Thyroid hormone concentrations in captive and free-ranging West Indian manatees (Trichechus manatus).

Because thyroid hormones play a critical role in the regulation of metabolism, the low metabolic rates reported for manatees suggest that thyroid hormone concentrations in these animals may also be reduced. However, thyroid hormone concentrations have yet to be examined in manatees. The effects of captivity, diet and water salinity on plasma total triiodothyronine (tT(3)), total thyroxine (tT(4)) and free thyroxine (fT(4)) concentrations were assessed in adult West Indian manatees (Trichechus manatus). Free-ranging manatees exhibited significantly greater tT(4) and fT(4) concentrations than captive adults, regardless of diet, indicating that some aspect of a captive existence results in reduced T(4) concentrations. To determine whether this reduction might be related to feeding, captive adults fed on a mixed vegetable diet were switched to a strictly sea grass diet, resulting in decreased food consumption and a decrease in body mass. However, tT(4) and fT(4) concentrations were significantly elevated over initial values for 19 days. This may indicate that during periods of reduced food consumption manatees activate thyroid-hormone-promoted lipolysis to meet water and energetic requirements. Alterations in water salinity for captive animals did not induce significant changes in thyroid hormone concentrations. In spite of lower metabolic rates, thyroid hormone concentrations in captive manatees were comparable with those for other terrestrial and marine mammals, suggesting that the low metabolic rate in manatees is not attributable to reduced circulating thyroid hormone concentrations.

Effects of capture on adrenal steroid and vasopressin concentrations in free-ranging bottlenose dolphins (Tursiops truncatus).

Marine mammals are routinely caught in the wild in an effort to monitor their health. However, capture-associated stress could potentially bias various biochemical parameters used to monitor the health of these wild caught animals. Therefore, the effects of capture were quantified by measuring plasma adrenal steroids and arginine vasopressin (AVP) in free-ranging bottlenose dolphins (Tursiops truncatus) (n=31). Total capture and restraint times were also correlated to hormone concentrations to quantify the effects of capture. Significant, positive correlations between corticosterone and cortisol (R=0.752; P<0.0001), and between corticosterone and aldosterone (R=0.441; P=0.045) were demonstrated. Significant correlations between capture and restraint time and hormone levels were not observed. Animals restrained for less than 20 min exhibited hormone levels similar to those for animals restrained for more than 20 min. The positive correlations among the adrenal steroids suggest that release of these steroids was stimulated by adrenocorticotropin (ACTH). The lack of a correlation between cortisol and AVP indicates that AVP did not influence ACTH-induced cortisol release in this situation. The study suggests that (1) a typical hypothalamic-pituitary-adrenal axis is present in these animals, and (2) the relatively short capture and restraint times did not induce a significant neuroendocrine stress response.

Estimation of water turnover rates of captive West Indian manatees (Trichechus manatus) held in fresh and salt water.

The ability of West Indian manatees (Trichechus manatus) to move between fresh and salt water raises the question of whether manatees drink salt water. Water turnover rates were estimated in captive West Indian manatees using the deuterium oxide dilution technique. Rates were quantified in animals using four experimental treatments: (1) held in fresh water and fed lettuce (N=4), (2) held in salt water and fed lettuce (N=2), (3) acutely exposed to salt water and fed lettuce (N=4), and (4) chronically exposed to salt water with limited access to fresh water and fed sea grass (N=5). Animals held in fresh water had the highest turnover rates (145+/-12 ml kg-1 day-1) (mean +/- s.e.m.). Animals acutely exposed to salt water decreased their turnover rate significantly when moved into salt water (from 124+/-15 to 65+/-15 ml kg-1 day-1) and subsequently increased their turnover rate upon re-entry to fresh water (146+/-19 ml kg-1 day-1). Manatees chronically exposed to salt water had significantly lower turnover rates (21+/-3 ml kg-1 day-1) compared with animals held in salt water and fed lettuce (45+/-3 ml kg-1 day-1). Manatees chronically exposed to salt water and fed sea grass had very low turnover rates compared with manatees held in salt water and fed lettuce, which is consistent with a lack of mariposia. Manatees in fresh water drank large volumes of water, which may make them susceptible to hyponatremia if access to a source of Na+ is not provided.

Osmoregulation in wild and captive West Indian manatees (Trichechus manatus).

The ability of West Indian manatees (Trichechus manatus latirostris and Trichechus manatus manatus) to inhabit both freshwater and marine habitats presents an interesting model to study osmoregulation in sirenians. Blood samples were analyzed from manatees held in fresh- and saltwater and from wild animals captured in fresh-, brackish, and saltwater for concentrations of aldosterone, arginine vasopressin, plasma renin activity, Na+, K+, Cl-, and osmolality. Two separate experiments were also conducted on captive animals to evaluate osmoregulatory responses to acute saltwater exposure and freshwater deprivation. Spurious differences were observed in plasma electrolyte and osmolality among the captive and wild groups. Wild brackish water animals exhibited the highest vasopressin concentrations, while wild freshwater manatees had the highest aldosterone levels. A significant correlation between mean vasopressin and osmolality was demonstrated for captive and wild animals. When freshwater animals were acutely exposed to saltwater, osmolality, Na+, and Cl- increased 5.5%, 8.0%, and 14%, respectively, while aldosterone decreased 82.6%. Saltwater animals deprived of freshwater exhibited an almost twofold increase in aldosterone during the deprivation period and a fourfold decrease when freshwater was again provided. Within this group, osmolality increased significantly by 3.4% over the course of the study; however, electrolytes did not change. The lack of consistent differences in electrolyte and osmolality among wild and captive groups suggests that manatees are good osmoregulators regardless of the environment. The high aldosterone levels in wild freshwater animals may indicate a need to conserve Na+, while the high vasopressin levels in wild brackish-water manatees suggest an antidiuretic state to conserve water. Vasopressin levels appear to be osmotically mediated in manatees as in other mammals.

Morbilliviral epizootic in bottlenose dolphins of the Gulf of Mexico.

Morbillivirus infection was diagnosed in 35/67 bottlenose dolphins (Tursiops truncatus) from the Gulf of Mexico that stranded from October 1993 through April 1994 in Alabama, Mississippi, and Texas (USA) during periods of increased dolphin strandings in each of the 3 states. Diagnosis was based on histologic lesions, immunohistochemical demonstration of mobilliviral antigen, and detection of morbilliviral RNA by a reverse transcriptase polymerase chain reaction (RT-PCR) test performed on formalin-fixed, paraffin-embedded tissue (5 dolphins), on histologic lesions and detection of morbilliviral RNA by RT-PCR performed on formalin-fixed, paraffin-embedded tissue (1 dolphin), and on detection of morbilliviral RNA by RT-PCR performed on unfixed lung samples collected from carcasses with advanced postmortem autolysis (29 dolphins). Histologic lesions included proliferative interstitial pneumonia with syncytial cells and eosinophilic intranuclear and intracytoplasmic inclusion bodies, lymphoid depletion and syncytial cells with eosinophilic intranuclear inclusion bodies in lymph nodes, eosinophilic intracytoplasmic inclusion bodies in transitional epithelium of urinary bladder, and a syncytial cell with eosinophilic intranuclear inclusion bodies in epidermis. Concomitant pulmonary aspergillosis was diagnosed histologically in 4 dolphins. This is the 5th reported morbilliviral epizootic of aquatic mammals and the 2nd involving bottlenose dolphins in the United States.

Insulation and thermal balance of fasting harp and grey seal pups.

1. Harp and grey seal pups were examined during the post-weaning period to quantify their thermoregulatory abilities and thermal limits. 2. Deep body temperatures of harp seals (37.8 +/- 0.8 degrees C) were not significantly different from those of grey seals (38.9 +/- 0.4 degrees C). 3. As blubber depth declined during the fast, temperature gradients extended increasingly deeper into the muscle layer potentially decreasing heat loss. 4. Blubber conductivity (approximately 0.18 W/m/degrees C) did not vary regionally within an animal, or between animals or species. 5. Calculated lethal cold limits in air were between -85.4 degrees C and -116.1 degrees C, suggesting that fasting, weaned pups can easily cope with temperatures they would normally experience.

Sealpox in captive grey seals (Halichoerus grypus) and their handlers.

Histopathologic, ultrastructural, and negative-staining studies indicated that nodular lesions on the flippers, head, and necks of recently weaned, captive grey seals (Halichoerus grypus) were similar to sealpox lesions reported from several other species of seals. Virions associated with the nodules were characteristic of the parapoxvirus subgroup of pox viruses. Two of the three persons handling the seals developed nodular lesions similar to "milker's nodules," the characteristic lesion in persons infected with parapoxvirus. The clinical course of the parapoxvirus infection in both the grey seals and their handlers is described. It was concluded that although sealpox is transmissible to man, the mild clinical manifestations place it in the nuisance category of zoonotic diseases.