Fish remains have been used for fertilizer for thousands of years. As long as you bury them at least a foot deep where dogs and other mammals are not likely to dig them up, they will release nitrogen, phosphorus, calcium, and trace minerals to roots. While you're at it, throw in any other scraps you may have of vegetables, egg shells, banana peels, etc. This is the circle of life, and where all dirt comes from in the first place - decayed organic matter. Just don't use too many - one or two per plant is plenty. Spread the wealth around to all of your plants!