Over the years l've just about tried every fish going,the best diet l've come up with is this,l buy fresh Scottish rainbow trout(Greg will like that bit)then l cut up the whole fish from just behind the head making cutlets all the way down the fish,then cut the cutlets in half at the spine so each strip of fish contains bone skin and fins,then depending on the snakes l'm feeding l feed the strips or if needed l can cut them to whatever size l need,If l need to l then put the fish on a plate and freeze, so that l can just take the frozen fish strips as needed.
This is the controversial bit,l use socked fish pellets(where the protein is fish)very small pellets for neonate babys moving up to larger pellets as they grow,and for adult snakes l use a complete dog kibble,again well socked in fish water.
l started to do this with the problem of finding fish small enough for the neonates,with fish cut up not having enough nutritional value l found the vitamin and mineral content in some fish pellets very good for garters and water snakes.
l get very good growth rates and its a good adult breeding and maintainace diet.