Viruses do carry their own DNA, some carry RNA instead. M13, one of the most primitive "life forms" known to science, is a filamentous phage, meaning it can only infect/use bacteria to replicate itself. It is extensively used and manipulated in molecular biology laboratories. So, the fish need not worry. These scientists had to integrate the system with a gel matrix to maintain stability and efficiency which i doubt would hold up in sea water. Something this complex would have to be controlled and monitored extensively and I doubt would lead to some disastrous chain reaction.