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The American Elasmobranch Society


Abstracts of AES Scientific Papers
American Elasmobranch Society 1997 Annual Meeting
Seattle, Washington
ABSTRACTS - Part 4: Neal through Stoops
Neal, Ashley E., Wourms, John P.

 Maternal-Embryonic Transfer of IgM via Eggs in Gingymostoma cirratum.

Immunoglobulin M (Ig M) is the chief circulating antibody in adult elasmobranchs. Although its presence has also been established in neonates and unborn pups, its origin is not conclusively known. There are two possibilities: de novo synthesis and maternal transfer. Maternal embryonic transfer of passive immunity via Ig M occurs in oviparous and viviparous teleosts. In viviparous elasmobranchs, placental transfer of IgM is questionable because the intervening collagenous egg envelope acts as a macromolecular sieve. Transfer of IgM has not been studied in aplacental vivparous elasmobranchs, oviparous species, or the eggs of either. Since IgM transfer and storage occurs in avian eggs, we hypothesized that the macrolecithal egg of elasmobranchs is also a likely vehicle for IgM storage and transfer. Ovaries and individual eggs of Gingymostoma cirratum were collected and analyzed for IgM. Eggs were freed of investing membranes and the yolk was processed using a chloroform/PEG procedure to isolate immunoglobulins. Gel electrophoresis of the Ig fraction revealed a protein banding pattern consistent with the molecular weights of IgM heavy and light chains. ELISA and Western blot assays indicated a strong cross-reactivity with antibodies against stingray IgM. We conclude that unfertilized eggs contain IgM transferred from the maternal serum during oogenesis.

Newton, Mary C.

 Jaws meets Star Trek: the use of relative warps analysis int he study of shape-variation in the teeth of the white shark, Carcharondon carcharias.

The study of variation in shape has long been restricted to the use of either descriptive language or the analysis of linear measurements through multivariate statistics. Geometric morphometrics is a new technique that can capture shape-variation more completely than either of the previous techniques. Relative warps analysis, a type of geometric morphometrics, was used to analyze shape-variation with a population of fossil and modern teeth from the adult white shark, Carcharodon carcharias. Relative warps analysis successfully separates the categories of modern teeth in the upper jaw, but does not separate the lower jaw categories from the upper jaw categories very well. No difference was found between the three-million-year-old (MY) fossil teeth and the modern teeth, but the teeth from five million years ago are distinctly different. All categories of 5 MY teeth are narrower and have large terminal serrations at the base of one or both margins. The intermediate tooth is reversed in the 5 MY set, indicating a possible change in the morphology of the upper jaw.

Piermarini, Peter, M., Evans, David, H.

 Osmoregulation of the Atlantic Stingray (Dasyatis sabina) in the freshwater Lake Jessup of the St. Johns River, FL.

Dasyatis sabina is one of the few euryhaline elasmobranchs that can live and reproduce in fresh water (FW). To date, no lab studies have investigated the osmoregulation of such an elasmobranch in FW. The goals of this study were to describe the osmoregulation of D. sabina in the FW Lake Jessup of the St. Johns River, FL, and determine their ability to acclimate to sea water (SW). Plasma samples were collected from FW D.sabina captured in Lake Jessup and individuals acclimated to 100% SW in the lab. Analyses indicated that FW D. sabina hyper-osmoregulate with mean plasma Na+, Cl-, K+, Ca2+, and urea concentrations of 208.96, 205.91, 5.37, 4.10, and 186.26 mmol/l, respectively. D. sabina survived the transition to 100% SW; they hypo-osmoregulate with mean plasma Na+, Cl-, K+, Ca2+, and urea concentrations of 325.56, 306.26, 5.27, 5.55, and 325.79 mmol/l, respectively. Mean total plasma osmotic concentration increased from 608.80 mOsm/kg in FW to 949.81 mOsm/kg in 100% SW. These data suggest that D. sabina of Lake Jessup have not lost their ability to retain urea and are truly euryhaline elasmobranchs.

Rasmussen, L.E.L., Luer, Carl A.

 Correlates of serum hormone concentrations and reproductive events throughout the year in captive and wild caught clearnose skates, Raja eglanteria.

This long term investigation of serum steroid reproductive hormones in the clearnose skate, Raja eglanteria, demonstrates interesting correlations between changing hormonal concentrations and reproductive events. Animals were sampled both individually (78 females and 20 males) and serially (15 females). Serum estradiol was detected throughout the year with significant elevations occurring during October and November when the ovarian follicles begin to develop and January and February when maximum mating occurs and egg laying begins. During this latter period similar, even more pronounced elevations occurred in serum testosterone and dihydrotestosterone concentrations. Subdividing the egg laying process into 5 stages defined by the position of palpable eggs revealed that 17 Beta estradiol levels were highest when the eggs were in the nidamental gland (stage 2) or uterus (stage 3), and testosterone and dihydrotestosterone concentrations were maximal when eggs were in the uterus or cloaca (stage 4). Conversely, progesterone levels were significantly elevated immediately after the egg laying (stage 5). These results strongly implicate hormonal control over the egg laying process, including observed periodic synchronies between estrogens and androgens. Initial studies to assess relative hormone concentrations and syntheses along the reproductive tract of females and within reproductively-related secretions of males have begun to provide information on sites of hormone production for this species.

Shivji, Mahmood S., Stanhope, Michael J., Rogers, Scott 0.

 Group I introns ("spintrons") are present in shark nuclear ribosomal DNA internal transcribed spacers.

Group I introns are a family of sequence elements that interrupt genes, and are characterized by conserved secondary structure and short sequence regions essential for splicing. Although common in some lower eukaryotes, group I introns have thus far been conspicuously absent in metazoans. We report here the first observation of group I introns from animal nuclear genomes. These introns are present in diverse shark lineages, and are novel also because they interrupt a non-genic region (the ribosomal DNA internal transcribed spacer 2), rather than a genic region as in other organisms. In light of this unusual location, we refer to these elements as "spintrons" (for spacer introns) to reflect a previously undocumented spacer insertion. The presence of spintrons in the ITS2 likely has major implications for currently known mechanisms of precursor ribosomal RNA transcript processing. The spintrons in the nine shark species (representing four orders) examined here share a common insertion site in the ITS2. This observation, together with results from phylogenetic analyses of the spintron and ITS2 spacer sequences, suggests that a spintron was present in the common ancestor of sharks, and has likely been inherited vertically over at least 400 million years of shark evolution.

Silva, Alexandre

 Some results on the blue shark (Prionae glauca) in Azorean waters from a research cruise by the R/V Arquipélago.

This paper summarizes some results on the blue shark based on data from a large pelagics cruise survey carried out with the R/V Arquipélago in Azorean waters during the Autumn of 1993 and the Spring of 1994. Blue shark CPUE data for the Azores, by geographical area and season, and length frequency distributions are presented. CPUE ranged from 0.2 to 36.2 blue sharks/100 hooks, with the highest values recorded for the oceanic area during the spring season. A strong increase in CPUE was detected from the autumn to the spring season. Length frequency samples collected during the autumn and spring seasons revealed a complex seasonal segregation pattern for the blue shark in Azorean waters. While the autumn sample showed a high incidence of juveniles and sub-adults, in approximately equal proportions, and an equal sex-ratio, the spring sample was clearly dominated by the juvenile segment and by females. This information suggests that the area around the Azores represents an important nursery ground for blue sharks in the Atlantic during the spring season. The implications of such a nursery area is discussed within the global Atlantic context.

Simpfendorfer, Colin

 Results of a tagging study on juvenile dusky sharks (Carcharhinus obscurus) in south-western Australia.

Juvenile dusky sharks, Carcharhinus obscurus, are an important component of the shark fishery in south-western Australia. to investigate the dynamics of juvenile C. obscurus in relation to the fishery, a tagging study was undertaken. 2199 juvenile C. obscurus, mostly 0+ individuals, were tagged with Jumbo Rototags from commercial gillnet vessels between March 1994 and June 1996. 517 of these animals were double tagged with metal headed dart tags. At the 1st of March 1997, 391 recaptures had been reported, most by commercial gillnet fishers, but also commercial line fishers and recreational fishers. Release and recapture locations show that juvenile C. obscurus can move long distances, with 23 individuals moving over 500 km. The majority of recaptures, however, were within 100 km of the release point. Movement patterns of juvenile C. obscurus are discussed. Estimates of growth rates of juvenile C. obscurus, based on the size at release and recapture, were 8.9 cm year-1. Analysis of the return of double tagged individuals indicated that the tag shedding rate of Jumbo Rototags was 0.0385 year-1 and for metal headed dart tags 0.346 year-1. Tag recapture rates by commercial gillnet fishers, corrected for tag log and non-reporting, indicated that they catch between 20 and 28% of C. obscurus born each year.

Stoops, Gary L., Jr., Dehart, Andrew H.

 Husbandry observations and treatment of fungal infection in tiger shark, Galeocerdo cuvier.

Tiger sharks, Galeocerdo cuvier, are rarely displayed in public aquariums, and little is known about their behavior and health in the captive environment. Omaha's Henry Doorly Zoo displayed this species from March 15, 1995 to August 24, 1996. The tiger shark arrived at an estimated 35 kg body weight, and was about 152 cm TL. The initial diet averaged 3.4 kg per week. The body weight increased steadily, and at death the shark was estimated at 100 kg and measured 241 cm TL. At the peak of its appetite the shark was eating 7.6 kg and her total weight was probably much higher. Behaviorally the shark swam the perimeter of the exhibit, which led to skin abrasion problems. Most of the abrasions were successfully treated with enrofloxacin, but a secondary fungal infection was diagnosed and treated with ketaconazol. The ketaconazol treatment appeared to improve the fungal infection externally. At the time of the shark's decline a possible Vibrio infection was suspected due to equilibrium problems and was treated with Florfenicol. Necropsy results showed sever multifocal ulcerative gastritis and large numbers of fungal hyphae. The purpose of this presentation is to exchange ideas, and share information about the captive care of Galeocerdo cuvier.