MORPHOMETRIC STUDY OF EMBRYO DEVELOPMENT OF MACROBRACHIUM BORELLII (ARTHROPODA: CRUSTACEA)

LAVARIAS, SABRINA MARIA LUISA; H. HERAS; S. DEMICHELIS; E. PORTIANSKY; R.J POLLERO

INVERT. REPROD. DEVELOP.

INT SCIENCE SERVICES/BALABAN PUBLISHERS

Lugar: Balaban, Philadelphia; Año: 2002 vol. 41 p. 157 - 163

0792-4259

Embryo morphometry and developing time from just-laid eggs until hatching was described in the palaemonid prawn Macrobrachium borellii using a rapid non-invasive staging method. Embryos were kept in the laboratory under controlled conditions and development divided into 7 stages according to major morphological characteristics. This lecithotrophic, freshwater shrimp has a highly abbreviated type of development hatching after 39 ±2 days as postlarvae at 24 C. Morphometry was recorded using a stereoscopic microscope with an image analyzer. Area, perimeter, maximum and minimum diameters and shape were measured in yolk sac, egg-coat and eye, respectively and were statistically selected as the best to define the stages. Eggs are ovoid with a maximum diameter that varies from the moment of oviposition to the time of hatching from 1.5 to 2.0 mm, respectively. Water content and egg size increase along development, whereas egg shape only varies just before hatching when the egg becomes strongly ovoid. Egg coat and eye variables significantly increase as the embryo develops while all yolk variables decrease as the embryo consumes the vitellus. Yolk represents more than 95% of the egg at the time of oviposition falling to 22% by the time of hatching. The major yolk area decrease is observed between stages 4 and 5 which is coincident with a marked increase in catabolism. Using only egg coat, yolk and eye shape and maximum diameter, a researcher can straightforwardly identify a developing stage with an accuracy ranging from 70 to 100 %. This tool may be employed in other species provided they have transparent chorion.