Towards the end of the dive I was hanging out under the boat and started watching a Sergent major fish. They are common throughout the Caribbean and I have seen hundreds (maybe thousands) of them over the years. But it’s still interesting to observe their behavior, especially when it comes to their nesting.
Wikipedia says, “The sergeant majors is an oviparous species in which the males create nests where the females to lay their egg masses on rocks, reef outcrops, shipwrecks, and pilings.[5] The males actively chase the females in courtship before the female releases approximately 200,000 ref, ovoid eggs which are attached to the substrate by a filament”
Reefnews.com does a good job explaining what happens next,
After building this nest, the male Sergeant Major will stay near the nest for several days to guard the eggs until they hatch. The female will leave during this time. The male will chase away all other fishes to keep the eggs from being eaten. The male Sergeant Major can be very aggressive during this time, and will even attack people in the water if they accidentally get too close to the nest. Although the Sergeant Major probably couldn’t hurt anyone, it will fearlessly try to drive away anybody that it thinks is too close to its nest.
http://www.reefnews.com/reefnews/photos/sgtmjr02.html
The Digital Gallery Blog 