Maturity stages of shrimp (Pandalus borealis Krøyer 1838. Method for classification and description of characteristics

Sammendrag

Pandalus borealis is a protandric hermaphrodite that shows a great variation in both age at sex change and in the proportion of males that become females. This plasticity is believed to be a phenotypic response to maximize individual reproductive success. Since 1992, we have classified all shrimp taken for length measurements into maturity stages in order to understand more of the population structure of shrimp in the Barents Sea and Svalbard area . The development of sex characters and transition from male to female shrimp was characterized by seven stages using the morphology of the endopod of the first pleopod, sternal spines and head roe. After the juvenile stage, shrimp mature first as males (Stage 2). Thereafter they become intersex or transitionals (Stage 3) before they develop into females with head roe (Stage 4). When the females mate, the roe is spawned under the abdomen and kept there by the pleopods (Stage 5), where it stays until the larvae hatch (Stage 6). Some females then enter a resting period (Stage 7), while others start on a new cycle with head roe (Stage 8).