What type of fish? Are they in their own seperate aquarium? Is it heated? What are you feeding them?

sometimes water quality is key. Also size of tank. They may be babies, but you can't keep them in too small of a container.

I only had 4 babbyies now I have 1 he is by his self in a 10 gallent tank yes heated and crshed up fish flakes he is a sword tail

Batboy......check your water conditions. Do ammonia and pH tests to see how your water is doing.

Baby fish do not grow fast. If you can get a culture of micro worms and hatch some baby brineshrimp....and still feed crushed flakes.......you may find that your swordtail will grow faster. When feeding foods like brineshrimp and micro worms......you must do more water changes though as they will pollute the water quickly.

I think the main thing to be concerned about here is that you had 4 baby fish and now you only have 1. You should try to find out the problem that caused the loss of 3 fish.

The good news is....that your adult female swordtail will probably have more babies in about a month. If you provide lots of hiding spots and floating plants....real or plastic....more baby fish will survive.....as without cover the adultfish will eat them.

A low flow filter is helpful. Usually fry tanks utilize an inexpensive airstone driven sponge filter. But anything low flow will do. Brine shrimp kits are relatively inexpensive and easy to do, you can set it up near the fry tank and use the same airpump with a gang valve to drive the airstones to save on equiptment costs. If your water quality is bad (ammonia or nitrites) "borrow" some filter media from the main tanks filter and put it in your filter or near the flow of your filter. Good Luck. Raising fish from pups is an awesome experience.