Bone won't connect to specific mesh

So i was try to animate a whale with armature, and i tried my best to connect the bones with the mesh. But when i goes to pose mode,the tail-part of the armature won’t move the tail, instead its posing the another part of the object. I was going to weight paint and make the weight same as the another part. What should i do? please help cause it was my college assignment

your left tail bone isn’t parented to your bone.007. in edit mode select the left tail bone, then shift click bone.007 the left tail should be displayed in orange and the bone.007 should be displayed in yellow.
then CTRL+P and choose connected or keep offset, in your case it should be connected.
then, re-assign the automatic weight by selecting your mesh, then your armature. and with CTRL+P, choose with automatic weight. afterwards you can refine the weights with weightpaint.