2 Behaviour

The behavioural characteristics of the morphotypes described above are of essential impor tance in the management of freshwater prawn grow-out facilities. BC males are aggressive, dominant and ‘territorial’, OC males are aggressive, subdominant and ‘non-territorial’, and SM males are submissive and ‘non-territorial’.

FIGHTING (AGONISTIC) BEHAVIOUR

The fighting behaviour of the three male morphotypes differs as males follow the develop mental pathway from SM through OC to BC. There is less physical contact and fewer dis plays of claw position and movement occur in SM than in OC and BC. As claw size increas es there is an increased risk of severe injuries caused by claws during interactions amongst OC and BC prawns. Male prawns have a hierarchical relationship. BC males are dominant over OC males which, in turn, are dominant over SM. Interactions between BC males are often only for show, with little physical contact. Those between BC and OC males involve more physical contact but BC males generally use threat displays and mere approaches in their relationships with SM. BC and OC males with equal claw size are evenly matched but a BC with larger claws than an OC, even if the OC is much larger, has an advantage. The dominance of BC over OC seems to confer priority of access to preferred areas (e.g. shaded protected crevices) but true territoriality (defending a fixed exclusive area to keep intruders out) has not yet been adequately demonstrated.

 

 

However, laboratory studies have shown that competitors are evicted from the vicinity of a limiting resource, such as shelter, food, and receptive females.

MATING BEHAVIOUR

Females approach males 2 to 3 days before their pre-mating moult. At first the female is chased away but later, after several hours of persistence, is allowed to remain near the male. About a day before the pre-mating moult the female is already totally accepted by the male, positioned below it or between its long second pair of claws. As a result of this early pair bonding, fertilisation can occur from several minutes to half an hour after moulting. It has been reported to occur up to nearly 22 hours later than the moult but this has been because researchers were pairing the males and females themselves, rather than allowing the nat ural bonding described above to occur. All three male morphotypes have similarly high rates of fertilising receptive females. Despite the fact that the spermatophores of SM are about half the size of those of BC males, the number of viable embryos following mating is depend ent only on the female size, not on the type of male morphotype.
Males do not attack or injure the females that they have just fertilized. BC tend to guard the female for two or three days following mating, by which time the female’s exoskeleton is hard enough to withstand attacks by other prawns. However, OC do not appear to groom or protect the females. There are reports of injuries inflicted by OC on females during this period (especially when more than one OC is present) but the infor mation is, at present, conflicting. Small males have been observed to mate with females by sneaking between a receptive female and her guarding BC male. A single SM has little or no chance to gain access to a receptive female guarded by a BC male. However, SM mating can be achieved when there are three or more SM present; while the BC is chasing away some of the runts, the female remains unprotected. Occasionally, following their pre-mat ing moult, females have been observed with several spermatophores attached to their sperm receptacle. There is some evidence that females are more attracted (through chemoreception) to BC and are more aggressive towards other male morphotypes. However, unfertilized females quickly lose all their eggs, which may be the reason why females that have undergone the pre-mate moult cooperate during mating with any of the male morphotypes.