Abstract

The juveniles of red-legged banana prawns Penaeus indicus and white banana prawns P. merguiensis are difficult to distinguish. Gel electrophoresis, with the enzyme malate dehydrogenase, clearly separated into species both large and small prawns. Four morphological characters were measured from juvenile prawns (identified using electrophoresis): three of these provided reliable separation into species. The mean ratio of the distance from the anterior-most dorsal rostral tooth (first tooth) to the tip of the rostrum (L ₁ ): to the distance between this tooth and the second tooth (L _1,2 ) was higher for P. indicus (3.16) than P. merguiensis (1.56). All juvenile P. indicus had the first tooth posterior to the antennular peduncle, while it was anterior for all P. merguiensis. More than 90% of P. indicus had six rostral teeth behind the eye, while over 90% of P. merguiensis had five teeth behind the eye. Damage to the rostrum prevented measurements of the position of the first tooth in 20 to 30% of juvenile prawns. Combining the measurements of the ratio of L ₁ : L 1,2 and the count of the number of rostral teeth behind the eye meant that all prawns could be unambiguously identified.