This is a nemipterid fish, possibly Scolopsis affinis Peters 1877.

Hi Glen,

I have done a bit of work with juvenile Lethrinids  on video from the Pilbara and they are notoriously difficult to identify at this size. They do not look like our L. nebulosus as the head is too flat and there is not enough blue around the eyes. The spot on the first image makes me think L variegattus as the adults sometime get this whilst feeding.

L. genivittatus can also get this spot AND we regularly see juveniles with the yellow cap as you have in the second picture.

May I ask which bay? 

I recently had a student in our lab working on tropicalisation of fish at Rottnest and he found some interesting species. Only adult L. nebulosus though. Another recent student  focused on juvenile Lethrinids in the Pilbara and spent months trying to identify difference in patterns, behaviour and habitats. She will be published soon.

I have only seen L. nebulosus and L. miniatus at Rottnest. Even then only adults. These images are very interesting. 

I have posted a link to some footage we collected at Ningaloo. You may recognise you species in the mix. There was five species of juvenile Lethrinids in this footage.

Thanks,

Todd. 

https://www.facebook.com/marineecologygroupUWA/videos/761614707318485/

Hi Todd

Thanks for your reply - much appreciated. I found these fish under our mooring in Thompson Bay, not too far off the Hotel Jetty. We have seen what we believe to be juvenile L. nebulosus at a number of sites around Rotto this last summer - and plenty of adults. Having research these ones at length I am quite convinced the little one is L. genivittatus as it is the only juvenile Lethrinid that has a pointed tip to the shoulder blotch which crosses the lateral line. The other diagnostic feature is the extra long second dorsal spine. Not sure about the others, but I am hoping they will hang around long enough for me to observe them getting older.

If you happen to have any pics of cryptic/unexpected fish at Rotto I'd love to see them. We are printing some verifiable pictures from the public in our book, which should be complete within a couple of months.

Cheers

Glen