Low oxygen levels recorded along the 
Gulf Coast of 
North America have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning.
 In a study of the Gulf 
killifish by the 
Southeastern Louisiana University  done in three bays along the Gulf Coast, fish living in bays where the  oxygen levels in the water dropped to 1 to 2 parts per million (ppm) for  three or more hours per day were found to have smaller 
reproductive organs.  The male gonads were 34% to 50% as large as males of similar size in  bays where the oxygen levels were normal (6 to 8 ppm). Females were  found to have ovaries that were half as large as those in normal oxygen  levels. The number of eggs in females living in hypoxic waters were only  one-seventh the number of eggs in fish living in normal oxygen levels.  (Landry, et al., 2004)
 Fish raised in laboratory-created hypoxic conditions showed extremely low 
sex hormone concentrations and increased elevation of activity in two 
genes triggered by the hypoxia-inductile factor (HIF) 
protein.  Under hypoxic conditions, HIF pairs with another protein, ARNT. The two  then bind to DNA in cells, activating genes in those cells.
 Under normal oxygen conditions, ARNT combines with estrogen to activate genes. Hypoxic cells 
in vitro  did not react to estrogen placed in the tube. HIF appears to render  ARNT unavailable to interact with estrogen, providing a mechanism by  which hypoxic conditions alter reproduction in fish. (Johanning, et al.,  2004)
 It might be expected that fish would flee this potential suffocation,  but they are often quickly rendered unconscious and doomed. Slow moving  bottom-dwelling creatures like clams, lobsters and oysters are unable  to escape. All colonial animals are extinguished. The normal  re-mineralization and recycling that occurs among 
benthic life-forms is stifled.