"Too much fish oil can suppress immune function and might just result in too much omega 3s circulating in your blood." Where have you heard that? Sounds, interesting
3.5g fish oil for 12 weeks (otherwise healthy 50-70yrs) has failed to significantly influence IL-2[386] and failed to influence with 2g daily in persons with isolated hypertriglyceridemia.[387] However, 18g of fish oil (2,754g EPA and 1854mg DHA) daily in otherwise healthy youth has been noted to reduce secretion of IL-2 in stimulated PBMCs by a variable 23-52%[374] and in type II diabetics, IL-2 has been reduced following fish oil supplementation (1,548mg EPA and 338mg DHA for 8 weeks) by 17.1%.[388] The efficacy of fish oil in suppressing T-cell activity and IL-2 does not appear to depend on disease state.
"The sIL-2R has been shown to be present in the culture supernatants of activated MNCs as well as in normal sera and, in higher amounts, in sera from subjects affected by several diseases including neoplastic, infectious and autoimmune ones, and in sera from transplanted patients suffering allograft rejection. " (
http://www.ncbi.nlm....les/PMC2365387/)
In some cases lowering the IL-2 with chronic fishoil supplementation could be seen as a good thing because the body is much more complex than any boost in the immune system being good and any decrease being bad. And, even if a normal person took a chronic dose enough to effect the IL-2 receptor it still is shown to be well tolerated.
A elevated IL-2 is associated with a immunology abnormality. So, yes fish oil in chronic doses can "decrease the immune system" but the part of the immune system it is decreasing is not what we think of when we think a high immune system is a good thing. Rather, its decrease in IL-2 could be seen maybe as more of a regulatory or modulating effect. And, it is still unclear if the decrease from extreme doses in healthy persons would even have any relevant effects to them.
Having too much omega 3s circulating in your blood is probably not possible. Humans used to live on a 1:1:2 ratio of omega 3:6:9. Also fishoil isn't even 1000% omega 3's anyway. My 1000mg fishoil only supplies 250mg of omega threes and a 2000 calorie diet eating the ideal omega 3:6:9 ratio that caveman ate one would be consuming 55,000mg of omega 3s a day or over 200 fish oil capsels and while they would probably have side effects it would still not be from too much omega 3s circulating in your blood.
Fishoil has omega3s however omega threes are not = fishoil