[oilinki (OP)]

I have a 1000 litre, free standing water tank where I collect tropical rain water for my home usage.
This is normal 1000 litre water tank, which is located next to my home. The only way for water to get in is from my home's roof through a 1mm sieve. I emptied the tank 6 months ago.

I live on a hill, about 100 meters from the sea shore and about 200 meters from nearest fresh water sources.

I live alone, surrounded by jungle and there is very little chance, any other person would have had access to my water tank.

The fish: So far I have seen 2 of them. Both about 4cm in length and with full fish appearance. I'll try to take a photo the next time I see one.

Now I have small fish living in my water tank and I wish to find out logical solution, how it is physically possible. I assume that these are freshwater fish as they survive the rain water conditions.

I talked about this issue with my friends on Twitter (TNS also participated), but I have not found out the answer. https://twitter.com/oilinki/status/1036528728208109569 [nofollow]

So far there has been several ideas

- Some fish species are able crawl on land
- Fertilised fish eggs inside of grown fish, which was catched and dropped by a bird
- Fertilised fish eggs caught to the feathers of a bird (kingfisher) and later dropped to my roof
- Waterspouts lifting fertilised eggs from lake or river, which ended up on my roof

I live in Phuket, Thailand and in this area we have a lot of Kingfishers. Darn pretty birds I wish to add.

So far the theory of fertilised fish eggs being caught by kingfisher's feathers, is my leading theory.

What do you say?

On the larger scope, this might also explain how fish populations were able to expand to upriver lakes, without trout like ability to swim upwards fast flowing rivers.

Please help me to figure out this mystery.

Ps. Are there fish, which carry their fertilised eggs inside or next to their bodies, instead of dumbing the eggs to the wild?

[wolfekeeper]

Maybe a king fisher caught a live fish, and was carrying it to it's chicks, and then accidentally dropped it.

[chris]

Maybe a king fisher caught a live fish, and was carrying it to it's chicks, and then accidentally dropped it.

Interesting theory - I don't think anyone suggested that one on the Twitter conversation about this...

[alancalverd]

The presence of identical freshwater fish species in different rivers has always intrigued me.The simplest model of an island(such as Great Britain) is a pyramid with a dry apex and water runing down the sides. The rivers are not connected at the watershed, and the salt sea at the base prevents freshwater fish from migrating between rivers at their mouths. But somewhere in the middle of the stream you will find the same native species (pike, perch, roach)  in each river, supported and  predated by pretty much the same ecosystem The probability of identical evolution of the top species in isolated biomes is negligible,and fish can neither fly nor walk across the land.

The least unlikely solution I have been offered is accidental transfer of pregnant fish or eggs, by birds, and I guess that might account for fish in  a tropical water tank.

[oilinki (OP)]

Are there fish species which carry fertilised eggs inside or outside of their bodies? I'm in impression that fish fertilise their eggs only in the water.

Dropping a fish in that case could be the answer.

Going further, are there fish eggs, which can survive birds or other animals ingestive systems? I'm wondering about similar evolutionary steps what seeds have gone through.

After all, that would be a great way to spread the fish to uphill lakes.

[oilinki (OP)]

Maybe a king fisher caught a live fish, and was carrying it to it's chicks, and then accidentally dropped it.

Adult size life fish would not be able to go through the 1-2mm mesh, which protects leaves to enter the water tank. Anything going inside must be small.

The water tank has another opening as well, but it's also protected by a mesh.

This was the second fish I had inside the tank. Actually the second fish got caught on 2mm tube which is coming from the tank.

I haven't checked what's inside of the tank for a while. I think I should do just that.

For me it's perfectly normal if there are tree frogs, snails, geckos or even snakes.. but fish is a whole different possibility.

[oilinki (OP)]

This is the water tank in question.

p1100898.jpg (134.01 kB . 439x780 - viewed 3728 times)

[wolfekeeper]

The presence of identical freshwater fish species in different rivers has always intrigued me.The simplest model of an island(such as Great Britain) is a pyramid with a dry apex and water runing down the sides. The rivers are not connected at the watershed, and the salt sea at the base prevents freshwater fish from migrating between rivers at their mouths. But somewhere in the middle of the stream you will find the same native species (pike, perch, roach)  in each river, supported and  predated by pretty much the same ecosystem The probability of identical evolution of the top species in isolated biomes is negligible,and fish can neither fly nor walk across the land.

The least unlikely solution I have been offered is accidental transfer of pregnant fish or eggs, by birds, and I guess that might account for fish in  a tropical water tank.

Not all that long ago, a few tens of thousands of years, Great Britain used to be connected to the mainland of Europe, because the sea level was a lot lower due to massive glaciation. Lots of rivers that now individually lead to the sea used to join up before proceeding to the sea in what are now the English and Bristol channels, and also, the glaciers themselves did wacky things, like damming up stuff and changing the topography by grinding grooves in the land, and when they melted, huge freshwater flooding happened that could easily push fish around.