"Violent schizophrenia patients treated with fish oil (360mg DHA+540mg EPA) demonstrated a decrease in violence."
That was the primary conclusion arrived at in the study results by Yi Qiao and colleagues  suggesting that some aspects of nutrition may very well have implications for extremes of behaviour in the context of psychiatric diagnoses. The ClinicalTrials.gov entry for this study can be seen here.
DHA - Docosahexaenoic acid - and EPA - Eicosapentaenoic acid - are categorised as omega-3 fatty acids. In this research instance, Qiao et al divided up their "Fifty inpatients meeting ICD-10 criteria for schizophrenia" such that roughly half received a fish oil for 12 weeks and half received a placebo. I should add that this 'inpatient' group also scored significantly on the Modified Overt Aggression Scale (MOAS) at baseline.
Results: well, fish oil use did not seem to make any significant difference to some of the [positive and negative] signs and symptoms of schizophrenia compared with placebo use. But as per the opening sentence to this post, there did seem to be something significant to see when it came to follow-up of violent behaviour alongside the use of fish oils.
These are interesting findings. My first thoughts on reading the Qiao results harked back to previous work looking at the use of nutrition in the context of a prison population by Bernard Gesch and colleagues . That research concluded that: "Antisocial behaviour in prisons, including violence, are reduced by vitamins, minerals and essential fatty acids" where EPA and DHA were part of the supplement provided under "double-blind, placebo-controlled, randomised trial" conditions; albeit in smaller doses that those used by Qiao and colleagues.
The Qiao results are also not the first time that fish oil use for violence in the context of schizophrenia have been talked about in the peer-reviewed science domain . With the understanding that violence accompanying schizophrenia is probably going to be as complex as violence outside of schizophrenia, such promising results require some further replication and a little more data on possible hows-and-whys. The low cost, pretty favourable safety profile and reports of other potential health benefits associated with fish oil use however, suggest that such an intervention could easily be incorporated into treatment plan for many people fitting a similar profile to those described by Qiao and colleagues.
 Qiao Y. et al. Effects of Omega-3 in the treatment of violent schizophrenia patients. Schizophr Res. 2017 Aug 19. pii: S0920-9964(17)30501-7.
 Gesch CB. et al. Influence of supplementary vitamins, minerals and essential fatty acids on the antisocial behaviour of young adult prisoners. Randomised, placebo-controlled trial. Br J Psychiatry. 2002 Jul;181:22-8.
 Légaré N. et al. Omega-3 and violence in schizophrenia. Schizophrenia Res. 2007; 96: 269.