It is a dish of relative popularity amongst Malaysians and Singaporeans and tourists there, although it is generally not categorised as cheap hawker fare. 

A typical fish head curry served in a claypot costs between $10-20 and some of the best can be found in hawker centres and neighbourhood food stalls.

The origins of the modern dish began in Singapore, with a chef wanting his South Indian-style food to cater to a wider clientele, notably Chinese customers who considered fish head a special delicacy. Today, restaurants of not only Indian, but Malay, Chinese and Peranakan associations serve variations of this dish.

Tamarind (asam) juice is frequently added to the gravy to give it a sweet-sour taste (see asam fish); this variety of fish head curry normally has a thinner, orange gravy. Additionally, a certain amount of coconut milk is often used in the curry.

According to wikipedia.