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[FishingDavid1990]

Hey guys. I have a 20 gallon tank with treated tap water. In it I have sailfin molly, least killifish, bluefin killifish, and Golden Topminnow. The last thing I wanted to add was a couple of Melanistic Gambusia. My plan was to add them last since I heard that they are aggressive. I wanted everything else to feel at home in the tank already, and for the Gambusia to be the newcomers. I thought that the Gambusia would be the most hardy fish of them all and would be really easy to introduce to the tank and get them eating and all that but they keep dying within an hour or so of being added to the tank. 

Everything else has been in the tank for almost three days now and get more and more comfortable every day. They have started getting used to movement outside of the tank and not darting to hide every time I walk by. They have all started eating. They havent been chasing or nipping at each other. Its been awesome! But the darn Gambusia wont stay alive. 

Ive gotten the mosquito fish from two separate locations. One location is a bigger creek with very clear water and lots of plants. That location required a drive home, and although all the fish I brought home with me were alive when I arrived one died shortly after being introduced to the tank and the other swam around strong, checking out its new home for about an hour. I thought that one was going to make it, but it eventually died. I am still very new to driving around with fish and so I assumed that they died from the transport. 

 

After that I ran out back to the ditch behind my house, which is muddy and shallow and gross, and got one from that ditch. It went straight from the ditch into a bag to acclimate to the temperature (which I did with all of them) and then was released into the tank. It swam around strong for about 20 minutes and then died. 

I was watching them pretty intently and did not see any of the other fish messing with any of them. I am just so confused. I really thought they were the toughest fish of all with how many of them are swimming around all over the place around here. 

I would just be like "Forget it, I do not need Mosquitofish" (and still might) but these are the one fish that my wife really wanted. I kept telling her "Ok, but they have to be the last thing to go into the tank" and now when I finally get some for her they keep dying. 

 

Any advice appreciated. Or if I should admit defeat that is fine too. I dont want to keep killing fish especially when everything else with this (my first) native tank has gone do smoothly. 

TLDR Notes - 

20 Gallon Fish tank

Standard Filter

Treated Tap Water

Substrate, plants, sunken logs, rocks etc all taken from local creeks

Fish taken from local creeks

Tank is only 5 days old. 

 

None of the other inhabitants seem to be picking on the Gambusia 

Please let me know if there is any additional info I can provide that might help. I can test my water as well if that might reveal something useful, even though I just did yesterday.

Thanks! 

 

 

[UncleWillie]

Strange indeed.  There are a few things to think about, and maybe we can narrow down the cause.

First, a five-day old tank is very new.  How many fish do you currently have in there? There could be an ammonia spike in a tank that new, depending on number of individuals you have in there.  Although this ammonia spike would likely harm you existing stock, not just the Gambusia.  Test the water chemistry and do partial water changes over several days if needed.  I know you tested the water yesterday, but what were the numbers?

 

Second, speaking of water chemistry, you mentioned that you float the bag of fish to acclimate the fish to the water temperature.  This is good.  Do you also acclimate them to the water chemistry as well?  I usually float fish until water temps are the same, then exchange about 1/4 of the volume of bag water with tank water and let the fish sit for another 10 or 15 mins.  I do this repeatedly until the bag water is nearly replaced with tank water.

 

Lastly, the transportation and handling.  How are you transporting the fish?  Coolers are a good way to move fish because there shouldn't be large temperature fluctuations.  Fish taking a long ride in a cooler in the cab of a car is a lot different than fish being in a dark-colored 5-gallon bucket sitting in the sun in the bed of a truck.  Temperature can fluctuate a lot from creek water, to bucket water siiting in the open air or sun, then into a hot (or cold) car, then inside of a house, etc. Also, consider added just a spoonful of salt to your transportation water.  Also, when transferring fish from water to bucket, bucket to cooler, cooler to bag, bag to tank, try to handle the fish as little as possible to reduce stress or damage.  I know these sound simple, but I'm just trying to cover all the bases.