Arrow, any fish that's get harvested after 4 years has an endangerment of heavy metals toxicity level, which include trouts, BG, tilapia, etc.. However, it's all about the water that the species thrive in. Don't be too worry about mercury, unless, you know of the lab analytical results come back high for mercury, or any heavy metal. Mercury can be natural from existing in the soil, as well as being deposited from dust settling into the water via atmospheric deposition (primary cause is from nearby mining operation and China..yep..China).

You may be weary about DDT, or any other pesticide/herbicide from the local usages for vegetation/pests management.

As Bill mentioned, if your water can sustain a good quantity of BG, HBG, GSF, mixed in with a bit of bass for control, these will be great for your heart and liver. Trout tossed into the mix will be a lively dietary contribution.

At the same time, since you are concerned about human health, if you're feeding them pellets, make sure the pellets are not heavily reinforced with corn base. Corn will promote fish growth, but also a health factor for human consuming the fish. Corn based product decrease the omega 3 (the good) of the fish, and increase the omega 6 (the bad). This is why I encourage those who raise their fish for consumption with partial supplementation of krill based food source. Expensive, but extremely healthy for both fish and human as we climb the food pyramid. If a pond is close to or near +/-400ft of sea level, harvest and promote grass shrimps in the water body. The presence of the grass shrimp will be an invaluable resource for growth, nutrition, and vitality of the biota.

Leo

* Knowledge and experience yield wisdom. Sharing wisdom expand the generations with crucial knowledge. Unshared wisdom is worth nothing more than rotting manure.