Introduction

In contrast to aquaculture, where diets are tailored to a single species, feeding a large mixed reef environment can be both frustrating and challenging. With the exception of essential fatty acids, nutritional requirements of warmwater fish do not vary greatly among species (Brown and Gratzek, 1980). Considerable variation does exist, however, in the form of food a given species will accept.

Reef fish in a natural environment consume a wide variety of foods. Herbivores, omnivores, carnivores, and top predators are part of an intricate food web. The complexity of this ocean ecosystem is not fully understood, and at this time without duplication. Any marine aquarium, regardless of how large or carefully designed, is not a slice of the ocean. It at best provides the minimum requirements to support selected species of marine life. And duplication of natural diets is impractical if not impossible. Aquarists are therefore challenged to provide their animals with nutritionally satisfying diets in a form they will readily accept without extensive training, while simultaneously discouraging predation.

Discussion

At the Living Seas, many of the fishes' "natural" foods are stocked in frozen form. Clam, krill, shrimp, squid, smelt and herring of "restaurant quality" are slow thawed (under refrigeration) for minimal bacterial buildup. These are then, if necessary, chopped to various sizes and in two feedings per day distributed throughout our 5.7 million gallon main environment. Depending upon target animal and type of food, methods of dispersal may include broadcasting across the tank surface, distribution by divers at the reef level, or in many cases actual handfeeding of non-aggressive species and those requiring special attention. The seafoods are well received and provide many nutrients. A simplified nutritional breakdown is included in Table 1. A nutritional comparison of our combined diet and two commercial feeds is made in Table 2. In addition to the aforementioned foods many of our fish, as evidenced by studies on natural populations (Randall and Bishop, 1967), require substantial amounts of vegetative material in their diets.

Table 1. Nutrient Content of Foods Provided at the Living Seas

Table 2. A Nutritional Comparison of the Living Sea's Diet vs. Fish Chow

For aesthetic reasons sessile microalgaes are discouraged from growing in our system. Macroalgaes and vascular plants would suffer from insufficient light and unrelenting pressure from grazers. As a result, dietary plant material must be provided from alternate sources. While many terrestrial vegetables have been tried by aquarists throughout the years, romaine lettuce and more nutritious spinach are still favorites.

Sixteen to twenty heads of romaine and 9 pounds of frozen spinach are fed each day. A problem to be dealt with most vegetables is their buoyancy. In the case of a weighted stainless steel lag bolt is screwed into the core of the lettuce head. This enables a diver to place the lettuce at will anywhere along the "reef". The frozen spinach is placed in specially designed, weighted racks, allowing the fish to effectively feed through "windows" on each side. Angelfish, surgeonfish, parrotfish, and sheepshead, among others, make quick work of these foods.

Not only are herbivores specially fed, top carnivores are given extra care. Herring, mackerel and bonita are surface fed every other day to our tiger, bull and brown sharks. At each feeding they receive a multivitamin/mineral supplement, 300mg potassium iodide, 500mg vitamin B1, 10,000iu. vitamin A, and 600iu vitamin E. Similar vitamin/mineral supplements are given to most of our other predators on a case-by-case basis. Actual vitamin/mineral requirements of captive held sharks is poorly understood. However, we theorize that dietary induced diseases occurring in other types of wildlife, are likely to occur in fish, particularly captive held predators. Dietary deficiencies of iodine can lead to goiter in many animals. Deficiencies in vitamin B1 can occur in animals fed diets of fish high in thiaminase, such as herring or smelt. Some mammals, notably ruminants, show inability to convert betacarotenes to vitamin A when high levels of nitrate are present in the diet. Additionally, high levels of dietary goitrogens, such as nitrate fertilizers, will produce goiter in ruminants even when adequate dietary iodine is present. Vitamin E deficiencies have occurred in reptiles fed foods high in polyunsaturated fats, such as mackerel or herring (Hoff and Davis, 1982). Relationships between the occurrence of goiter in captive sharks and the inevitable presence of high levels of nitrate in aquarium water deserves closer examination. It should also be noted that all of these predators are kept with potential "forage" fish. The degree to which they "snack" is difficult to determine. Most reported occurrences of freefeeding are associated with our bull sharks.

As an added nutritional boost for the rest of the fish, sinking pelleted foods (trout chows) are broadcast over the surface of the reef environment and are eaten by many of the pelagic swimmers (chub and pompano) as well as reef dwellers (grunts, angel, butterfly and surgeonfish). The pellets are coated, or "top-dressed", with ascorbic acid (500mg/1) and crayfish oil (25g/1) for added pigmentation, and are placed in a freezer for 24 hours to allow for absorption of the oil prior to use.

Another specially prepared food (made primarily for the parrotfish) is a dental plaster food block. In the wild, parrotfish feed mainly on algae and use a pharyngeal mill to grind soft coral rock or sand together to break down the plant materials (Randall and Bishop, 1967). Since the coral pieces at the Living Seas are artificial, a substitute for this "grit" is required. Dental plaster (Whip Mix Corporation, Laboratory Plaster) is a soft, quick-setting plaster that the parrots can crush. During preparation, top-dressed pellets are added to the wet plaster before it hardens in the mold. For extra pigmentation in the fish, a canthaxanthin compound (LaRoche Labs, Roxanthin Red) is mixed into the block at 0.63mg compound/liter of plaster. These "pink bricks" are placed in the main environment at an average of three blocks per day. An increase in pink, orange and red coloration in the fish has been noticed over time (especially when compared to newly introduced parrots).

The Living Seas staff provides "natural" and artificial foods to a variety of marine animals. However, the sheer volume of water and reverse flow filtration of our main environment precludes support of strictly planktivorous animals. A staple food used throughout the aquarium and aquaculture field, is brine shrimp, Artemia salina. Use of brine shrimp in our main environment is limited but we do make considerable use of it in peripheral systems and aquaria. We are not raising brine shrimp at this time. They are purchased as adults from a local supplier. Adult brine is an effective vehicle for delivering added nutritional materials or medications to fish, and most small marine tropicals will consume it with relish. our brine shrimp are continuously fed microalgaes (specifically: Isochrysis spp., Nannochloris spp. or Chaetocerous spp.) prior to being used as food for our fish. Additionally short term immersion of live brine shrimp in solutions of Aminoplex, nitrofurazone, Roxanthin Red, among others, allows for absorption of these materials by the shrimp for ultimate delivery to a fish.

At this writing, our principle concerns for improving nutrition at the Living Seas are: limiting fat content of overall diet, effectively targeting specific species of fish for consumption of desired foods and incorporating more essential vitamins, minerals and color enhancers within the diet.

References

1.  Brown, E.E. and Gratzek, J.B. 1980. Fish Farming Handbook. AVI Publishing Co., Inc. Westport, Conn.

2.  Hoff, G.L. and Davis, J.W. 1982. Noninfectious Diseases of Wildlife. Iowa State University Press. Ames, Iowa.

3.  Randall, J.E. and Bishop, B.P. 1967. Food Habits of Reef Fishes of the West Indies. Proc. Int. Conf. Trop. Ocean., October, 665-847.

4.  Sidwell, V.D. 1981. Chemical and Nutritional Composition of Finfishes, Whales, Crustaceans, Mollusks and Their Products. U.S. Dept. of Commerce, N.M.F.S. 432pp.

5.  Winfree, R. 1988. pers. comm. Harbor Branch oceanographic Institution.