One study involved 80 young people aged 13 to 25 with early symptoms of schizophrenia. Half were randomly assigned to take fish oil tablets for 3 months and the other half were given a placebo for 3 months. The researchers followed the subjects for seven years and found that only 10 percent of those taking fish oil tablets developed schizophrenia, compared with 40 percent of those taking a placebo. 
The age span of the subjects is relatively large. Someone may have been an adult rather than a teenager when the experiment began.
 the researchers concluded that taking fish oil tablets may help prevent schizophrenia in adolescents.