A test of the carbonic anhydrase-dependent model for emergence and hatching in the brine shrimp Artemia franciscana (Kellogg, 1906) (Branchiopoda: Anostraca)

Heavy metals and organic pollutants are present in commercially harvested embryos of the brine shrimp, Artemia franciscana (Kellogg, 1906) from the Great Salt Lake, UT, USA, which raises questions about the long-term viability of this commercially important population. More information about hatching physiology is required to address this toxicological question. Bicarbonate deficiency, low culture density, and heavy metals all induce similar aberrant morphology during early development of the post-diapause embryo. Previous studies suggest that the common link among these treatments is a failure in the physiological mechanisms that facilitate emergence from the first embryonic cuticle. It is possible that bicarbonate deprivation and heavy metal exposure have similar effects on emergence and hatching because they target a single enzyme. The present work tests the long-standing hypothesis that a carbonic anhydrase drives ion transport required for the final phase of osmotic swelling during emergence and hatching. Data presented provide the first evidence of an acetazolamide-sensitive carbonic anhydrase in developing embryos, but do not support the hypothesis that a carbonic anhydrase is required to generate osmotic pressure for emergence or hatching. Acetazolamide treatment increases hatching of E2-Oval prenauplii under culture conditions that promote the development of aberrant emergence morphology. Progression through the E1 and E2 emergence stages is also accelerated by acetazolamide in a concentration-dependent manner when embryos are cultured under conditions that promote normal development, emergence, and hatching. These results are contrary to predictions of the carbonic anhydrase-dependent hatching model proposed by Trotman (1991), and indicate that a carbonic anhydrase is not the common target of diverse treatments known to impair emergence and/or hatching. Standardized culture conditions and alternative physiological targets for future studies are discussed.