MEPS 145:43-51 (1996)  -  doi:10.3354/meps145043

Field observations of moult cycle, feeding behaviour, and diet of small juvenile tiger prawns Penaeus semisulcatus in the Embley River, Australia

Heales DS, Vance DJ, Loneragan NR

Juvenile tiger prawns Penaeus semisulcatus (2.5 to 5.5 mm carapace length) were collected on an intertidal seagrass bed in the Embley River estuary in the Gulf of Carpentaria, Australia. Prawns were sampled every 2 h over one 24 h period in the pre-wet (early October) and over one 24 h period in the late-wet season (late March) and the moult cycles and foregut contents determined. Premoult prawns were found mostly between 12:00 and 22:00 h and ecdysis occurred mostly between 20:00 and 0:00 h. A mean moult period of 3.0 d was estimated from the percentage of the prawns in premoult and ecdysis stages in early evening samples. On a scale of 0 (empty) to 10 (full), the mean foregut fullness of small juveniles was greater than 4.5 during both the day and night in each season. Copepods, filamentous algae, diatoms and unidentified material were the most common prey in both seasons. Insect larvae were more common in the pre-wet and nematodes and ostracods were more common in the late-wet. Little diel variation in diet was noted. Rapid foregut passage rates under field starvation conditions showed that between 55 and 60% of foregut contents was cleared in 1 h. This result, and the values for mean foregut fullness over 24 h, suggested that small prawns fed continuously through the day and night. Further field experiments in the presence of food showed that both hard and soft prey items were cleared from the foregut within 2 h and also that moult stage affected the feeding behaviour of prawns. Intermoult prawns maintained means of foregut fullness greater than 7, while premoult prawns ate less.

Penaeid · Juvenile · Moult cycle · Moult period · Feeding behaviour · Diet

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