PlanetCatfish.com

from the website, m.castaneus is said to be found in river... but i caught mine, 38 of them from the beach.... i dont know it is really m.castaneus or not but it looks like it... and it stings.....

may i know how much food they eat and how often? because i feed them bloodworm and i have to put 7 cubes of the catfishes + some small sea crabs...... is that normal? i placed all the 38 catfish in a 2' aquarium with seawater taken from the beach also...

so.. any comments please?

I am guessing that you either have an estuarine Mystus or an ariid instead of M. castaneus, but their feeding habits are pretty similar in that they will eat as much as is given, so it's better to feed them sparingly.
You did not mentione the size of the fish, but I am guessing that they are pretty small at the moment, so the 7 cubes of bloodworms should be enough. They will most likely leave the crabs alone, so you should remove them from the aquarium.

i caught another 4 today so total is 42 now.. its around 2 inches long each....

but something bad happened just now... i turn off the air pump to c the fishes eat the worms... today i put 10 cubes of it.... then i fogot to turn the air pump back on.. and i went out... when i came back 4 hours later.... only 3 survived..... the other 39 is dead!!!