Thaliak Caimans are your best bet for seaborne and the go-to seaborne generator for most people. The other fish aren't worth the trouble for the low rates they return seaborne (like 6% chance). It's Middle Thaliak River from 3pm-6pm, any weather, Almost a guaranteed mooch from Bullfrog, which is a very common bite from bladed steel jig, or a less common mooch from sweetfish. It's a very easy fish to catch 3-4 of in the timeframe every time around, with a 40-50% reduction rate to seaborne at 7/8 and 8/8 as well as a very high HQ sand rate as well as a chance at 1-3 sands. Back when I was making full i170 crafting sets for myself, I'd usually get multiple seabornes every time around and seaborne was the easiest for me to get by far.