( Fins ( ( are ( ( used ( by fish ) ) ( ( ( ( to ( move ( through ( the water ) ) ) ) ( but also ) ) ( to ( ( ( ( ( steer , ) stop ) and ) maintain ) ( ( ( their position ) , ) ( ( the latter ) ( in conjunction ) ) ) ) ) ) ( with ( the ( swim bladder ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Fins)) (VP (VBP are) (VP (VBN used) (PP (IN by) (NP (NN fish))) (S (VP (VP (TO to) (VP (VB move) (PP (IN through) (NP (DT the) (NN water))))) (CONJP (CC but) (RB also)) (VP (TO to) (VP (VB steer) (, ,) (VB stop) (CC and) (VB maintain) (NP (NP (PRP$ their) (NN position)) (, ,) (NP (NP (DT the) (NN latter)) (PP (IN in) (NP (NN conjunction))))))) (PP (IN with) (NP (DT the) (JJ swim) (NN bladder))))))) (. .)))
Fins are used by fish to move through the water but also to  steer, stop and maintain their position, the latter in conjunction with  the swim bladder.
(ROOT (S (NP (NN Fish)) (VP (VBP use) (NP (NP (DT some)) (PP (IN of) (NP (PRP$ their) (NNS fins) (S (VP (TO to) (VP (VB propel) (NP (PRP themselves)) (PP (IN through) (NP (NP (DT the) (NN water)) (CC and) (NP (NP (DT some)) (PP (IN of) (NP (PRP$ their) (NNS fins) (S (VP (TO to) (VP (VB steer)))))))))))))))) (. .)))