Unknown Fish?! Help Please!

[TDPUK]

Hello guys!
 
I'm classing this as an emergency for the simple fact I don't want to put any of my other fish at risk.
 
I recently purchased 2 Boesmani Rainbow's online and was sent these. I'm sure they've made a mistake. Can anyone tell me what species of fish this is please? I'm sure it's a Australian Rainbow. 
 

 
Thank you!

 

[Paradise3]

Firstly - It should not be in your tank. The only rainbows suitable for your tank(40l) are Dwarf Rainbow species like Forktailed, etc. These Rainbows are the bigger and more chunky species and need longer and bigger tanks than yours.
 
Secondly - They need groups of 6+. Not pairs. They are shoaling species and therefore need a shoal to be comfortable.
 
Thirdly - It looks like a Melanotaenia splendida to me. However, there are 5 different Melanotaenia splendida... All named for the different rivers they come from(I think...). Your's looks young and stressed, therefore I'm not sure which one it is.
 
 
Edit: Sorry if I sounded harsh there.... I didn't mean to.

 

[Chad]

I'm not a rainbow expert but it does look like a juvenile/female to me. I agree with the above about young and stressed. These two things make a big difference. Stress dulls the color, which is one thing that we often use to identify a fish. With age and sexual maturity fish will take on different morphology and often can't be well identified until they get older and obtain more of the mature characteristics.
 
I'm not sure what size tank you have so I can't comment on size suitability.

 

[Paradise3]

I'm not a rainbow expert but it does look like a juvenile/female to me. I agree with the above about young and stressed. These two things make a big difference. Stress dulls the color, which is one thing that we often use to identify a fish. With age and sexual maturity fish will take on different morphology and often can't be well identified until they get older and obtain more of the mature characteristics.
 
I'm not sure what size tank you have so I can't comment on size suitability.

 
I went through the OP's other posts not long before this was posted and these two Rainbows are in a 40l with Guppies, a Molly, a male Betta and an Angelfish(if that one didn't get re-homed already)