Start the work by drawing two ovals & line as shown.
Draw outline for fins, mouth & tail. Also draw a line in the middle of the body and a circle.
Make head & eye.
Draw outline for body.
Make tail & fins.
Draw retinas, mouth & gill as shown.
Make lines over the tail and fins as shown.
Make diagonal lines going from left to right as shown.
Draw diagonal lines going from right to left as shown.
Finally, make necessary improvements to finish.