disappearing or dying fish

[Denver]

I have a problem with fish disappearing or dying suddenly, only to find the dead ones being eaten by my sallylightfoot crabs. They have suddenly became aggressive, they are constantly trying to ambush my fish by jumping off my LRand trying to catch the fish and actually grabbing them in mid flight. Is this unusual or are these crabs just acting normal.
They are being fed very well. Please help

 

[jhnrb]

A Crab Is A Crab Is A Crab Is A Crab

Percnon Gibbesi (Sally Lightfoot Crab)

-Size- to about 4 inches

-Range- Caribbean, Indo-Pacific

-Minimum Aquarium Size- 50 gal. or larger.

-Lighting- Immaterial

-Foods and Feeding- Small ones are somewhat herbivorous; larger specimens are distinctly predatory. Will scavenge if appropriate prey are not present in the tank.

-Aquarium Suitability/Reef Aquarium Compatibility; Not reef safe. Large specimens get aggressive, predatory, and destructive.

-Captive Care; This speedy, flattened spider crab has a small body, long legs, and an endearing common name. A better name for it might be "Jekyll and Hyde crab" - it will seem to be a benign aquarium inhabitant for several months and then will undergo a personality shift, probably due to sexual maturity. The male claws enlarge and their bases swell to accomodate the larger muscle mass. The crab lunges at and often catches fishes. Large ones will tear apart sea anemones and corals to get their gut contents, and they will feast on small hermit crabs. These crabs are very fast and nearly impossible to catch, except in baited traps.

My advice is to get rid of um. hope this helps.