Fresh/brackish Water Moray

[Lyle]

i have a 55 gallon brackish water tank with a specific gravity of about 1.005. my eel (Gymnothorax polyuranodon) was swimmin at the top of the tank today and looked as if he was gasping for air (kinda looked like he had swallowed a rock). hes been doing great for the couple months that i've had him, and the only things out of the ordinary right now are that i put him in my tank when it was freshwater and have slowly been adding the salt over the past several weeks (maybe hes not used to the salt even though hes a brackish water fish??) and alot of green algea has accumulated in the past 2 days because of a new lighting system and i have not had a chance to get a diatom filter yet (but green algea isn't bad for the fish, right??). so is he sick?? reaction with the salt? retarded?? help me! i really like this fish and don't want him to die!!

 

[andywg]

Have you been adding salt to the tank water directly, or raising the salinity through water changes? The former can cause problems as undissolved marine salt is pretty nasty for an animal to come into contact with.

Do you have any readings for ammonia, nitrite and nitrate? It may be that there has been a spike. G. poluranadon is said ot inhabit freshwater, but I would expect it to be able to handle low end brackish as well, considering the family it belongs to, so I would not immediately think of the salt as the problem.

However, it may be that the salt is the problem. If you have another tank you could always try and acclimate the eel over a couple of hours back to FW and see if it performs better.

 

[nmonks]

Brackish water fish can adapt from freshwater to brackish or marine conditions within hours, sometimes instantly. So it's unlikely the fish is "failing" in some way.

Raising the salinity above 1.005 is going to kill the freshwater filter bacteria, or at least suppress their performance until the brackish water bacteria have come online. If you're going to raise the salinity with the fish in the tank, it has to be done very slowly, with constant checks of the nitrate level. If you took 6 months to go from 1.005 to 1.010 that would do the fish NO HARM at all, and would leave ample time for the bacteria to adapt. This isn't the ideal way to do things, but it does work, and I've done this many times.

The trick is to add slightly more saline water with each water change (e.g. 1.005 to 1.006), and then do a nitrite test the next day. If there's any sign of nitrite, don't raise the salinity further, and make sure you perform frequent water changes keeping the salinity steady. Add extra aeration if possible, and cut back on the food. Basically treat the tank as if it was halfway through being cycled. Raise the salinity a little bit more after 2-3 weeks. Keep testing the nitrite, and keep doing water changes if things aren't 100% perfect.

By the time you get to 1.010 the bacteria will be almost entirely brackish/marine ones and you can usually fluctuate the salinity more rapidly, if you need to. 1.010 to 1.012, for example, seems to be completely safe.

Algae is harmless, and in fact the fish like it. A diatom filter is almost totally pointless in this sort of aquarium. It does nothing for water quality (ammonium and nitrite, anyway). A UV filter might cut back on algae a bit, but a skimmer would be a much better (and less expensive) investment.

Cheers,

Neale

 

[Lyle]

hey thanks everyone for the advice. the eel died unfortunatly... but at least i know why. i guess what happened was the nitrates went way up when the freshwater bacteria was dissapearing, and when the algae bloom came i turned the lights out, which i guess didn't help with the nitrates.....

thanks again
-lyle