The Thumbprint Emperor (Lethrinus harak) is also known as the Blackspot emperor . They are fairly common inhabitants of rubble areas and reef sides in Tanzania.
Thumbprint Emperor have a typical emperor body shape with a slightly humped back and a long sharpish face and jaw. In good light the body is a silver color with a characteristic short black line ringed in yellow in the mid dorsal area just below the lateral line. Some specimens have short light blue lines or dots on the face. The fins are translucent with a pinkish tint. The largest specimens we have seen have been around 35 cm. They do however grow up to 50 cm.
THUMBPRINT EMPEROR IN THE WILD
The Thumbprint Emperor is generally always seen solitary on the edges of reefs and in sandy rubble areas. The juveniles seem to prefer grassy beds and are usually seen singularly in grassy beds. Research has indicated that they are territorial and that the territories overlap each other slightly.
Thumbprint Emperor are widely distributed across the tropical Indo-Pacific, from East Africa up to the Red Sea and across to the Solomon Islands and down to North Eastern Australia. We have seen them on reef tops and on rubble areas down to depths of approximately 22 meters although they are found deeper.
Thumbprint Emperor have a varied diet, feeding on mainly on crustaceans but they will take small fish. Their diets vary with maturity and locally available prey items. Adults are said to prefer primarily a crustacean diet. They have been recorded entering freshwater estuaries to feed.
In Kenyan waters they spawn from October to April and it is assumed that they do the same in Tanzanian waters. Usually they are territorial, but they congregate in spesific areas for group spawning on certain tides and moon phases. The eggs are released into the water table. The eggs which are round and transparent float and hatch after 18 hours.
The study in Kenya found that females were sexually mature at 19.6 cm and males at 18.7 cm, equating to ages of 2.6 years for females and 2.4 years for males.
Thumbprint Emperor are heavily exploited commercially in most areas particularly in the South Sea Islands. In Fiji size limitations have been set to try and allow the populations to recover. In Tanzania they are caught by fishermen in traps and on lines and are occasionally netted in the shallows. They are usually sold fresh. Many local fishermen are aware of their spawning times and locations and gill net them. This has a destructive effect on population levels.
THUMBPRINT EMPEROR CLASSIFICATION
Species: L. harak
Improved Growth Estimates for Lethrinus harak:
Measuring Increments, Adjusting Ages, and Fitting
Flexible Growth Models