Do hypoxic waters affect reproductive biology of male bearded goby?

Bearded goby (Sufflogobius bibarbatus) is a key species in the northern Benguela Upwelling Ecosystem, and it tolerates extremely low levels of oxygen. Until now little has been known about how its reproduction is affected by these harsh living conditions. This paper in Journal of Sea Research presents methods developments and their application for studies of reproductive biology and the distribution patterns of alternative reproductive tactics of male bearded goby across the continental shelf off Namibia. 

For the first time for male fish, histology and stereology was applied to validate a macroscopic maturity key. The approach is to estimate volume fraction of the different stages of spermatogenesis using “Delesse principle”, a method that previously only has been used for advanced oocyte estimation for female teleost fish. Histological analysis confirmed that  the macroscopic scale was good and that it could be used to examine the prevalence of territorial and sneaker tactics of male bearded goby (S. bibarbatus). Territorial males had large seminal vesicles (SV) and small testes, while the sneaker tactic had small SV and large testes. A third, numerous, but unclassified group of male gobies, had intermediate sized testes and SV. These could not be allocated to any clear reproductive tactic; but the overall data suggest that the most likely explanation is that most of these represented a group of skip-spawning males that initially started to produce sperm, but then omitted spawning until the following reproductive season.

Mature S. bibarbatus males were not evenly distributed over the continental shelf of northern Benguela. Low oxygen levels were the most important factor limiting spawning activity in territorial males. The data suggested the existence of a spawning site on the outer central Namibian shelf where the bottom water is hypoxic (oxygen saturation of 6.2 – 6.7 %) while the anoxic middle shelf area (oxygen saturation of 1.7 – 2.9 %) appeared to show too low oxygen levels for spawning to take place. It is concluded that significant parts of this large shelf area appear unsuited for successful reproduction of the bearded goby, in particular for nest building by the territorials.

Reference:

Seivåg, M. L., A. G. V. Salvanes, A. C. Utne-Palm, and O. S. Kjesbu. 2016. Reproductive tactics of male bearded goby (Sufflogobius bibarbatus) in anoxic and hypoxic waters. Journal of Sea Research 109:29–41. doi:10.1016/j.seares.2016.01.002. 

Free access link (valid until March 6, 2016) 

See also:

Salvanes, A. G. V., A. C. Utne-Palm, B. Currie, and V. A. Braithwaite. 2011. Behavioural and physiological adaptations of the bearded goby, a key fish species of the extreme environment of the northern Benguela upwelling. Marine Ecology Progress Series 425:193–202. doi: 10.3354/meps08998. Open access!