hi,

first  of all I want to explain about the both of the ugc net and csir net exam and their purpose/

CSIR net: CSIR UGC NET is a national-level exam conducted by National Testing Agency (NTA) to select candidates for theposition of Junior Research Fellowship (JRF) and for determining their eligibility to appoint  as lecturers in Indian universities and colleges.

CSIR-UGC NET Exam for Science stream is conducted by CSIR in the following areas: -

1. Chemical Sciences

2. Earth Sciences

3. Life Sciences

4. Mathematical Sciences

5. Physical Science

you may chose any of the subject which is nearest to your education qualification. since you are from zoology background life science is the fair choice.

UGC NET:  On behalf of University Grants Commission (UGC), the National Eligibility Test (NET) is conducted for determining the eligibility Of candidates to become  Assistant Professor only or Junior Research Fellowship & Assistant Professor Both, in Indian Universities and Colleges.

however if you look for ugc net subjects there is no subjects which is vary much related with zoology back ground. however you may appear in both of the exams and either of the exam. however first analysis the syllabus, questions pattern and then take decision for exam preparation. follow the below link to know about ugc net subjects and syllabus:

https://www.ugcnetonline.in/syllabus-new.php