Fish Farming Business (mackerel)

Hi People
I would like to know why fish farmers in nigeria have not gone into breeding Mackerel. I mention Mackerel because this is without doubt one of or the most popular fish eaten in Nigeria. Yet virtually all Mackerel consumed is being imported from abroad. I am aware that fish farmers are rearing predominantly catfish and tilapia, yet no one seems to focus on Mackerel.

Can anyone enlighten me on why this is so or have I just discovered a massive gap in the market for home grown Mackerel.

Cheers
Ese