Introduction

1. Captive Biology of Pelagic Stingrays, Dasyatis (Pteroplatytrygon) violacea in the First Year Ann Coleman, Husbandry Division, Monterey Bay Aquarium, California, USA Randy Wilder Discussion Both growth and feeding data collected in the first 8 months appear to be as expected when compared to pelagic stingray growth from the Mollet et al, 2002 paper. Both pelagic stingray pups grew at the same rate of 30 cm/yr and 2.5 kg/yr, which presents some interesting questions. Mollet et al, 2002, determined that males are thought to mature at around 35–40 cm in the wild and females at 45–55 cm. This indicates that both pups will reach the size for maturity within one year. This may mean that in captive situations, captive-born rays could reach sexual maturity before 2 years of age. In the future, we will start collecting data on clasper length for the male. We will also be looking for an increase in growth rate for the female in the next year, as well as any mating activity. Since the pups are getting larger, future measurements will be done using the anesthesia MS-222 for more accurate measurements. This study will continue, and additional data will be collected on the overall growth of neonate pelagic stingrays in their first two years. References Mollet, H.F. 2002. Distribution of Pelagic stingray, Dasyatis violacea, off California, Central America, and worldwide. Marine and Freshwater Research 53, 525–30. Mollet, H.F., Ezcurra, J.M., and O’Sullivan, J.B. 2002. Captive biology of the pelagic stingray, Dasyatis violacea. Marine and Freshwater Research 53, 531–41. Acknowledgments I would like to thank Henry Mollet for all his help with compiling the data and providing background information on pelagic stingrays; Freya Singer, Jonelle Verdugo, Scott Reid, and Manny Ezcurra for their help with feedings and measurements; and Christina J. Slager for her editorial assistance. For Further Information Please contact acoleman@mbayaq.org More information on this and related projects can be obtained at homepage.mac.com/mollet/ Introduction The pelagic stingray, Dasyatis (Pteroplatytrygon) violacea is a common ray species found in aquaria worldwide. It is a species that has been displayed for over a hundred years, beginning in Naples, Italy. However, there has been little data collected on the growth and feeding of this species in a captive environment, especially in the neonate stage of 0–2 years. This is due to the low reproductive success and low pup survival in aquaria (Mollet et al, 2002). Table 1 shows all known pelagic stingray reproductive success in aquaria. Monterey Bay Aquarium (MBA) had its first successful pelagic stingray births on 1 March 2004. The litter of two, one female and one male, provided the opportunity for an age, growth, and feeding study (Fig. 1). The results presented here represent the first eight months of a two-year study. It includes disc width (DW) and mass versus age, and mean weekly amounts fed for both rays. Results The growth data for the 2 pups showed a large growth rate of 30 cm/yr and 2.5 kg/yr for both sexes within the first 8 months (Fig. 4). Typically, females grow to a larger size than males (Mollet et al, 2002). This was not found to occur within the first 8 months of the neonate stage. The pups had an initial DW of 18.5–19.5 cm and mass of 0.23 kg. At 8 months, they reached a DW of 38–39 cm and a mass of 1.7–2.0 kg. As the rays aged, the mean weekly amounts of food in grams per day increased, however mean weekly food intake as a % Body Mass decreased slightly (Fig. 5). The conversion factor for the neonate pelagic stingrays is based on energy values for squid and lemon sharks (Fig. 6). Materials and Methods During a collecting trip on the NOAA research vessel, R/V David StarrJordan, in June 2003, 2 female pelagic stingrays and 1 male were collected and brought back to the MBA. All three were kept in a holding tank together where mating was observed and where fertilization most likely occurred. A litter of 2 pups, 1 male and 1 female were born on 1 March 2004 in the parent holding tank. Holding tank temperature was kept at 20C (68F). The pups were moved to a separate 4’x 8’ (27.174foot2) holding tank kept at a higher temperature of 23.8C (75F). Both rays were held in the same 4’x 8’ holding tank for the first 7 months then transferred to a larger cylindrical tank (10’ diameter, 78.54foot2) kept at the same temperature. The male is easily distinguishable from the female due to the presence of claspers and a white birthmark on the dorsal side. Measurements were conducted using the metric system so DW was measured in centimeters and weight was measured in grams. Once a month (every 4 weeks after initial measurement) each ray’s DW was measured accurately by hand using a measuring tape over the curve of the dorsal side from widest wing-tip to wing-tip. The first measurement was taken at one-week-old after the rays had started to feed. Weight was measured once a month (every 4 weeks after initial measurement) by placing each ray in a large tub of seawater and then subtracting the weight of the tub and water. The first weight and measurement was taken at 1-week-old after the rays had started to feed. Both pups showed no signs of stress after initial measurements, so accurately weighing and measuring once a month was considered feasible without anesthesia (Fig. 2). Since the rays are easily identifiable from one another, the feeding study was conducted by weighing out individual amounts of squid for each ray and feeding to satiation on a daily basis. Feeding was done by hand at the side of the tank. At 3 months, a feeding target was introduced to this same area to start training the pups to come to a feeding station when moved to a larger tank (Fig. 3). A B Fig. 4. Growth of captive pelagic stingrays from 1 Mar –1 Nov 2004. (A) DW, (B) Mass. C D Fig. 1. Pelagic stingrays of study. Female on left. Table 1. Pelagic Stingray Reproductive Success and Pup Survival in Captivity Fig. 5. Food intake of captive pelagic stingrays. Mean weekly food amounts expressed in (C) g/day and (D)%BM/day. Fig. 3. Feeding ray. Note target used for station training on right side of tank Fig. 2. Taking DW measurement of female (Reference for aquaria other than MBA from H. Mollet, personal communication September 2004.) Fig. 6. Conversion factor for the rays.