Feeding and Nutrition

Everything an animal is built from comes from what it eats: growth, energy, color, resistance to disease and the ability to breed. Good water can't make up for a poor diet.

Food is also the largest input to a system. Whatever goes in either becomes part of an animal or ends up as waste: uneaten food and droppings break down into ammonia, nitrate and phosphate (Module 8). So feeding is always two jobs at once: feeding the animals and managing what the food does to the water.

Herbivores, such as tangs, graze algae and seaweed through the day. Carnivores eat meaty foods. Omnivores, such as clownfish, eat both. Planktivores pick small drifting food from the water, a little at a time and often. Filter feeders, such as clams, strain tiny particles out of the water.

Clams, corals and anemones are also photosynthetic: algae living in their tissue turn light into food for them. Light isn't their only food, though, and they still feed. Before an animal is bought, find out what it eats (Module 24); a fish fed the wrong kind of food can starve with food in front of it.

Dry pellets and flakes are easy to measure and store, and good ones are complete diets, but they lose vitamins once the container is opened. Frozen foods, such as mysis shrimp, are close to natural prey. Seaweed sheets feed grazers through the day. Live food moves, and the movement triggers feeding, which is why it works for newly arrived fish that refuse other food and for larvae.

No single food has everything. Rotating several foods through the week covers what any one of them lacks, and keeps animals taking a range of foods.

An animal's mouth sets the size of food it can eat. A fish that takes a pellet and spits it out may be telling you the pellet is too big. Newly hatched fish larvae can only take very small prey, such as rotifers, which measure about 100 to 340 microns. A micron is one thousandth of a millimeter.

A reef system holds mouths of every size: fish, corals, clams, worms, and the tiny animals living in the rock and sand. Feeding a range of particle sizes, from phytoplankton up to pellets, feeds every level of that food web, not only the fish.

A meal is the amount that gets eaten within a few minutes. Most adult fish do well on small meals once or twice a day. Young fish and very active fish need several small meals a day. Grazers do best with seaweed available through the day.

Fish always act hungry, so begging is no guide. Watch what's actually eaten, and adjust: if food reaches the bottom and stays there, it was too much.

Overfeeding is the most common feeding mistake. Uneaten food rots and releases ammonia, and nitrate and phosphate build up and feed algae. Ammonia, nitrate and phosphate aren't simply waste: at the right concentration they're food for corals, clams and algae, and at zero the animals that use them go hungry. The harm comes from too much.

Underfeeding shows on the animals: thin bodies, pinched bellies, slow growth, dull color and more fighting over what food there is. The answer to dirty water isn't starving the animals. Feed what gets eaten, and remove leftovers.

A healthy fish comes out and eats. A fish that ignores food is often the first sign of trouble, before anything else shows. Some fish, clownfish among them, rest on the bottom and can look sick; when food goes in, a healthy one springs out and eats. Count heads at every meal.

Watch who gets the food. A bold fish can take everything while a shy or new one gets none. Feeding in two places at once, or placing food near the shy fish, makes sure every animal eats (Module 24).

Anemones are carnivores. Their tentacles grip whatever lands on them and carry it to the mouth, at the center of the oral disc. The food is raw, meaty and marine: pieces of fish, shrimp, mysis, krill, scallop or clam, in variety. Cooked or seasoned food isn't used.

Cut each piece smaller than the anemone's mouth. Small pieces are digested more easily and are less likely to come back up. Turn the flow down or off so the food isn't blown away, then place the piece on the tentacles with tongs or a feeding tube and let go. A healthy anemone's tentacles feel sticky and hold the food, then fold it in toward the mouth. Never push food into the mouth: the mouth tears easily. Start a small or newly settled anemone on small pieces and a small amount, and increase as it keeps its meals down. A new anemone isn't fed until it has attached and settled.

Target feeding is commonly done once or twice a week. More food means faster growth, up to what the anemone can digest. In a heavily fed tank an anemone also catches food meant for the fish, and clownfish carry food to their own anemone: in field trials, anemones fed only by their clownfish grew about as well as anemones fed by hand. Fish and shrimp also steal, so watch until the meal is swallowed, or feed the fish first.

An anemone that spits food out hours later was given a piece that was too big, or was fed again too soon. Take the spat-out food out of the tank and feed less next time. An anemone that has lost its color still needs food, in small, easily digested pieces. An anemone whose tentacles aren't sticky and won't hold food, or whose mouth is gaping, is showing a sign of trouble (Module 30).

Broadcast feeding puts food into the water for everything that filters or catches it. Target feeding places food on one animal. Corals with large polyps and anemones are target fed pieces they can hold. Corals with small polyps have hundreds of tiny mouths on one colony, so they're fed by broadcast, as are giant clams, sponges and feather worms.

Each group takes a different size. Phytoplankton, at about 2 to 20 microns, feeds giant clams, soft corals, sponges and worms, and it feeds the rotifers and copepods living in the system, which become food in turn. Rotifers and fine powdered foods, roughly 40 to 200 microns, suit small-polyp stony corals. Mysis and chopped seafood, 1 mm and larger, suit large-polyp corals and anemones. A food of one size feeds one group, so a mixed reef is fed a mix of sizes.

To broadcast feed, mix the food with a cup of tank water first; a dry powder that isn't wetted floats or clumps. Turn off the skimmer and take mechanical filtration out of the path, or they remove the food before it's eaten. Pour the mix into strong flow and leave the circulation pumps running so the food stays suspended. Turn the filtration back on after 15 to 30 minutes. Feed when the polyps are out: for many corals that's after the lights go down, and some take food best in the morning. For target feeding, turn the pumps off, put a thicker mix or a piece onto the polyps with a pipette, and turn the pumps back on once it's been taken.

What isn't caught becomes nutrients. Start with a small amount, raise it slowly, and follow nitrate, phosphate and algae as you do (Module 17).

A coral has two sources of food. The algae living in its tissue use light to make sugars, which give the coral energy. The polyps also catch food from the water, which gives energy and the protein that new tissue is built from. Light alone doesn't supply enough of that building material.

Feeding changes growth. In trials with one stony coral under the same light, fed colonies grew two to eight times more tissue than unfed ones, and built skeleton about 30% faster. Under low light, feeding can keep a coral's skeleton growing. Some corals go further: a Montipora that had lost its algae met all of its daily energy needs by feeding alone. Other corals in the same trial couldn't, so it depends on the coral. A coral that's growing poorly under good light and good water may be short of food, so check the feeding before adding more light.

The food has to fit, and it has to be food the coral can use. The mouth of a flowerpot coral (Goniopora) is only 50 to 100 microns across, so it can't swallow large prey; in a trial it grew best on a very fine, protein-rich prepared food, better than on yeast or phytoplankton. Another coral ate newly hatched Artemia readily and didn't grow any faster. Taking the food isn't proof that it's helping: growth is. Timing can matter too: the flowerpot coral digested best in the morning (Module 27).

Corals and filter feeders do better on many small meals than on one large one, and much of a large one is filtered out before it's eaten. A dosing pump on a timer (Module 19) can add liquid food in small doses through the day and night: phytoplankton, rotifers, or a liquid coral food. Automatic feeders for dry food do the same job for fish.

Food isn't a supplement, and it spoils. A food that's stored in a refrigerator goes bad in a container at room temperature and grows mold. Its container sits in a small refrigerator, or a food made to keep at room temperature is used. Particles settle, so the container is stirred or shaken, or a live culture is kept bubbling with air.

Send the dose into strong flow in the display, not into the skimmer or a filter sock. Smell and look at the food when the container is refilled: food that has gone off is thrown away, not fed.

Phytoplankton is tiny drifting algae. Rotifers and copepods eat phytoplankton, and larvae, small fish and corals eat the rotifers and copepods. Newly hatched Artemia, or brine shrimp, are a larger live food for bigger larvae and small fish. Fish larvae often can't be raised without live food: it's small enough, and its movement makes them strike.

Cultures are kept clean and apart. A few rotifers carried into a phytoplankton culture will eat it, so each culture has its own tools and phytoplankton is handled first. Cultures can crash without warning, so a backup of each is kept running.

Live prey is only as nutritious as what it has eaten. Rotifers and Artemia are low in the fatty acids DHA and EPA that marine fish larvae need, so before they're fed out they're enriched: fed a food rich in those fatty acids. Enrichment fades as the prey uses it up; within hours it drops, and a day later the prey is no longer enriched. Enriched prey is fed out soon.

Stored food loses value too, vitamins first. Dry food kept beside a warm, humid tank goes off fastest: keep it cool, dry and sealed, away from the tank, and replace it within 3 to 6 months of opening. Frozen food stays frozen until it's used, and is never thawed and refrozen. Old food can look fine and still feed poorly.

Work from what you see. Algae spreading with food on the sand points to the amount. One thin fish among healthy ones points to who's getting the food, or its size. A thin grazer points to the type of food. A whole tank that's dull and growing slowly points to old food or too little variety. Larvae that fail point to prey size and enrichment timing.

More than one of these is often true at once: the food is stale and there's too much of it; the pellet is too big and the bold fish takes it first. Check them all, then fix each cause.