20-30 gm is not a small size for blood collection

for starting you need to practice on 20-30 fishes

once you get experience to holding fish in one hand and able to use syringe wit other hand

it will become easy

Yes of curse can collect blood samples from this weight from the ventail or the heart

Yes you can collect blood from the heart by syringe needle.

If u know how to take blood from caudal peduncle then u can easily draw blood from as small as 10g fish or sometimes from less than 10g fish. And if the fish is 20-30g then I recommend u not to draw blood from the heart. U can easily draw blood from the caudal peduncle end without killing the fish.

Dear researcher, u can collect blood from the caudal peduncle end without killing the fish ,it is easy method and good for the quantity of blood collected

Certainly, it is feasible to obtain blood from Nile Tilapia fish weighing approximately 20 to 30 grams. The usual approach involves utilizing a method known as "caudal puncture," wherein a small quantity of blood is gathered from the caudal vein situated near the tail. This technique is frequently employed for studying fish and assessing their health. Nevertheless, it's crucial to emphasize that only trained individuals should conduct this procedure, following ethical and humane principles for handling animals.

Yes, just before the caudal peduncle region.

you can collect the blood directly from the heart or caudal peduncle end