Live rock is simply any rock that has been in the water for at least 6 months. It has bacteria, sponges, seaweed, coral or any other life on it.
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Avoid Moorish idols, most butterfly fish and clown triggers.
The clown triggers grow to over a foot long and kill stuff.
Moorish idols are really hard to get feeding in captivity and 90% of them die within a month of being put in a tank.
Most butterfly fish are specialty feeders and eat small worms or corals. Some butterfly fish do well in aquariums if you get them at about 1 inch long. Racoon, threadfin, Klein's, and vagabond usually do well in captivity but make sure they have nice solid bodies and aren't sunken in around the upper body or head. Never buy adult butterfly fish and only get little ones between 1 & 2 inches long.
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Fire gobies are great little fish. There are 3 species and all do well in captivity. They live in small groups consisting of between 2-10 individuals. They make a home under a rock or coral and have fantastic colours.
The 3 species are Nemateleotris decora, helfrichi, & magnifica.
The decoras are red, purple and white.
The helfrichi is a pale blue and white. The images online show a pink fish, which appears to be a new species or a sub species of N. helrichi.
The magnifica is red, orange and white.
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Anemone fish (clown fish) should only be kept in pairs. Buy two little ones from a group and they should turn into a pair. Try to get one that is a bit bigger than the other, the bigger will become female and the smaller one will become a male. Female anemone fish are always bigger than males.
There are small species of anemone fish and big species. The small species like Amphiprion ocellaris & percula grow to about 2-3 inches. Some like Amphiprion polymnus and A. clarkii can reach 5-6 inches. Most of the other species fall somewhere in between these sizes and grow to 3-5 inches long.
All anemone fish are highly territorial towards other anemone fish and even some damsel fish. They are even more aggressive when defending eggs and big prs of A. clarkii and Premnas biaculeatus have been known to kill smaller fish in the tank when they are breeding.
A mature pr will breed every 2-4 weeks when they are happy. They lay about 300-500 eggs on a rock at the base of their anemone and guard the eggs from other anything that wants to eat them. The eggs hatch at night after about 7 days and the young can be reared up on green water and small species of rotifers.
Anemone fish will eat just about anything and do very well in aquariums. They don't need an anemone to live in but most people like watching the fish swimming about in the anemone. Some anemone fish will only use a certain species of anemone, whereas other fish will hang out in a variety of different anemones.
Anemones can do well in aquariums if the water is clean and there is lots of light. Under good conditions the anemone will grow to a certain size and then divide in two. One anemone will stay put and the other will wander off and find somewhere else to live.