The aquarist could own a fish only or reef aquarium, whichever it is there is one action that is very low in popularity – catching a fish.
The natural reaction of a fish when anything seemingly threatening approaches is to move away and hide. This is the survival instinct from the wild. It is the same reaction as hiding when night time approaches. Failure to get out of harm’s way and hide could mean death.
In the aquarium the fish have their wild instincts. These do become modified to an extent, for example when the aquarist approaches the aquarium the fish could come to the front in anticipation of food. Overall though there isn’t much change, generally introduce a new fish and the resident fish usually back off until they are confident of safety in the new fish’s presence. Likewise, if the aquarist puts a net in the aquarium the fish will move away rapidly as it is an unknown presence.
If all is well there may never be a need to catch a fish. If the aquarist goes through the correct careful sequence with purchasing and introduction there could never be any sickness, and similarly if fish are only bought when it is known they are compatible with the other fish and/or reef there should not be any excessive aggression or undesirable actions such as eating corals.
There may be a time though when a fish is bullied or just off colour or clearly sick. Something needs to be done to assist the fish and also in the case of sickness to protect the other fish.
This is a problem in itself as catching a fish is very stressful to the fish (and also to the aquarist!). This stress will not help the fish’s condition at all and so catching needs to be as efficient as possible.
The first action is observation. Does the fish usually hang about in one particular area, hopefully high in the seawater column? Second, does the fish need to be caught immediately or could a day or two pass? These questions decide the first attempted method. The aquarium décor is not upset with this method, which relies on the fish gaining confidence in the presence of a net. Put a suitably sized net in the aquarium (ensure it is seawater safe) and make sure it remains in the chosen position. The handle must be easily reached without alarming the fish. The net position should be well beneath the surface in an area where the fish is likely to swim. After a time, sometimes hours, sometimes days, the fish will lose much of its fear of the net and swim above it. This is what is needed, the fish to swim over the net. The best time could be during feeding if the fish takes food. The aquarist is in position and when the fish is above the net, the net is moved up at speed giving the fish no time to escape. It needs first time success really or the fish could once again fear the net.
If the method above is not of use then procedure could depend on the type of system. If the system is fish only with few rocks and filtered by say a canister filter, there isn’t any problem in moving the rocks, or most of them, temporarily out of the aquarium. Getting the rocks out of the way will make catching the fish much easier as the fish will normally choose the rocks to hide in. There could be desirable growth on the rocks and so the aquarist should be prepared to keep them damp with seawater if they are not placed in a bucket. Moving the rocks could also throw up a considerable amount of detritus, so once the action is over the detritus can be removed before the rocks are put back. The rock removal action will cause stress to all fish, not just the one being caught, as their safe homes will suddenly disappear. Preferably two nets should be used as one will chase the fish and the other will block the escape – either net could catch the fish.
If the aquarium has a lot of live rock, which could be fish only but particularly a reef system, then removing the rocks is not usually an option. However, the possibility should be considered. With rocks in the aquarium it will be very nearly impossible to catch a fish as it will simply dive into them. So another method has to be considered and this is the fish trap.
Fish traps are available commercially and usually consist of an acrylic box with a vertically sliding door at one end. They are designed so that they fill with seawater and sink though sometimes a small pebble or two assists this. Into the trap goes food, the aquarist will know the type of food the fish likes best and, if practical, this should be used. Using a trap is likely to be successful several times! It could be that the first caught is a shrimp, then later a fish but the wrong one, then another again the wrong one. In addition of course the fish need time to get used to the trap, at first it is an alien presence. Eventually the target fish should be caught.
There is another method but this one requires a difficult decision. If one fish needs to be caught and this is an immediate requirement the aquarist must consider taking down the aquascaping or reef. As already said the fish isn’t going to be caught with a sizeable rock structure present. Deciding to take down the aquascape/reef is not easy, especially with an aged aquarium as it will have developed a great deal. We aquarists must always consider the welfare of the livestock and balance the damage we may do with an action to catch and maybe save one fish opposed to the troubles that could be caused to numerous corals, shrimps, crabs and other fish. Sometimes it could be best to leave the problem to Mother Nature and see what happens*. It is not unknown for an ‘ailing’ fish to recover especially if the habitat is of high quality. If ‘leaving’ is the decision then the fish must be monitored. Has it been seen, how is it doing? If the fish fails to appear one day and remains unseen it is probable that it has died within the rockwork. Bacteria and maybe shrimps clear away a dead fish rapidly. However, seawater quality must be tested more often than usual, that is ammonia and nitrite, until the aquarist is confident there isn’t a problem.
*‘Leaving’ is not an option when an ailment that requires immediate attention has been identified. Proper medication needs to be administered without undue delay. Again this is easier in a basic canister filtered fish only system than in the others. Medication will not be covered here.
So as said catching a fish requires that basic aquarist’s attribute patience, and sometimes a lot of it. It can be done though, and being successful rests considerably on the catching method chosen.