Reminds me of this book I think the fish are based on real species, but exaggerated.
On a hunch, I took a look at Cardinalfish larva and found a picture that looks REALLY similar to me. Be aware that I am NOT familiar with larval development in the least so I don't know if this early feeding phase is specific to cardinalfish or if it's very similar across a wide range of taxonomic groups.
My guess would be a Boston / Atlantic mackerel.
Just has some color variation.
If you run an image search you'll find some bostons that look enough like this.
This one in particular looks close to me.
A friend told me they look like some sort of minnows to them.