Driving to the Langkawi Fish Market takes about 17 minutes from the port. Head northwest on Persiaran Putera toward Lencongan Putra. Turn left at Persiaran Mutiara, then make a sharp right turn to merge onto Jalan Padang Matsirat. After that, turn right at Jalan Padang Gaong. Finally, turn left at Jalan Ulu Melaka, and you will see the fish market right there. If you drive there, avoid driving at night because there are some rural roads on the way that have inadequate lighting and livestock might wonder alone at night.
For more info, see Langkawi Port Guide