Tonic immobility (TI), also known as animal hypnosis, has been observed in a wide variety of taxa and reported in all vertebrate classes with the exception of Agnatha. To date, TI has been reported in six species of elasmobranchs. Preliminary results are presented here for five species of galeomorph sharks, one species of squalomorph shark, and six species of batoids. Tonic immobility was induced in the leopard shark, Triakis semifasciata; the whitetip reef shark, Triaenodon obesus; the blacktip reef shark, Carcharhinus melanopterus; the Caribbean reef shark, Carcharhinus perezi; the swellshark, Cephaloscyllium ventriosum; the California round ray, Urolophus halleri; the shovelnose guitarfish, Rhinobatos productus; the clearnose skate, Ruja eglanteria; the cownose ray, Rhinoptera bonasus; and the southern stingray, Dasyatis americana. The broadnose sevengill shark, Notorynchus cepedianus and the yellow stingray, Urolophus jamaicensis failed to exhibit the tonic immobility response, but only one individual of each species was tested. The average induction time ranged from 16.7 sec in the shovelnose guitarfish to 45.7 sec in the clearnose skate. Average duration times ranged from 34.3 sec in the clearnose skate to 274.0 sec in the Caribbean reef shark. Depending upon the species involved, TI has been used as an aid in a few husbandry and medical procedures in captive elasmobranches at the National Aquarium in Baltimore. These procedures have included gross examination, measuring lengths, tube feeding, and drawing blood via caudal venipuncture. Using tonic immobility during these procedures is beneficial as once induced, the subject's struggling is minimal and usually requires little restraint.

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Levels of reproductively-related steroids were determined in captive male sand tiger sharks, Carcharias taurus, maintained at two institutions: SeaWorld Adventure Park Orlando and the National Aquarium in Baltimore. Sexual conflicts were absent at the former, but were documented at the latter. Serum titers of 17beta-estradiol, progesterone, testosterone, and 5alpha-dihydrotestosterone were determined via radioimmunoassay in adult male sharks from 1988 to 2000. Sampling overlap between the two institutions occurred for 3 months of the year, but steroid concentrations were compared only for April due to the occurrence of sexual conflicts in the sharks at the National Aquarium in Baltimore in that month. For April, testosterone and dihydrotestosterone were significantly higher in the SeaWorld males, and progesterone was significantly higher in the National Aquarium in Baltimore males, while estradiol was not significantly different. Steroid levels were also determined from serial samples taken monthly over 17 months from three male sharks and one female shark at the National Aquarium in Baltimore in 2001-2002 and were compared with corresponding observed sexual conflicts. The steroid levels obtained showed distinct annual hormonal cycles in the male sharks and corroborated a biennial cycle for the single serially-sampled female shark. Furthermore, the steroid levels for individual males correlated with sexual conflicts as well as their position within the male dominance hierarchy. As this species is depleted in some regions globally, insight into the steroid profile of mature sand tiger sharks is important for a greater understanding of the relationship between their reproductive physiology and behavior, and may aid in captive management and reproduction.

Complete life history information is essential for effective population management, but little is known about the demographic characteristics of the southern stingray Dasyatis americana. We describe life history characteristics of southern stingrays maintained in captivity from birth to 13 years. Size (disc width [DW]) at maturity ranged from 48 to 52 cm in males and from 75 to 80 cm in females; age at maturity was 3-4 years in males and 5-6 years in females. Individual growth was described using three models: the Gompertz function, von Bertalanffy growth function (VBGF), and logistic function. Analyses of DW at age and weight at age indicated that females were significantly larger at birth and reached larger maximum sizes than males. Because of the ability of the VBGF to fit the observed growth and that of previously reported maximum sizes, we favor its use to describe individual growth dynamics for this species. Using this model, we estimated that for males (n ¼ 20), the asymptotic DW (DW ' ) was 67.4 cm, the von Bertalanffy growth coefficient (k) was 0.44 per year, and the predicted theoretical age at a DW of 0 cm (t 0 ) was À0.93 years. The corresponding estimates for females (n ¼ 15) were a DW ' of 150.9 cm, a kvalue of 0.11 per year, and a t 0 of À1.61 years. The oldest southern stingrays in the study were a 12-year-old male and a 13-year-old female, and estimates of longevity were 7.9 years for males and 31.5 years for females. The sex ratio of neonates (n ¼ 453) did not differ significantly from 1:1. The life history characteristics derived from captive specimens indicate that southern stingrays are similar to other dasyatids in terms of growth and age at maturity.

Historically, gymnurid rays have not done well in a captive environment. This report describes success in maintaining two specimens of the spiny butterfly ray, Gymnura altavela, in captivity. An aggressive husbandry protocol of tube feeding and force feeding maintained energy levels until the rays began to feed on their own. The rays used their pectoral fins to strike at food items, a behavior they may use in the wild to stun and capture prey. The first estimates of growth in captivity for any species of butterfly ray are given. Growth rates for the male averaged 0.063 mm/day (s.d.=0.030) and 10.253 g/day (s.d.=9.689), whereas growth rates for the female butterfly ray averaged 0.303 mm/day (s.d.=0.215) and 22.777 g/day (s.d.=15.2). Estimates of gross conversion efficiency (Kl) were calculated using the caloric values and known food intake. The estimates of Kl averaged 5.4% (s.d.=3.857) and 16.1% (s.d.=7.511) for the male and female, respectively, with a combined average of 10.8% (s.d.=7.95). These are the first estimates of Kl reported for any species of batoid using direct methods (growth rate and food intake). © 1996 Wiley‐Liss, Inc.