P. Collins, A. Petriella
Abstract:
The crustacean body is confined within a hard exoskeleton, so the growth is discontinued and characterized by an explosive expansion after the ecdysis. The immediate increase in size is due to an addition in the volume of body fluids, and subsequently there are enlargements of muscles, glands and other tissues. As a consequence of the discontinuous nature of growth it can be broken down in two components: the moult increment and intermoult period. The moult period, or its frequency, may change depending on the food quality, temperature, disease and other factors which may affect neurohormonal functions and its ecdysis cycle.
Macrobrachium borellii (Nobili), is an endemic prawn with a complete abbreviated larval development in freshwater environment of South America. It inhabits the floodplains of Argentina, Uruguay, southern Brazil and Paraguay.
Juveniles and adults of M. borellii (95) were kept individually in glass containers (3.5 l). In intermoult stages, three days after the moult, cephalothorax length (Cl) was measured. The relationship between Cl premoult and Cl postmoult were analyzed.
An isometric increase of Cl was observed in juveniles (slope: 1.01) and a negative allometric for females and males (slope: 0.85 and 0.87 respectively). Intermoult period varied proportionally direct with the increase in prawn size, being linear in juveniles and positively exponential in females and males. The size increase was larger in males than in females but there was not a significant difference. The relationship between growth rate and intermoult period was negatively exponential in juveniles, females and males. The growth rate decreased with the increase in the intermoult period. The growth rate decreased with the size, in a negative exponential form too. Females and males values did not statistically vary but juveniles and adults values were statistically different.
The juvenile phase is finished by a change in the growth level and maybe with the gonadal maturation. The difference in the allometric level of male-female was relatively small and in some cases of uncertain significance.
(Zoologisches Institut (Biologiezentrum) Universitat zu Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany)