Choosing Your Stock
SizeFish vary a great deal in their eventual size, and this will need to be matched to the size of your tank and your other fish. For fish that grow up to 20cm, you will need at least 8-10 times the fish's length as a minimum tank size. A fish that reaches 5cm will need a tank length of 40-50cm (1-2 foot), one that reaches 10cm will need a tank length of 80-100cm (3 foot) and one which reaches up to 20cm will need a 160-200cm tank (5-7 foot) The common phrase of 'only growing to the size of tank' is a misconception and you should consider a fish's maximum size as the size it will grow to. You should also consider the active nature of the fish – active fish will need more swimming space and large fish which are best kept in groups will need even more room.
Behaviour and compatibilityLike any other type of fish, marine fish vary a great deal in personality and behaviour – don't assume that because your retailer sells a fish it is safe to mix with all marines – a retailer may have many types of marine customer, with all sorts of tank setups, and any fish they sell may only be suited to a particular style of tank. Check for aggressive natures and unwanted attributes, some marine fish may kill or eat inverts or corals, others may disrupt the tank by moving rocks or sand, some are predatory and may eat other fish. You will also need to check that any fish you buy are compatible with the fish you already have or plan to get in the future. The best way to do this is to keep a list of your stock and planned future purchases – whenever you buy new stock you can show your retailer the list and check for compatibility, if there is a problem you can take the fish back since your retailer will be partly to blame from having checked your list.
Care requirementsSome fish may have special care requirements and you need to think about whether you can provide these or not. One of the most common with marine fish is extra feeding needs, and many fish may need several feeds a day and several different types of food. Other requirements might be a particular substrate, rockwork, or the fish may need to be kept in groups.