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Gill arch morphology of the Cape hakes Merluccius capensis Cast. and M. paradoxus Franca
Bentz, K.L.M. (1976). Gill arch morphology of the Cape hakes Merluccius capensis Cast. and M. paradoxus Franca. Fisheries Bulletin (South Africa) 8: 17-22
In: Fisheries Bulletin : Contributions to Oceanography and Fisheries Biology = Visserye-bulletin : bydraes tot oseanografie en visserybiologie. Department of Agriculture and Fisheries. Sea Fisheries Institute: Cape Town, more

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Keywords
    Body size; Diets; Feeding behaviour; Life cycle; Organism morphology; Respiratory organs; Amphipoda [WoRMS]; Euphausiidae Dana, 1852 [WoRMS]; Merluccius Rafinesque, 1810 [WoRMS]; Merluccius capensis Castelnau, 1861 [WoRMS]; Merluccius paradoxus Franca, 1960 [WoRMS]; Myctophidae Gill, 1893 [WoRMS]; Marine

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  • Bentz, K.L.M.

Abstract
    At {approx} 40 cm total fish length, the diet of M. capensis changes from amphipods, euphausiids and a low percentage of myctophids to a virtually exclusively piscivorous diet of predominantly small hake. In M. paradoxus the change from a zooplanktivorous to a piscivorous diet occurs at a fish length of {approx} 50 cm. A M. capensis of 43 cm length and a M. paradoxus of 49 cm have the same raker length (9 mm). A M. capensis of 43 cm length and a M. paradoxus of 50 cm have a similar gap between rakers (2.7 mm). Hence, it appears that when the raker length reaches +- 9 mm and the gap between gill rakers reaches +- 2.7mm the gills become inefficient for zooplankton filtering and a change in feeding habit takes place. It is clear that feeding habits and gill structures are closely related and that for M. capensis and M. paradoxus the efficiency of the filtering apparatus does not increase with fish size. The gill rakers develop no further processes and, owing to an increase in the gap between rakers, the mesh size of the filtering area becomes more coarse and therefore less efficient. This sets a limit on the ability to retain smaller prey so that larger prey is taken as the individuals grow.

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