Eyewitness accounts from those who have been fishing in the Gulf for decades,  alongside reports from scientists who have studied Gulf fish populations pre- and post-spill give a reasonable indicator that the abnormalities are tied to  the release of chemicals in the oil, or the controversial dispersant used in an  attempt to clear the enormous spill. 
Dr.  Jim Cowan of Louisiana State University’s Department of Oceanography and  Coastal Sciences told 
Al  Jazeera that prior to 2010, the NOAA reported around one tenth of one  percent of fish in the area presented with sores, “but nothing like we’ve seen  with these secondary infections and at this high of rate since the spill.”
Polycyclic aromatic hydrocarbons (PAHs), a volatile compound found in crude  oil, have been detected in fish and crab populations, as well as in marshlands  around the coast. 
OnEarth describes  that PAHs have been linked to cancer, birth defects, neurological impacts, and  liver disease. Dixon believes that the PAH causes damage to the sealife, leaving  them vulnerable to microbial infections, resulting in lesions, and notes that  similar symptoms were reported in fish following Exxon Valdez.
The dispersant, meanwhile, contains solvents, known to cause an array of  health problems from skin and respiratory irritation to cardiovascular and  neurotoxic effects. 
Al  Jazeera speculates “the dispersant is also known to be mutagenic, a  disturbing fact that could be evidenced in the  seafood deformities. Shrimp, for  example, have a life-cycle short enough  that two to three generations have  existed since BP’s disaster began,  giving the chemicals time to enter the  genome,” and from there we see shrimp without eye sockets — a view 
reflected  by Scott Eustis of the 
Gulf Restoration  Network. 
Read more:  
Eyeless Shrimp and Deformed Crabs a Serious Problem 2 Years After Gulf Oil Spill | Inhabitat - Sustainable Design Innovation, Eco Architecture, Green Building