to get a:

silky shark
twin-fin spotanus?

I finally got a greenfin beta by breeding (kept buying the common eggs hoping to eventually get one and the still-needed above-mentioned...but so far I just keep getting fish I already have or don't need)

I have:

twin-fin shark
pink shark
spined shark
greenfin spotanus
pink stickfish
spined stickfish
spined beta
twinfin beta
silky beta
pink beta
greenfin beta
hornet fatfish
twinfin fatfish
golden goldbulb
wasp bananafish
twinfin fruitfish
orange fruitfish
silky fruitfish
golden goldshark

The twin-fin Spotanus can only be bred from two other Twin-fin Spotanus's or gotten from eggs.

You can't get a Silky Shark with those fish species, either.

A Silky Shark, like the Twin-Fin Spotanus, cannot be bred from any other species.

that figures lol (maybe change that in a future expansion) ended up using the time trick and got what I needed lol