Hello everyone. A few months ago I decided to create a pond for wildlife observation which had some great results. There’s a lot of animals that go there daily to have a drink and bathe, or even to live there. In the thread I created I talked about introducing Argentine Pearlfish (Austrolebias bellottii) since they are present in the area but people argued against it, saying that they might eat everything in sight and minimize biodiversity.
So the pond went on to be naturally filled with tadpoles, water beetles and plenty of other animals, except for fish. It is currently the middle of summer here and we had been experiencing heavy drought until a few days ago when there was intense rain, which naturally filled up the pond (I had been adding non-chlorinated water to it to keep it from drying out cause of the hot weather).
Yesterday when I went to check it out I noticed that there were some strange looking “tadpoles”, very small and weird. I then spotted some similar looking animals but bigger, so I got my net and tried to get a few. Lo and behold, what I managed to caught where crearly some type of fish. I was very confused as to how they got there, since there isn’t any natural body of water connecting the pond to nearby ditches or puddles, and plus those were all dried out from the drought. So how did this fish manage to get here? I didn’t put them there and neither did my family. So, thinking they were probably the same species of fish that I had seen in nearby ditches but wanting to be sure I took some pictures and uploaded them to iNat. They have since been identified as West Mosquitofish (Gambusia affinis) which are an invasive species originally introduced to Argentina around 1945 to control mosquito larvae population.
Doing some research I found a paper which studied Mosquitofish’s diet in the argentine province of Salta (im in Buenos Aires province) and it seems to indicate that they feed mostly on plants and occasionally on insect larvae. Even if they seem to be a naturalised species here, it seems that in other places like Spain they out-compete native fish species and can cause a lot of ecological damage. They are also on the 100 most invasive species list by the IUCN. Overall there seems to be a lack of information on their actual ecological impact in my area.
So here I have a big dilemma. Should I drain the pond in order to kill off all the mosquitofish and likely kill a lot of native species in the process (I will try to save and reintroduce as many tadpoles and water beetles as I can, but there’s gonna be casualties regardless) or allow the mosquitofish to exist here and have them potentially spread on further? If I am to take action it should be now that it is summer season, so I would let the pond dry out on its own and save the natives once the water level is low enough.