Low velocity vascular channels seen along left testis(caliber3-4 mm)suggestive of left sided varicocele came in my ultrasonography, is surgery required?

No: Pain ; discomfort in left testicle will likely settle down. Varicoceles needing surgery are large enough to feel like a "bag of worms" when ur standing erect, or there is persistent discomfort over long period of time, left testicle >15% small than right or sperm count shows high % non motile forms. If pain was severe ; sudden must consider intermittent testis torsion ; will come ; go ; us -ve.

Not just: For that alone. If ultrasound performed for some other reason then perhaps, but i cannot address that without knowing.

Varicocele: Varicoceles do not require surgery, they are usually asymptomatic. Unless you have an infertility problem, i would leave it alone.