Breeding crayfish: From mating to hatching
The mating of the Astacidae using Astacus astacusas an example
When water temperatures drop in autumn, mating takes place. During this process, the females are held by the males with their claws and turned onto their backs or lateral position. Females are cooperative when ready to mate, so even much smaller males are able to mate with physically superior females. During this mating, the males attach small white rod-shaped spermatophores, about one millimeter thick, to the female with their gonopods. These are usually found ventrally between the last walking legs or on the tail fan.
Reproduction of the North American Cambaridae using Procambarusas an example
Immediately before mating, contact occurs between the partners by touching or by certain movements with the claws. Sometimes mating attempts between males can be observed, which might be due to the fact that one of the animals has regenerated and therefore small, rather whiny shaped claws. Experiments with Procambarus clarkii show that in this species contact is also made in a chemical way.
Especially the aggressiveness of some males and the relative passivity of the females is a critical factor in the first encounter between the animals. It could be observed that "violent" males are rejected by the females.
The further course of contact serves to ensure that passive animals are sexually stimulated and the aggressive behavior of potential mates is reduced. Only in this way is mating made possible. At the beginning of mating, the male grasps the female partner with his claws and tries to turn her onto her back or side. With its walking legs it clasps the body of the female and tries to hold her in this way. Helpful in this process are the ischium hooks at the base of the male's legs, which serve as clasping organs. If the attempt is successful, the ventral sides of the partners face each other and mating can begin. During this process, sperm is directed from the vas deferens into one of the first two gonopods and is carried on by the second gonopod, which acts as a piston. The first gonopod penetrates the annulus ventralis. A small body opening on the underside of the female. Pressure from the second gonopod deposits sperm in this permatotheca.
Mating lasts approximately 15 minutes, after which the female is released. Shortly after mating, usually after a few hours, the female cleans the setal fringes on the swimming legs of the abdomen with her hind walking legs and then begins to lay eggs. In other genera, the female may also store the sperm for a long time and only at a later time does oviposition occur. In Orconectes females it can take up to eight months before egg laying occurs.
During oviposition, the abdomen is pushed forward to the posterior margin of the cephalothorax, forming a kind of brood chamber. Mucus from the albumen glands is released into this spar chamber. This mucus forms an elastic skin as soon as it comes into contact with water. The female lies down on her side or back and the eggs emerge from the gonopores into this mucus tent. Now the sperm is released from the annulus ventralis and fertilization of the eggs takes place. Through constant beating of the webbed legs and the eggs' own weight, each egg is firmly attached to the pleopods by a stalk or thread, the funiculus, while the mucus hardens. Eggs that are not fertilized or have not been attached to a funiculus are usually eaten by the female. The female then turns back to normal position.
The attached eggs on the abdomen of the mother are carefully cared for by her. This is done on the one hand by rhythmic movements of the webbed feet, so that the eggs are constantly washed around and oxygen and metabolic by-products are washed away. On the other hand, they are also cleaned of impurities mechanically with their walking legs. During this time the females hardly leave their hiding place and eat very little or nothing.
The hatching process
At hatching, the egg capsule ruptures, but remains attached to the female by the filament. At this stage, the Cambaridae are not as developed as the Astacidae; the latter usually hatch one larval stage earlier. The hatchling is further connected to the mother by the telson filament (a phylogenetic feature of crayfishes) at the inner egg membrane. If the hatchling is accidentally torn loose, it clings to the existing structures of the maternal abdomen with the specially shaped hooks of its claws.
Three larval stages occur: in the first stage, hatchlings have no uropod and the carapace is enlarged by the yolk sac. When this is depleted, the molt to the second stage approaches. After this molt, the hatchlings still remain attached to the abdomen. Additionally, pheromones cause the juvenile crabs to remain attached to the mother. After molting to the third stage, the uropods appear and the juveniles begin to move increasingly freely.
Since crayfish are cannibalistic, it happens that some are consumed by conspecifics, even by siblings. Especially in the aquarium keeping it comes dadruch during the first time, when animals frequently shed their skin, to large losses.
The mating of Parastacidae using the example of Cherax destructor
A few days before mating, the female is already busy preparing and cleans the pleopods and the underside between the walking legs with the last two pairs of walking legs. One day before mating, the male is also in a mating mood, still behaving aggressively towards the female and chasing her. Eight hours before mating, the aggressive behavior decreases and the male begins to tenderly touch and caress the female with his antennae. Just before mating, both mates exhibit this tender antennal ritual, with the female then lying on her back and the male climbing on top of the female.
The female then rolls up her abdomen and the male covers it with his abdomen. The male deposits the sperm (small white droplets called spermatophores), on the underside of the female's abdomen or between the last pair of walking legs. They then separate and the male moves away. The female remains on her back for a few more minutes, secreting a gelatinous substance that flows into the cavity formed by the impacted abdomen and covers the pleopods (the mucus tent). The bluish eggs are then ejected and directed into this gel pack. The female turns back to normal position with her tail folded and seeks a hiding place. After about 18 hours, the mucus tent is dissolved and the eggs are attached to the hairs of the pleopods.
However, other behaviors have been observed in parastacid mating, with the female taking a dominant role in the mating ritual. This involves the female attempting to place the male on his back in order to mount him. There can also be great differences in the duration of mating, which sometimes takes no more than a minute. Mating usually takes place in the late afternoon or at night. The timing of egg release also varies greatly and does not have to occur immediately after mating. The female may wait hours, days, or weeks before beginning to spawn.
Source: Freshwater crayfish from around the world - Chris Lukhaup/ Reinhard Pekny
