Embryo development timeline, mating behavior and reproductive parameters in Sympterygia acuta (Arhynchobatidae), a common coastal skate species from the Southwestern Atlantic

GABBANELLI, V.; VAZQUEZ, D. M.; DÍAZ DE ASTARLOA J. M.; RODRIGUEZ, F.; MABRAGAÑA E.

Conferencia; Sharks International Conference; 2018

Studies in captivity on chondrichthyans allow toinvestigate in detail embryonic development andother aspects of reproduction. Skates are oviparousand their egg cases can be easily maintained underlaboratory conditions. Of the nine skate speciesinhabiting coastal waters from the SouthwestAtlantic, embryo development timeline has beenperformed only in Sympterygia bonapartii. Here, wedescribe for the rst time the complete embryonicdevelopment with a timetable of S. acuta, a coastalspecies with a marked seasonal reproductive cycle.Other features such as mating behavior, incubationperiod, size at hatching and sex proportion arealso provided, through the study under controlledconditions of captivity. ree mature females of S.acuta were maintained in a 20000-liter tank withaerated seawater in a closed system, at Mar del PlataAquarium. Specimens were kept trying to mimicnatural conditions (11-21°C, natural photoperiod)from September 19th to December 22nd, 2017,butone female died by November 14th. A total of 53egg cases were deposited in a period of 80 days. Eggcases were collected after deposition and placedin oating baskets in the same tank. Four maturemales were also present in the tank. Embryonic developmentwas described in detail analyzing a totalof 42 embryos sampled every 14 days. e rst halfof the embryonic development shows the appearanceof the embryonic axis and cranial structures,development and growth of gill laments, presenceof dorsal ns, growth of pectoral and pelvic ns withdi erentiation into claspers and a pulsatile heart.After 70 days until hatching, the embryo acquiresthe typical batoid disc, mouth and nares becomeneonatal, gill laments are resorbed and spiraclesbegin to pump bringing oxygenated water into theinternal gills, spinulation, epidermal and eye pigmentationare set, and yolk is being absorbed. Afterhatching, the embryo is fully pigmentated, breathesnormally, has reabsorbed most of the yolk, and isable to swim independently. Incubation periodat 11-21°C was between 89-108 days (mean±S.D.,94.2±5.9 days). Size at hatching ranged from 87-94mm (mean±S.D., 90±2.5 mm total length), sex ratio(F:M) was about 1-1.1 and viability of egg cases was~ 98%. Considering the time period shared by thethree egg-depositing females (50 days), estimatedrelative fecundity was 13 eggs/female. Copulationevents recorded by video are also described. Sympterygiaacuta is a good model to carry out studies incaptivity on skates, given its rapid adaptability andgood reproductive performance.