Would you feed a hamburger to a week-old infant? Of course not! Not only would the baby be physically unequipped to chew and digest it, but it wouldn't contain the right balance of nutrients necessary for his or her stage of development.
Â Like newborn humans, newborn fish need special foods, and plenty of them. Unlike adult fish, which can typically go a week or two without food, fry can starve to death within a day if they don't have enough to eat. And even if they do survive, malnourished fry probably won't grow well, and may develop problems such as curvature of the spine.
Â While you'll need to feed livebearer fry shortly after they're born, do not feed the fry of egg-laying species until they are free swimming - that is, able to swim on their own-something that usually takes a few days to a week after they hatch. Until then, the fry will remain stationary, feeding off the remnants of their yolk sac-a membrane-enclosed cocktail of fats, proteins, and other substances, visible as a pouch extending from their belly. But once they use this up, you will need to feed them several times a day.
Â From the outset, some fry, including those of most livebearers, will be big enough to eat regular flake food crushed into a powder. But fry of many other species are so small that the only things that they're able to fit in their mouths are microscopic organisms known as infusoria.
Â What follows are some common first foods for fry. Many call for starter cultures, which you can obtain either from a biological supply company (check the Internet) or from other hobbyists.
Â Commercial Fry Food
It is available in both liquid and powdered forms, and in formulas for livebearers and egg-layers. Fry food isn't just a ground-up version of the flakes fed to adult fish; rather, it has a nutritional balance that takes into account the accelerated growth rates of fry. Probably the easiest way to feed your fry, but some breeders claim fry fed exclusively on prepared foods will not grow as rapidly or be as robust as those fed a varied diet that includes live foods.
Â Green Water
This is just water with unicellular algae in it, often used as a first food for fry, as well as to culture daphnia and some other live foods. To make, fill ajar with tank water and set in a sunny location until the water turns green. You can also add small, smooth rocks, which will grow a coat of algae that can be used to feed plecostomus fry and other bottom-feeding herbivores.
This is a catchall name for microscopic organisms such as protozoa and unicellular algae, which provide an excellent first food for tiny fry. Culturing your own is simple: Place vegetable matter, such as a couple of crumpled leaves of lettuce (make sure it's pesticide-free) or a small chunk of boiled potato, in ajar and pour tank water over it. Set in a warm, dark place but do not cover, since the spores from which infusoria grow are airborne.
Within a day or two, you'll notice that the water becomes cloudy as the infusoria begin to grow. This water can be added to the rearing tank with an eyedropper. Some breeders simply drop crushed lettuce leaves into the rearing tank as soon as the fry hatch; by the time they're free swimming, infusoria will have developed. The downside to this is that the decomposing lettuce leaves can pollute the water, so if you use this method, you'll need to monitor water quality carefully.
Â Baby Brine Shrimp (Naupulii)
This is one of the most nutritious foods for fry, and can be fed to all but the smallest of them. Make sure that you use them within 24 hours of hatching (and preferably less), since the naupulii will use up their yolk sacs after that and their nutritional value will decrease.
Another highly nutritious fry food that is easy to produce. Start by cooking a small quantity of regular unsalted oatmeal. Spread in a small plastic container, such as a margarine tub, to a depth of about half an inch, and cool to room temperature. Add a spoonful of worm culture and sprinkle lightly with baker's yeast. Within a few days, the culture will start to look soupy, an indication the worms are multiplying.
To harvest, warm the container slightly by placing it under a lamp or on top of the tank light; within 20 minutes or so, the worms will begin climbing the sides of the container and can be scraped off with a spoon or your finger. Rinse and feed to fry with an eyedropper. One disadvantage of microworms is that they sink to the bottom of the tank, and surface-feeding fry sometimes have a hard time finding them.
Â Vinegar Eels
Despite the name, these aren't actually eels-they're nematodes that grow no larger than one-sixteenth of an inch. Their tiny size makes them an excellent first food for fry, and unlike microworms, they swim throughout the water column, making it easy for fry to find them. They're also easy to grow: All you have to do is fill a gallon container-a plastic milk jug, well rinsed, is fine-about two-thirds of the way with equal parts dechlorinated water and apple cider vinegar. Add half an apple sliced to fit through the neck of the bottle (it's not necessary to peel or core) and a vinegar-eel culture.
Cover the mouth of the jar with cloth to let air in and keep other insects out, then store at room temperature. In about a month, if you hold the container up to a bright light and look closely, you'll see the eels, which resemble barely-visible slivers of glass.
To harvest, pour the medium through a coffee filter and rinse in lukewarm tap water, then swish it in the fry tank. One advantage to feeding vinegar eels is that they can live in the tank for several days; in a pinch, you can put some in the tank in the morning and simultaneously supply your fry with breakfast, lunch, and dinner without worrying about the effect of decomposing food on water quality.
Â Hard-Boiled Egg Yolk
Many prepared fry foods contain egg yolk, but you don't have to buy commercial foods to give your fish the benefits of this excellent protein source. Instead, wrap the yolk of a hard-boiled egg tightly in a fine-mesh cloth, dunk it in the tank, and squeeze it gently under water. This forces tiny particles of the yolk through the cloth and into the tank, where the fry can get them.