ABSTRACT
Sturgeons and paddlefishes of the order Acipenseriformes are an ancient group of fishes that exclusively inhabit the Northern Hemisphere. Several species are used in aquaculture programs and farmed for their roe sold as caviar and their high quality boneless meat. However, some species are critically threatened or endangered for reasons including destruction of habitat and spawning grounds, overexploitation of stocks and uncontrolled poaching and require restoration efforts. The acipenseriform species that have been studied share a number of characteristics especially concerning their spermatozoa and composition of seminal fluid. Distinctly different from the general morphology of teleost spermatozoa, sturgeon and paddlefish spermatozoa have long cylindrical heads topped with functioning acrosomes, well-defined midpieces with several mitochondria and flagella with fin-like extensions on both sides of the posterior end of the tails [1,2]. Osmolality/osmolarity of sturgeon and paddlefish seminal fluid is 60-100 mOsm/kg which is significantly lower than that of teleost fish (260-300 mOsm/kg) [3]. Lower osmotic shock occurs when released into freshwater and is probably the reason why these spermatozoa swim for a longer period of time (4-6 minutes) than spermatozoa of other freshwater teleosts (less than a minute). Concentration of acipenseriform sperm, typically up to 1-1.5 billion spermatozoa per ml, is also much lower than that of teleosts [2,3,4].
