The forum name and description should indicate what is on-topic (beyond what the rules forbid/describe). For instance, in the watermelon forum, you can talk about pretty much anything related to watermelon (Citrullus lanatus). For plant and animal forums, the description often describes the binomial name of the species at hand.
In the Cow forum (as another example), you can discuss pretty much anything related to cows. That includes raising cows, breeding cows, herding cows, milking cows, milk, cow leather, cow cheese, cow butter, beef, vaccinating cows, cow manure, activism against eating cows, alternatives to specific cow products (but yes, you have to mention those cow products for the post to be in the cow forum), imitation cow products, cow science, humanitarian efforts relating to cows, cow pets, science articles involving cows, cow art, cow decorations, cow costumes, cow T-shirts, cow music, cow encounters, cow diseases, cow pastures, cow barns, recipes that focus on cow products, etc.
In the Asian Swamp Eel forum, as another example, you might discuss a similar array of things. You might also discuss them as an invasive species, or you might talk about their survival traits.
Not every forum on this site is intended to be about something edible. It is also not always stated whether or not the thing is edible. Do your own research, even where it is stated (don’t take this site’s word for it).
Posts promoting hunting, fishing, and/or foraging in a fashion that could easily contribute to the decline of the hunted/fished/foraged species are off-topic.
Posts directly promoting the genocide of a species are off-topic.
Posts promoting the intentional extirpation of species are off-topic (whether or not they are invasive species).
Location: SW Idaho, USA
USDA hardiness zone: 6
Elevation: 2,260 feet Profile post