Dynamics of Stock and the Existing Harvest Control Rule of NEA Cod

Abstract

The setae of the mouthparts of juveniles and adults of the giant freshwater prawn Macrobrachium rosenbergii and the australian red claw crayfish Cherax quadricarinatus was examined. Prawn M. rosenbergii and crayfish C. quadricarinatus are important objects of world freshwater aquaculture. Main types of setae and its distribution on the mouthparts were determined. The interpretation of setae with relation to intensity and direction of mechanical impacts is given. The structures on the setae surface vary in dependence of mechanical load intensity. The following sequence of structures types as long thin setulas, short setulas, denticles, the absence of external elements combined with thick shorten setaes, have direct correlation with intensity of the mechanical impact. The presence of denticles and ordering short setulas indicates that only one side of setae is under the mechanical action. The fact of impact of significant body size transformation during ontogenesis on the setae distribution on the mouthparts was established. The tendency of length reduction and/or disappearance of setulas and denticles was observed. Lenth of setae decreases against the body size. The increase of number of setae takes place and tight grouping of main types of setae occurs. An assumption made that with increase of body size the efficiency of separate setulas decreases and, for adult individual, groups of setae should be considered as functional units.