Feeding geckos should be fine, but if they are collected in your house or neighborhood I'd be 100% sure that no pesticides are being used. I wouldn't want you to poisen you fish with lizards that have ingested pesticides or insects that have been exposed to them.
To catch geckos or other little fast lizards sqratch, I would suggest trying a small noose. This sounds farfetched but, believe it or not, it works wonders. I have used small nooses to catch anoles tons of times. Just get a long, slender stick and some dental floss or fishing line and make one up. Small lizards freak out when a hand comes at them, but for some reason they stay still for inanimate objects, even if it is a noose that is about to lasso them around the neck.
To catch geckos or other little fast lizards sqratch, I would suggest trying a small noose. This sounds farfetched but, believe it or not, it works wonders. I have used small nooses to catch anoles tons of times. Just get a long, slender stick and some dental floss or fishing line and make one up. Small lizards freak out when a hand comes at them, but for some reason they stay still for inanimate objects, even if it is a noose that is about to lasso them around the neck.