desired output is high, a specific amount of formulated feed will give the best production possible. For a small system in the back garden, the grower may not require the system to be as productive and will be happy to use a general diet.
These feeds are excellent at providing the full nutritional balance your fish need and are of such consistent quality that the diet can be tailored so the fish to grow as quickly and efficiently as possible. The diets are also produced in such abundance (for the aquaculture industry and aquaria industry) that they are cheap to buy.
There is however often an ethical concern with these diets; many pellets contain high amounts of fish meal and fish oil. This means fish from the wild have been caught just to make the fish diet, sometimes more fish than would be caught in the first place for human consumption!

‘On-farm’ or home-made feeds made from wastes and resources that do not compete with human consumption can decrease the environmental footprint of production significantly.  Although more labour intensive to produce and ensure appropriate nutrient composition it can be a very satisfying process and create a more closed loop system. The following is a list of some of the feed that can be easily sourced or cultivated for most omnivorous fish:

Meal worms
A plastic container is filled with a couple of inches of substrate (wheat bran/oat meal), a source of water (carrots, potato, etc) and mealworms (obtainable from many suppliers). It is kept warm and old dried or mouldy bits of vegetable are carefully removed. In a few months the worms have grown large enough start to pupate. Some of the pupae kept and hatched into beetles. These beetles are kept in another container with the same substrate and water source and in a couple of months they produce tiny worms. These can be fed to your fish. As long as you leave some mealworms to pupate and produce new beetles, your colony should be fairly stable.

Artemia/Brine Shrimp
As the name suggests, brine shrimp need seawater so firstly seawater must be made, using sea salt made up as at least 36 ppt, about 25ᴼC and pH 8 or 9. Aquaria are best suited to producing brine shrimp and the eggs can be bought from many suppliers. After stocking the eggs, they take about 2 days to hatch into larvae. Phytoplankton is particularly good for feeding the larvae. Larger larvae and adults can be fed with: yeast, wheat flour, egg yolk and/or soybean powder. The adult brine shrimp are an excellent food source, particularly for newly hatched/young fish as they are high in nutrients and move about- triggering the fishes reflexes to eat it.

Black soldier fly larvae
The larvae of the Black Soldier Fly are voracious consumers of decomposing waste such as manure, green waste and cooked and uncooked food waste – basically they eat anything and reduce the mass and nutrient content of that waste significantly.   The larvae are a high quality source of protein, have a short life cycle and mature larvae even migrate from the feeding ground effectively harvesting themselves making them an ideal supplemental feed or on-farm feed ingredient. The fly is a tropical species so production units must be insulated over winter. A product called the BioPod is specifically designed for BSF food composting and through clever design, has the added benefit of self-harvesting the larvae.

Find out more here…

Earthworms, bloodworms, and composting worms all make excellent fish food and plant off-cut digesters! The leachate from wormeries and worm teas also make an ideal disease suppressant and supplemental foliar feed for plants. It is worth noting that some fish can, like humans and and our pets, be fussy eaters sometimes and it can be hard to get fish to eat pellets after a “live” food diet, and visa versa.. but something well worth experimenting with.

In summary
We recommend that you consider any one, or a combination, of the feeds above as a supplement to a standard pellet fish feed.  Nutrition for living beings is a complex subject, especially in outside of their natural environment. Just as we wouldn’t feed our dogs or cats exclusively a single, or even a couple foodstuffs, please consider feeding your fish a varied diet that includes a reputable, in date, pelleted fish feed suitable for the fish species you are growing.
Hopefully you have also picked up on the message that what you feed your fish, ultimately then feed your plants, and then going a stage further the amount and quality of the protein in the fishes diet, will directly effect the amount of dissolved plant food (ammonia-nitrates) that is produced into the water.

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