Larval Growth Patterns in the Aesop Shrimp Pandalus Montagui

Larvae of the Aesop shrimp Pandalus montagui Leach (Decapoda: Caridea: Pandalidae), were reared in the laboratory at 5 different temperatures (6, 9, 12, 15, and 18°C), and their growth patterns were analyzed in terms of molting frequency, size increments (total length, TL, carapace length, CL), and increase in larval dry weight (W). Pandalus montagui passed through 6 zoeal and 2-5 decapodid stages. While 2 of the latter occurred consistently (obligatory stages), up to 3 additional (facultative) decapodid stages were passed before metamorphosis to the first juvenile. Molting occurred at regular intervals, with little interstage variation, so that the instar number could be described as a linear function of the time of development, with an increasing molting frequency at increasing temperatures. A nonlinear relationship (power function) was found between average intermolt duration and temperature; this regression was linked with data for water temperatures measured during the spring near Helgoland (southern North Sea), in order to predict the approximate duration of larval development and peak settlement in the field. From instar I-VIII, larval size increased as a linear function of the number of molting cycles, but no significant growth and no further morphological changes were observed in later (facultative) larval stages. The morphometric relationship between TL and CL remained linear throughout larval development, with an increasing trend in the TL:CL quotient. W increased exponentially with the number of instars, and as a power function of larval size. The overall patterns of larval development and growth in P. montagui are compared with those known from other pandalid species and in other caridean shrimps.