ASPECTS OF EMBRYONIC DEVELOPMENT IN TWO SOUTHWEST ATLANTIC GADI-FORM FISH: TADPOLE CODLING, SALILOTA AUSTRALIS (MORIDAE), AND SOUTHERN BLUE WHITING, MICROMESISTIUS AUSTRALIS (GADIDAE)

Tadpole codling, Salilota australis (Gunther, 1878), (known also as red cod) and southern blue whiting, Micromesistius australis Norman, 1937, are two commercially important species, which spawning grounds are situated in the Falkland waters. Nothing is known about duration of the embryonic development in these fish, whereas these data are necessary to study life cycle strategies as well as for stock management. Because of this, experiments with artificial egg fertilisation were carried out onboard a research boat that was the only way to obtain such an information.Materials and Methods. Eggs from each species were taken from running females captured on their spawning grounds and then fertilised. Egg samples were collected every 6 hours and stage of embryonic development was assigned using a dissecting microscope.Results. Tadpole codling eggs are of 1.20-1.55 mm, with an oil globule of 0.29-0.33 mm, incubation takes between 140-150 h at 6-8.5°C, 40-45 degree-days. Larval size at hatching is ca 2.9 mm TL. Blue whiting eggs are of 1.40-1.55 mm with no oil globule. Development takes from 150 h at a mean temperature of 7.15°C to 200 h at between 5.5 and 6°C, 45-50 degree-days. Larval size at hatching is 2.8-3.0 mm.Conclusion. Duration of embryonic development for commercial southwest Atlantic gadiform fish, tadpole codling, Salilota australis, and southern blue whiting, Micromesistius australis, is documented for the first time. It allows to draw some conclusions about possible mortality during this ontogenetic stage (assuming that daily rates are similar to those in other similar species) and to hypothesise about possible egg transport by currents and interannual spawning groundsʹ variability.