Whats the difference between gobies and blennies? The store sold me a "blenny" but I'm 99% sure it's a goby.

Question

The reason I ask, is that this fish has dissapeared. I bought 2 blennies at the same time in hopes of reducing algae. My algae/sailfin blenny is awesome and eats like a shark. But after 2 days of hopping along the bottom, the other one is gone. Could he have buried himself out of sight? Jumped out of the tank? Been attacked by other peaceful tankmate? (I have 3 tomato clowns, one blue tang, and one valentini puffer.) I have not found him outside the tank, but I'm sure the cats would take care of him rather quickly. Please help! I'd hate to give away a $25 fish so easily.

Answer 1

I'll start with the difference first - it's easier to answer. The simplest way to tell the difference is to look at the fin on the back. A blenny will have a long, continuous fin, while gobies have a divided fin (it looks like two). There are other differences, but this is the easiest to pick out.

As far as what happened? It's really had to know. In general, it's not a good practice to mix fish of similar colors or body shapes - it reduces territorial aggression. Your existing blenny could have seen the new fish as a competitor, particularly if your tank is small. He might have been attacked by one of the other fish if they were a good bit larger and they saw him as a possible meal. He could have jumped (it's a good idea to keep a cover on the tank to prevent this, plus it cuts down water evaporation), or he could just be hiding well if you have a lot of live rock. If he's a gobie, many will construct tunnels under rocks. Be aware that any rockwork in your tank should be sitting on the floor of your tank, not on the gravel - otherwise any tunnelling could cause the rocks to shift and hit the glass.

If your tank isn't too large, you could try moving a few of the rocks around to see if he's in hiding. Otherwise, you'll have to wait to see if he reappears on his own. In the event that you would suspect a tank death, you should test your water in a few days to see if there will be an ammonia spike.

Answer 2

Blennies And Gobies

Answer 3

If you don't have a complete lid on the tank, Gobies will probably jump out.
Some gobies (shrimp gobies) will build a cave by digging in the sand under rocks, he may be hideing there.