What type of goldfish? There are many different varieties of goldfish, and they are loosely grouped into two categories: single tailed and fancy/double tailed. Single tailed goldfish include commons, comets & shubunkins and they are the standard ‘normal’ goldfish that have a streamlined body shape and a single tail fin. Fancy goldfish are pretty much everything else, including orandas, fantails, blackmoors, pearlscales, etc, and they generally have a rounder body shape and double tails. Single tails are faster, better swimmers than fancies and they also grow larger which is why the tank size recommendations are a bit different for the two groups. What size tank do they need? Goldfish are big fish. The tiny ones in the pet shop are babies that have the potential to grow to at least 8-12 inches long, which means they need big tanks and also big filters to cope with the waste from such chunky fish. Fancy goldfish need as a minimum 100L for the first fish and 40L for each subsequent fish, so at least 140L for a pair, though bigger is always better. Single tailed goldfish are really classed as pond fish and as such would ideally be kept in a pond. If kept in an aquarium the tank should be at least 4 foot long (preferably 5-6 foot), and you should allow for at least 100L per fish, though again bigger is better. While they are babies you can get away with a smaller tank in the short term, but be aware that they do grow quickly! The same goldfish at 2 months old and 12 months old: What kind of filter do they need? As goldfish are large fish that produce a large amount of waste, external filters are generally the best for them. The filter should be able to turn over the volume of the tank 6-10 times per hour. Which means that a 200L tank should have a filter that is rated 1200-2000L/H, the higher the better really. Don’t goldfish grow to the size of the tank? In a way this can be true but the real question then should be, is it healthy for the fish? In a small tank the waste produced by the goldfish will eventually overwhelm the filter and the water quality will become poor. In a small body of polluted water the goldfish will release a growth-inhibiting hormone, which will stunt their growth. However, evolutionarily speaking, this would have only been intended as a temporary fix for a fish that was stuck in a small area during the dry season. Kept permanently in such conditions will have a negative effect on the fish’s immune system and its overall health. A goldfish kept in a small tank with pristine, clean water will usually outgrow its tank. What do they eat? Goldfish are omnivores and are usually not fussy! Good quality sinking pellets are a great staple diet, as is gel food such as Repahsy. They will also enjoy algae wafers, vegetables (peas, spinach and courgette go down well in my tank!) and frozen foods such as bloodworm & brine shrimp. There’s more great info on the basics of fishkeeping here Goldfish don’t generally require a heater as they will do just great at room temperature, but an absolute must-buy is a good quality test kit. Goldfish make fantastic pets, they can be very personable, have great character, and given the right environment they can be with you for 10-20 years or more!