I would like to fill a medium sized fish (rockfish) with a pesto like marinade and broil it. Could I use very slim chicken wire to wrap a couple coils around the fish to keep the filling in or should I use something else? Toothpicks won't do because the skin at the edges isn't firm to hold. Any downside to using wire?
I would not expect chicken wire to be food-safe.
According to the FDA, to be considered food-safe, a material must meet several conditions:
It must not allow the migration of “deleterious substances or impart colors, odors, or tastes” to food
Be “durable, corrosion-resistant, and nonabsorbent”
Possess sufficient “weight and thickness to withstand repeated warewashing”
Be “finished to have a smooth, easily cleanable surface”
Have resistance to “pitting chipping crazing, scratching, scoring, distortion, and decomposition”
Now a lot of that might not be much a concern if you only plan to use it once, but still, I'd recommend spending a few extra pennies for stainless steel or aluminum wire, which you should be able to find in any large hardware or home improvement store. The link above goes on to say specifically that grade 304 and 316 stainless steel and aluminum are food safe.
Another option that might work for you is a grilling basket.
You could use food grade Transglutaminase (aka Meat Glue). It's an powdered enzyme that binds proteins together. I believe it's sold under the ActiveRM brand in the US.
I use it for attaching skin to chicken roulade etc. (e.g. https://www.chefsteps.com/activities/chicken-roulade)