Well it's a species name not a genus name and ---pinna is "fin."
But yes, we are pretty stumped.
...Not satisfied, I went to Baensch and now I wonder if you're seeing Lemon Tetras, Hyphessobrycon pulchripinnis. The yellow is strongest on the anal fin. The eye is definitely red.
When they're more settled their body color will warm to a rosy silver.
Did I get it? Do I win a herring? ark ark ark ark clap clap clap