Nutritional Management of Marine Mammals: A Review
IAAAM Archive
Jesse R. White, DVM; Ruth Francis-Floyd, DVM, MS

The specific nutritional requirements of marine mammals have not been determined. Successful captive management and reproduction has resulted from improvements in nutrition and husbandry largely arrived at through application of common sense practices, trial and error, and careful management and observation.

The nutritional value of common food items, and successful food handling practices, will be briefly reviewed. An overview of reported nutritional disorders of cetaceans and pinnipeds will follow. Finally a brief discussion of nutritional management of sirinians and sea otters will complete the review.

Nutritional Value Of Food Items

For most captive marine mammals a large portion of the diet consists of fish which have been frozen for a period of time prior to feeding. Commonly fed species include herring (Clupea harengus), mackerel (Scomber scombrus), smelt (Osmerus mordax), and capelin (Mallotus villosus). Although the nutritional value of fish is variable, a principal consideration for nutritional management is the fat content of species fed. Herring and mackerel are oily fish with a comparatively greater fat content then smelt or capelin. Invertebrates such as squid (Ilex sp. and Loligo sp.) have even less fat than light fish such as smelt or capelin. The greater the fat content of a species of fish, the greater the available energy (Kcal/ kg) in a given food item. Nutritional management of a debilitated animal therefore would logically include a greater percentage of high energy, or oily, fish in the diet. Conversely, a mature animal on a maintenance ration would be fed a comparatively smaller percentage of oily fish. Extra energy demands for growth, reproduction, lactation, or performance should be considered when developing feeding recommendations for individual animals.

An important source of fresh water for marine mammals is from the moisture content of food items. Fish such as capelin and smelt, and invertebrates such as squid, have a higher moisture content than oily fish such as herring or mackerel. Fresh water can be injected into food fish for debilitated animals or in situations where there is concern about hydration status.

A variety of food items should always be fed to provide a balance of nutrients. All fish are considered high quality protein but amino acid composition and nutritional value varies for different types of fish. Storage and handling can have a marked effect on wholesomeness, as will be discussed. Carbohydrate content of fish is low. Invertebrates are preferred as a source of carbohydrates (Geraci, 1981).

Storage and handling of seafood products can seriously affect vitamin and mineral content of food items. In many cases vitamin and mineral supplementation is warranted. At the Miami Seaquarium, cetaceans and pinnipeds were fed daily supplements of vitamins C, B1, A and E, in addition to a multivitamin and mineral product. Vitamin and mineral supplements were fed daily, at least one hour prior to the first feeding of the day. Dose of vitamins given to an individual animal was determined following consideration of reproductive status, health status, work status, and age. For example, during late gestation and lactation a calcium-phosphorus supplement was added to the diet. Clinically, these protocols appeared to be associated with decreased incidence of respiratory disease, decreased incidence of chronic or sporadic periods of inappetence among individual animals, and improved reproductive performance. Vitamin and mineral supplementation of sirinians was associated with a dramatic improvement in reproduction.

Handling And Storage Of Food Items

The Federal Register (1979) specifies that food preparation for marine mammals should be conducted so as to minimize bacterial or chemical contamination and to assure wholesomeness and nutritive value of the food. Skin and scales of healthy fish are contaminated with bacteria from the aquatic environment. Common sense would dictate that rough handling of fish, particularly breaks in the skin, would allow contamination of internal tissues and hasten spoilage. Poor sanitation can result in rapid growth of potentially pathogenic bacteria and result in contamination of food items through contact with dirty buckets and utensils.

Food handling facilities should be spotlessly maintained and porous surfaces avoided. Buckets should be thoroughly cleaned and disinfected after each feeding; sinks should be cleaned and disinfected at the end of each day.

Federal law requires that fish to be fed to marine mammals be stored at temperatures of -18C (Federal Register, 1979). To prevent "freezer burn" or dehydration of frozen fish the freezer should be maintained with as high a relative humidity as practical (White, 1968).

Maximum storage time varies for different species of fish. In general, the greater the fat content of a fish, the shorter the storage time. For mackerel, 4 months storage at -18C is probably the maximum safe allowable storage time. This time period will be markedly decreased if fish are partially spoiled when frozen. Ideally, fish should be flash frozen with a glaze of ice immediately after they are caught. This process retards decomposition and improves moisture content of fish. Light fish such as smelt can be safely fed after a longer storage, six months is a reasonable maximum storage for these fish.

Prior to thawing, fish can be moved from the freezer into a cool room (maintained at 15C to 20C) for up to 12 hours. Fish can then be thawed in cold tap water. This slow-thaw minimizes the loss of water soluble nutrients. No food shall be fed to marine mammals more than 24 hours after it has been removed from the freezer (Federal Register, 1979).

Frequently it is necessary to fish into small chunks to increase the number of rewards available for animals in training or shows. New behavioral techniques involving variable reinforcement schedules which are not based solely on food reward systems may decrease the need for feeding cut fish. When cut fish must be fed, there is a loss of vitamins resulting from removal of the viscera. Also, the interior of the fish is contaminated with bacteria, thereby dramatically decreasing the time required for spoilage to occur.

Nutritional Disorders Of Cetaceans

Thiamine Deficiency

Thiamine deficiency has been reported in an Atlantic bottlenosed dolphin (White, 1970), California sea Lions (Ridgon and Dragger, 1955),and gray seals (Meyers, 1955). The disorder is caused by thiaminase which may be present in several species of fresh and salt water raw fish (Deutsch and Hasler, 1943); Geraci, 1968; Green et. al., 1942). The activity of the compound may be related to the state of putrefaction of the fish in that certain amines are potent activators of thiaminase (Deolalkar and Sohonie, 1957a; Deolalkar and Sohonie, 1957b).

Thiamine deficiency in an Atlantic bottlenosed dolphin (Tursiops truncatus) was first reported in 1970 (White, 1970). The adult female dolphin had been fed 6.4 to 7.3 kg of raw fish daily. Although 3 species of fish were fed, more than 50% of the diet was herring. The animal was fed a multivitamin supplement daily. Initially, the dolphin refused to perform, and she became progressively anorectic. Clinical findings were non­specific. No improvement was noted following supportive treatment with broad spectrum antibiotics. For 3 weeks the animal continued to deteriorate. Clinical signs and diagnostic tests did not support a bacterial etiology, and respiratory and gastrointestinal diseases were ruled out. Supportive therapy was continued, and the animal was treated with 1800 mg thiamine HCl intramuscularly, and 200 mg thiamine HCl intravenously with 1 1 lactated ringers solution. Six hours following administration of thiamine the dolphin began eating and she progressively improved, gained weight, and was clinically normal within 1 month.

In 1980, a female killer whale (Orcinus orca) became erratic in her performance, and progressively developed anorexia. Vitamin supplementation with vitamins C, B1, A, E, and a multivitamin mineral product, were doubled. Simultaneously several other animals at the park, including Atlantic bottlenosed dolphins and California sea lions began delivering poor performances and became sporadically anorectic. As the condition of the killer whale worsened a clinical diagnosis remained elusive. She showed no response to treatment with broad-spectrum antibiotics or ketoconazole. Although trained to present her fluke for venipuncture, her refusal to work resulted in the decision to drop the tank for collection of a blood sample. While she was "beached" thiamine HCl was administered intramuscularly. Clinical improvement resulted within 24 hours. Thiamine supplementation was increased for all animals on the grounds, behavioral and appetite problems resolved. Although a direct cause and effect relationship was not proven, a shipment of very fatty herring had been received and was being fed to all animals on the grounds beginning just before the problems started. The occurrence of a generalized malaise among different species of animal, kept in different areas and systems, and cared for by different handlers is supportive of a nutritional etiology. The response to thiamine is supportive of a degree of thiamine deficiency, possible related to an excessive thiaminase content in that particular shipment of herring.

Vitamin E Deficiency

Geraci (1981) mentioned an incident involving 2 amazon dolphins (Inia geoffrensis) which were affected by weakness and 37-steatitis. ne animal also suffered from hemolytic anemia. A definitive diagnosis was not achieved in this case, however a nutritional etiology was suspect. Vitamin E deficiency is discussed in greater detail in the section on pinnipeds.

Vitamin Deficiency

Tissue assays from stranded cetaceans suggest that ascorbate concentration is independent of dietary intake (St. Aubin and Geraci, 1980). Studies on captive animals fed nonsupplemented diets suggest that food fish are adequate as a source of vitamin C (Geraci, 1981). Miller and Ridgway (1963) reported a Pacific white-sided dolphin (Lagenorhynchus obliquidens) affected by gingivitis, glossitis, pharyngitis, and necrotic stomatitis.

These signs were considered suggestive of vitamin C deficiency, and ascorbic acid therapy was associated with clinical improvement. A definitive diagnosis of vitamin C deficiency was not made, however, because of the lack of blood ascorbate determinations. There is disagreement regarding the need for vitamin C supplementation, but the authors' clinical experience support a recommendation for daily ascorbic acid supplementation.

Fish Induced Anemia

Fish induced anemia has not been demonstrated in captive marine mammals. It is a recognized syndrome in terrestrial mammals (Stout et. al., 1960), and is associated with feeding thawed raw gadoid fish, but not with the feeding of fresh fish (Havre et. al., 1967; Ender and Helgebostad, 1968). Anemia results from interference with iron absorption caused by heat-labile substances in the fish (Stout et. al., 1960). Clinically, the condition responds to parenteral iron therapy but not to oral iron therapy (Stout et. al., 1960; Leekley et. al., 1966). Geraci (1981) speculates that fish-induced anemia may play a role in some cases of non-specific anemia in captive cetaceans which are non responsive to oral iron therapy (Medway and Geraci, 1978).

Scombroid Poisoning

Geraci and Gerstmann (1966) reported a suspected case of histamine toxicosis in an Atlantic bottlenosed dolphin fed mackerel. Principal findings included peptic ulcers in the first stomach chamber, and hemorrhagic erosions in the second chamber. Scombroid poisoning, which resembles histamine toxicosis, has been reported in humans (Kawabata et. al., 1955; Listick and Condit,, 1964). Geraci (1981) suggests that a diet composed largely of mackerel, particularly if improperly stored, may be related to non-specific disorders in marine mammals which respond to a change in food type. Geraci (1981) discusses a dolphin which had been inappetant for a prolonged period after it had been fed rancid mackerel and serum histamine appeared to be elevated. Geraci (1981) suggests storage of fatty fish, particularly mackerel, be limited to no more than 3 to 4 months, and that freezer temperatures be maintained at -30C.

Nutritional Disorders of Pinnipeds

Thiamine Deficiency

Thiamine deficiency has been discussed. Thiamine deprived harp seals (Phoca groenlandica) develop clinical signs of thiamine deficiency in 40 to 60 days. Affected animals become anorectic and unresponsive to the environment. Respiratory irregularities are followed by tremors, muscle spasms, head shaking, and death (Geraci, 1972). Diagnosis is confirmed by demonstration of a 25% increase in red cell transketolase activity following administration of thiamine (Geraci, 1972; Geraci, 1974). Geraci (1972) recommends thiamin supplementation be provided twice weekly. He suggests providing 5 mg, administered 2 hours before the first feeding, be provided for every 1000 Kcal of fish fed per day. Alternatively, he suggests supplementing 25 mg thiamin for each kg fish fed as part of the regular feeding.

Vitamin E Deficiency

Citino et. al. (1985) reported fatal nutritional myopathy in a California sea lion deprived of vitamin E supplementation for 32 days. The diagnosis was confirmed by a low plasma vitamin E concentration. Clinically, the animal was lethargic and anorexic prior to death. The animal was weak, and alopecia was noted behind the foreflippers and around the eyes and mandible. The sea lion became extremely dyspneic when restrained. Gross pathology was suggestive of white muscle disease. Necrosis and inflammation of muscle tissue was reported in addition to renal tubular degeneration, possible related to myoglobinuric nephrosis. Engelhardt and Geraci (1978) recommend 100 IU of vitamin E per kg of fish fed be provided as a daily supplement when fish have been frozen for more than 4 months prior to feeding.

Pinniped Hyponatremia

Pinniped hyponatremia was first reported by Hubbard in 1968 (Hubbard, 1968). The condition occurs in pinnipeds kept in fresh water environments and is characterized by gradual or sudden decreases in plasma sodium and plasma chloride. Plasma potassium may or may not change. Affected animals become anorectic and very weak. Neurologic signs may precede death. Hyponatremia should be on a differential diagnosis for sudden death in pinnipeds. The condition appears to be most common in stressed animals (Geraci, 1981). Low plasma sodium (< 147 mEq/1) and chloride values confirm the diagnosis of Hyponatremia. Treatment of affected animals with NaCl replacement therapy (Geraci, 1972) is frequently successful. All pinnipeds maintained in fresh water, and any which have survived a hyponatremic event, should receive a daily NaCl supplement. Geraci (1981) recommends 3 g NaCl/ kg fish fed/ day for pinnipeds maintained in fresh water. Squid, which has a high salt content, is an excellent food item for animals which have a recurrent problem.

Disaccharide Intolerance in Pinnipeds

Schroeder (1933) reported milk protein hypersensitivity in a walrus fed condensed milk. Geraci (1981) suggests that this may have been the first report of disaccharide intolerance in pinnipeds, although it was not recognized as such. Pinniped milk does not contain complex carbohydrates (Ridgway, 1972). Complex sugars are probably not digested and can act as a bacterial substrate in the gut, contributing to enteritis and diarrhea (Geraci, 1981). The condition should be suspected in pups which develop diarrhea when reared on artificial formulas.

Nutritional Management of Sirinians

Effect on Reproduction

The free ranging West Indian manatee (Trichichus manatus) eats a wide variety of aquatic plants (Hartmann, 1979; Best, 1981; Bengston, 1983). Observations of wild animals by Hartmann (1979) suggested that there was no obvious preference of available plants and that feeding was rather opportunistic. The quantity of aquatic plants or green vegetables required for any given animal will vary not only with the type of plant ingested, but also with the season it is consumed, its chemical composition, the efficiency with which it is consumed, and the physiologic status of the animal.

Several facilities in Florida have successfully maintained individual manatees for more than 20 years. Two animals collected in 1957 and 1958, respectively, remain reproductively active and the female is currently expecting her fifth calf. Successful captive breeding was not realized until improvements in nutritional management were instituted in the early and mid 1970s (White 1984).

Prior to 1972, captive manatees at the Miami Seaquarium were maintained on a diet of iceberg and romaine lettuce. Although copulation was observed, pregnancy never resulted. Beginning in 1972 and 1973 the manatee diets were improved by the addition of high protein monkey chow, fresh carrots and bananas. In addition a daily multivitamin-mineral and calcium-phosphorus supplement were added. The first calf was born in 1975.

In 1980, hydroponically grown oat sprouts were added to the manatees' diet and reproductive activity increased dramatically.

Effect on Skin Lesions

Captive manatees at the Miami Seaquarium were sporadically affected by pox like skin lesions. The lesions were raised, circular, and yellow in color. Scanning electron micrographs of lesion biopsies did not reveal virus particles. The lesions appeared to resolve when vitamin C supplementation was increased.

Nutritional Management Of Sea Otters

Sea otters (Enhydra luteus) are successfully maintained at the Monterey Bay Aquarium on a varied diet which includes Quoydock clams, abalone, whitefish and rockfish. No vitamin or mineral supplementation has been necessary (T. Williams, pers. comm., 1988).


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Speaker Information
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Ruth Francis-Floyd, DVM, MS, DACZM
Department of Large Animal Clinical Sciences
Department of Fisheries and Aquatic Sciences
University of Florida
Gainesville, FL, USA

Jesse R. White, DVM