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Stocking and Compatibility

by Dr. Adrian Lawler
Extracted from the staff Operational Handbook which Dr. Lawler wrote as Aquarium Supervisor for the J.L. Scott Marine Education Center and Aquarium, of Biloxi, MS
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After treatment (or quarantine), specimens are transported in a cleaned bucket containing untreated water of approximate salinity (FW or SW) to the display tank proposed, and introduced by pouring into the tank, transfer via net, or transfer via hand - making sure that the bucket, net, or hand does not go into the display tank.

The display tanks proposed for new specimens are chosen based on the following criteria:
-Correct section of Aquarium for display of that organism (e.g., an estuarine species would not go into an offshore tank). 
- Size: not too small to get eaten by those already in tank and not too large to eat those already in tank.
- Compatibility: whether the introduced specimen or present tank occupant will attack other specimens (nip tails, pick off scales, violent attacks, or cause other injury or stress). Compatibility can be dependent on tank size - as tank size increases (and habitat space) aggression can decrease.

Experience over the years has given us much information on compatibility, some being:
- Puffers nip many species, including other puffers, spiny box fish, hogchokers, flounder, seahorses, and other slower-moving animals.
- Pinfish fight each other and pick on smaller fish.
- Pigfish fight each other and sometimes pick on other species.
- Sheepshead fight each other and also pick on other species.
- Seahorses and pipefish cannot compete with more active fish for live food.
- Spadefish can pick on bottom fishes as stingrays, hogchokers, and flounders so much that they die.
- Unless a tank is large, two FW catfish in a tank will fight.
- Gags will kill another gag in the same tank and try to eat any new smaller introductions.
- Bullminnows will attack smaller fish and also pick on hogchokers and small flounders.
- Razorback musk turtles will chase and bite out sections from the rear part of shell of soft-shell turtles.
- Male tilapia should not be displayed after they become mature because they chase and kill other fish in the tank, and make nests (and thus holes) in the substrate.
- Cocoa damsels are highly territorial and will pick on most species you add to their tank.
- If two male snapping turtles are put into the same tank, the larger will usually pick on the smaller.

After the organisms are stocked out, each tank with new specimens should be examined immediately to make sure no aggressive behavior is evident. If fighting occurs, one must be prepared to move the newcomer to another tank. Tanks with newly introduced display animals should be closely observed for two to three days for any problems arising from the new introductions.