Fish food is what drives an aquaponics system.

Transcription

1 Feeding Your Fish Understanding the full effect of feeding fish in an aquaponics system is central to realising its productive potential. In this section, we look at some of the more important aspects of feeding fish. Fish Food - Fuel for Fish and Plants Fish food is what drives an aquaponics system. Not only does fish food provide for the growth of your fish, but the waste that they generate (coupled with uneaten food) is what eventually feeds your plants. In the wild, fish manage their own nutrition but in an aquaponics system they are entirely dependent on you to ensure that their nutritional needs are met. It is important, therefore, that you feed a balanced ration - and the easiest way to do that is to purchase pellets that are formulated for your preferred species - from a reputable supplier. Feed Conversion The capacity of a fish species to convert fish food to fish biomass (meat) is known as the feed conversion ratio (FCR). Fish usually have a low feed conversion ratio (1.5:1-1.8:1) when compared to most other farmed animals and birds. Meat chickens, for example, will have an FCR of around 3:1 and pigs may be upwards of 5:1. While it's important that you maximize your use of fish food, don't be too concerned if you don't realise the same FCR as a commercial producer...they will likely have invested heavily to achieve the sort of performance that they do. Your FCR will be like most other aspects of aquaponics - something of a compromise. Feed Composition Commercial fish pellets will generally comprise protein, carbohydrates, fats, vitamins, minerals and a variety of other ingredients including preservatives, binding agents and colouring. Proteins sources include fish meal, meat meal (and other abattoir wastes), dairy products, soybean meal, lucerne meal and various grains. The protein component of a ration provides energy and amino acids. Carbohydrates are included in the ration to provide energy. Fats also provide energy and fatty acids (essential for growth and development). Vitamins in the diet contribute to growth and the general health and well- being of the fish.

2 2 While most of the minerals are already available in water, traces will be included in fish rations to offset the possibility of vitamin deficiencies and disease. If you want your fish to achieve the optimum rate of growth, you will feed them a pelletised ration that has been formulated for that particular species. Fishmeal and Sustainability Since most of the fishmeal used in aquaculture rations comes from other fish caught for the purpose, the issue of declining fish stocks is a legitimate concern. The good new is that the aquaculture industry has dramatically reduced its proportionate consumption of fish meal and oil. While the dramatic growth of the aquaculture industry has meant that the overall volume of fishmeal has not declined, this has been offset to some some measure by a move to krill (tiny marine creatures) as one of the major sources of fish meal. Research into soy and grain- based rations is also ongoing. How Much? The amount of food that your fish will consume is driven by several factors including: Management strategy Feed pellet type and size Size (age) and species of fish Water temperature and quality Weather You should also understand that how much food your fish will eat is not necessarily the same amount that you should give them. In some situations, certain species will eat more than is good for them. Jade perch, for example, will eat more than their metabolism can sustain in colder weather. These fish are native to Australia's tropical zones. When they are kept in cooler sub- tropical environments, their metabolism will slow but they often retain an intense interest in food. This can prove fatal. Various authors propose feeding between 1.5% and 3% of the total weight of fish per day as a guide. Feeding at this rate assumes that everything is in good order. It also assumes that your fish are healthy and that your fish tank is at the optimum temperature. It also assumes that your bio- filtration systems are functioning perfectly. Feeding by weight requires that you catch a few fish (about six will do) and weigh them so that you can determine the average weight of a fish. Then you multiply that weight by the number of fish in the tank. For example, if you catch six fish and they weigh a total of 900 grams, then the average weight is 150 grams. Let's assume that you have 100 fish in the tank. That means that you will have about 15,000 grams - or 15kg. Feeding at the rate of 1% means that you would feed 150g - at 2% it would be 300g and at

3 3 3% it would be 450g. Note: The amounts that I have calculated are those that you would provide each day - not each feed. The total daily amount of feed should be divided up and fed out several times throughout the day. Now, while our fish might be able to handle that amount of food, the more important question is "Can your system process the amount of waste that that amount of food will generate?" If you're not sure of the answer, proceed cautiously (doing water tests as you go) until you establish what your system is capable of - and then apply a generous margin for error. Since I'm not around all day every day, I have to be content with feeding twice daily. I feed as much as my fish will take readily in a short time. That way, if they lose their appetite for any reason, I'll get to know about it very quickly. I can then adjust the amount of food while I investigate the problem. I always commence any such investigation with a battery of water tests. If you continue to feed when your fish have no appetite, the uneaten food will foul the water and create loading difficulties for your bio- filters. Eventually, the uneaten food will lead to the depletion of oxygen levels and will encourage the proliferation of heterotrophic bacteria, which is what you don't want to happen. It s often difficult for people to get used to the idea of withholding feed - we are so heavily wired into overfeeding everything (including ourselves). Assuming that the food is matched to the species, the worst that will happen if your fish get a bit less food than they otherwise might have had, is that they ll take longer to grow out. If you see food accumulating on the bottom of your fish tank, you should remove it and adjust the feeding rate. Withholding feed for a day every now and then will do more good than harm. If your system has to run unattended for hours, you may want to consider an automatic fish feeder. These devices dispense measure quantities of food at predetermined intervals. It should be noted that they are no substitute for regular supervision of the system because, if the fish go off their feed for any reason, the feeder will still keep putting the food in. For this reason, fish feeders are probably best used in conjunction with fish tanks that have bottom centre drains or other effective solids pickup features. At least that way, uneaten food will be removed from the fish tank. Weaning Freshwater Fish The fingerlings of some fish species may not readily take to pelletised fish food. I've experienced this with sleepy cod and golden perch. If you have this problem, you can try using the frozen bloodworms that are sold through aquarium shops. Once your fingerlings show interest in the bloodworms start to introduce some small sinking fish

4 4 food. Over time, reduce the bloodworms and increase the fish food. Storing Fish Food Like most commercial rations, pelletised fish food will deteriorate over time. The most serious issue with stale fish food is the loss of Vitamin C. To ensure that your fish food is kept in the best possible condition, I suggest the following: Purchase the minimum amount of feed that is practicable. If necessary, share feed purchases with one or more fellow Aquaponicists to ensure that you are always using fresh stock. If you have to buy a larger quantity than you really need, it is a good idea to bag it up into 1kg lots. Seal the bags - ideally make them airtight. Store all feed in a cool, dark and dry place. Small quantities of food can be frozen to maintain optimum quality. Other Useful Tips Make sure you buy your fish food from a supplier who is turning their stock over quickly. Fish food deteriorates much faster than other livestock diets. Feeding cheap food is false economy - stick with the recommended protein level for your species. Feed the largest pellet that your fish will readily eat. It's good for the fish - and for water quality in the fish tank. Small fish will (proportionately speaking) eat more than larger fish. DIY Fish Food Sooner or later, most aquaponicists think about producing their own fish food. One issue with proprietary rations is that the manufacturers will not usually divulge the contents. Pelletised rations may contain chemicals of some type or the other - even if just colouring agents and binders. Some are motivated by concerns about sustainability while others aspire to greater self- sufficiency or wish to save money. I understand (and share) the desire to become self- sufficient in the production of small livestock rations, so, while I feed pellets, I continue to experiment with supplementary rations. If you're thinking along a similar line, the first thing you'll need to understand is that it will almost certainly take longer to grow your fish if you do not feed a pelletised ration design specifically for fish. The next thing to understand is that it isn't as simple as it appears to come up with a suitable ration because, while most livestock rations comprise a mix of protein (animal and/or plant), carbohydrates, fats, vitamins and minerals, it's the precise mix of these things that separates the livestock nutritionist from the rest of us.

5 5 Having said that, there are no nutritionists to be found in the natural world from which our fish originate and yet they seem to manage. Home- grown Food Options Some people approach the DIY fish food thing by attempting to make their own fish pellets. I ve seen all manner of concoctions proposed for use as fish food and I ve even tried some of them myself. All I ve achieved, so far, is to get myself banned from the kitchen. Even when the fish ate them, my concoctions discoloured the tank water and boosted the ammonia levels. Another approach is to acknowledge that, in the wild, fish are opportunistic feeders - they'll grab an insect or a seed...or nibble on a plant...or each other. Basically, they're just picking up a bit of this and that as it comes to hand (or mouth). My latest approach is to try to reconcile opportunistic feeding with the knowledge that commercial fish diets comprise protein, carbohydrates, fats, vitamins and minerals. I believe (but have yet to confirm) that it may be possible to feed an animal protein source (like worms, fly larvae, mealworms, silkworms or feeder roaches), followed by some carbohydrates (like softened rice or sprouted seeds or grains). The third course would be duckweed. My rationale for this regime is that the protein is usually the most expensive to provide so I want that eaten first. The grain or seeds is the next most expensive so I want the fish to eat it while they are still hungry. The duckweed is the least expensive and, even if they are no longer hungry, the fish can graze on it at their leisure. Since it will float on the surface of the tank until the fish decide to eat it, it will not impact water quality. This dietary regime is for omnivores so it may not appeal to all species. Certain species will eat some things and not others. For example, my jade perch have always eaten duckweed while other aquaponicists report that their jade perch won't touch it. I give duckweed to my fish as soon as they are big enough to fit it in their mouths. Fish, like other farmed creatures, sometimes need to be trained to eat certain things. Previous editions of this manual contained a section on Black soldier fly larvae. These incredible creatures are able to play a number of important roles in any urban farming situation. We started to feed them to our fish (and the fish liked them) but we discovered that the tough outer skin of the larvae was largely indigestible and added considerably to the volume of solids in our systems. While this would be less of an issue in larger, lightly stocked aquaponics systems, it became a problem in our small, heavily stocked systems. These days, we still grow BSF larvae but we no longer regularly feed them to our fish...and our chickens love us for it. Free Range Fish Food

6 6 Fish are often partial to a range of bugs including slaters and earwigs. They also like snails - crush the shell to expose the snail meat and throw it into the tank. Another idea that has merit is to suspend a low wattage light over the fish tank. During the summer months, this will result in a bountiful harvest of flying insects - often a welcome addition to the fish normal ration. Summary If you want to grow your fish in the shortest possible time, my advice is to feed them a pelletised ration formulated especially for your fish species...and get it from a reputable supplier who is turning their stocks over frequently. Having said all of that, producing your own small livestock rations isn't just a matter of economics; it s a cornerstone of any attempt to produce clean, fresh food. We are educated to believe that something that costs little or nothing is of questionable worth but the notion that you can t get something for nothing is a commercial one. Nature (and integrated backyard farming) operates on a different premise where everything has value. - o0o-