Avoid Overfeeding


Feeding marine fish is very enjoyable, an interaction between the aquarist and his/her livestock. Some fish are usually easy to feed such as damsels and others could be more difficult such as some butterfly fish.

Feeding is so enjoyable that there is the danger that too much food will be given and this is very easily the case particularly for the beginner. Fish require sufficient suitable food to remain healthy and active as do all living things. It doesn’t take a lot of effort to tip the scales towards trouble though.

What trouble? To answer this requires another question – what happens to uneaten food? Excess food will sink into the reef and become inaccessible. There isn’t a ‘living reef’ in a fish only system but many of these systems have rocks installed. In a very mature system, particularly a reef aquarium, there could be many tiny organisms that could consume some of this food, but this cannot be relied upon. So this lost food rots and eventually produces nitrate, a definite undesirable. The guideline nitrate level for a reef system is 10ppm nitrate or less and for a fish only 30ppm or less, excellent if lower levels can be achieved. Overfeeding is likely to cause nitrate levels to go in the wrong direction. Nitrate levels are helped by weekly partial seawater changes but the amounts involved would need to be significantly increased if nitrate rises excessively. The problem with excessive nitrate is that it can cause corals to negatively react by not opening properly. It can also lead to that yukky, horrible encrusting and/or stringy and clogging nightmare called undesirable algae. Once undesirable algae has a foothold it can be difficult to eradicate though steps can be taken to do this – one of these being the reduction of nitrate.

‘Ah’, says the more experienced aquarist, ‘reef systems mostly, sometimes fish only, contain live rock and this can help with nitrate reduction’. That’s correct, some of the bacteria involved in the nitrogen cycle do utilise nitrate. With a strong presence of nitrate the numbers increase but there is a limit and this can be seen by the aquarists with live rock and elevated nitrate levels. The hardworking bacteria do a fine job but should not be overly relied upon. Why do systems using live rock get nitrate problems?

So overfeeding is abusing the system. Is it cruel? Well, it could be argued yes from the purely livestock point of view but in this case usually the answer is no. Why? The aquarist involved, very often inexperienced, is rightly concerned for the welfare of the fish, wanting to be sure they are adequately fed. It is the opposite of cruel, a good concern that the fish have enough food and are not stressed in this way.

The fish don’t help though. Go near the aquarium and some fish may rise and beg, cruising in the food area of the aquarium. Naturally the less experienced will wonder if they are hungry and could put some food in for them. Resist additional feeding.

Fish will usually grab available food to ensure they get it and not another even if they are not particularly hungry. They take advantage when the chance is available. They could grab some food and force it down. This could mean that some earlier food is expelled semi-digested to make room. Of course this will rot down and assist with the production of nitrate.

Fish should obviously be fed suitable food so they are likely to take it. Then it is the method of feeding that should be considered. Flake food for example should not be dumped on the seawater surface for the fish to get as it sinks. It could sink in too large an amount and much of it could reach the rocks or bottom. Some of it could go over a weir or be taken into piping and be lost and rot. Auto-feeders can cause trouble as they dump dry food on to the seawater surface.

A good way to feed (assuming the fish kept are not specialist feeders but the ‘easier’ fish the less experienced are likely to have and should have) is to use some small tweezers and a very small container. At feeding time put some high quality marine flakes in the container, not too many. Add some fresh water (or seawater from the aquarium if preferred), enough to cover the flakes, this soaks them so they will sink. With the tweezers, drop two or three flakes into the aquarium and watch the fish take them. The feeding area should be generally away from pump outlets and weirs. Provided the fish take them, continue to drop flakes in. Some fish will lose interest, or start to, before others. When they all seem to be losing interest stop feeding, even if there are flakes left in the container. Throw the excess away.

The above method does not solve the problem of fish overeating as described earlier. It does massively reduce the lost food though there are always one or two flakes that escape. Of course, flake should not be the only food fed – occasional brine shrimp etc will be enjoyed. The control of the food should be adhered to whatever the food type.

Before experience is gathered there could still be a concern about the fish having enough food. Quietly stay at the front of the aquarium and observe the fish. Each one will eventually present a head to tail view, that is down the length of the fish with the head foremost. The shape should be rounded and flow from head to tail, not thin.

After a short while the aquarist will learn the amount of food that is likely to be taken by the fish and will probably be surprised that the amount is quite a lot less than expected. If a fish by unlikely chance didn’t get enough at one feed then the fish will be fine until the next feed. Many fish find additional food in the aquarium, particularly a mature reef system.

Along with ongoing adequate maintenance which includes partial seawater changes, careful feeding will contribute immensely to the health and well-being of the livestock.