In this study, the interrelationships between various morphometric characters, viz., carapace width and length and chelar propodus length and height in males, as well as carapace width and length and abdominal width and length in females, were estimated using a total of 980 crabs, Portunus pelagicus. The carapace width/length -weight relationship was studied in both sexes on a total of 1188 crabs using the allometric growth equation of Von Bertalanffy. The allometric relationships between the characters of this set suggest that most relationships are positive and highly significant. The 'b' values for carapace width-weight in males and females were 3.607 and 3.293, respectively, and for carapace length-weight they were 3.049 and 2.774, respectively. The results show a significant deviation from an isometric growth pattern. An analysis of covariance indicates that there is a significant difference between sexes with respect to the carapace widthweight relationship. RÉSUMÉDans cette étude, les interrelations entre divers caractères morphométriques, viz., largeur et longueur de la carapace et longueur et hauteur du propodite de la pince chez les mâles, ainsi que la largeur et longueur de la carapace et largeur et longueur de l'abdomen chez les femelles, ont été estimés en mesurant un total de 980 crabes Portunus pelagicus. La relation taille de la carapace (largeur/longueur) versus poids a été étudiée dans les deux sexes sur un total de 1188 crabes en utilisant la courbe de croissance de Von Bertalanffy. Les relations allométriques entre ces caractères suggèrent que la plupart des interrelations sont positives et hautement significatives. Les valeurs de « b » pour la relation largeur de la carapace/poids chez les mâles et les femelles sont respectivement de 3,607 and 3,293, et pour la relation longueur de la carapace/poids de 3,049 et 2,774, respectivement. Les résultats montrent une déviation significative du modèle de croissance isométrique. Une analyse de covariance montre qu'il existe une différence significative entre les sexes au niveau de la relation largeur de la carapace/poids. 1 )
Food habits of the blue swimmer crab, Portunus pelagicus were investigated using specimens collected from trawl catches in the Mandapam region, Tamil Nadu, along the east coast of India (9 • 20-25 N 79 • 5-10 E), during the period January to December, 1999. The stomach contents of 452 crabs, ranging from 61 to 180 mm carapace width, were analysed. Their diet included crustaceans, molluscs, fishes, unidentifiable matter, and debris. In adult crabs, crustaceans constituted the dominant food source and these were present in 78.43% of the stomachs analysed. The stomach contents of juveniles and sub-adults were dominated by debris. There was no significant difference between sexes in the frequency of occurrence of food items or in their "percentage points" [= the (virtual) percentual contribution to the fullness of a 100% full stomach]. However, there was a difference between the stomachs of ovigerous and non-ovigerous females. There were also significant differences in the preference for food items in the different size groups of the crab. The results collected from the present study showed that P. pelagicus exhibits, in this region at least, a clear preference for crustaceans. RÉSUMÉLes habitudes alimentaires du crabe « étrille bleue », Portunus pelagicus ont été étudiées en utilisant des specimens collectés par prises an chalut dans la région de Mandapam, Tamil Nadu, le long de la côte orientale de l'Inde (9 • 20-25 N 79 • 5-10 E), au cours de la période janvier à décembre 1999. Les contenus stomacaux de 452 crabs, de 61 à 180 mm de largeur de carapace, ont été analysés. Leur régime incluait des crustacés, des mollusques, des poissons, de la matière non identifiable et des débris. Chez les crabes adultes, les crustacés constituaient la source alimentaire dominante et ceux-ci étaient présents dans 78,43% des estomacs analysés. Il n'y avait pas de différence significative entre les sexes dans la fréquence de présence des différents aliments ou dans leurs « percentage points » [= la contribution en pourcentage (virtuelle) au remplissage d'un estomac plein à 100%]. Cependant, il y avait une différence entre les estomacs des femelles ovigères et non-ovigères. Il y avait aussi des différences significatives dans la préférence pour les différents aliments dans les différents groupes de taille du crabe. Les résultats obtenus dans cette étude ont montré que P. pelagicus montre, dans cette région au moins, une préférence évidente pour les crustacés.1 )
Larvae of Portunus pelagicus (Linnaeus, 1758) were reared in the laboratory on hatching from wild ovigerous females collected from Palk Bay, southeast India. The larval stages included four zoeal stages and one megalopa. The megalopa moulted to the first crab instar. The zoeae and megalopa were very similar to those of other portunids. The duration of each of the first two zoeal stages was 3-4 days, the following two stages 2-3 days, and the megalopa 3-5 days, reaching the first crab stage in 15-17 days. All zoeal and megalopal stages are described in detail and are documented with illustrations.
The growth of hatchery produced Portunus pelagicus crabs was monitored under laboratory conditions by recording growth at each moult from the 1 st crab instar onwards. Male and female crabs attained sexual maturity by their 12 th and 14 th moult, respectively. The experiment lasted for 455 days when the last crab died. This paper describes the growth of male and female crabs in each moulting stage, with details of their carapace width and length, chelar length and height, abdominal width and length, and total weight. Moulting frequency, secondary sexual characteristics, and moult increments were also monitored.
The present investigation provides information on the fecundity of the blue swimmer crab, Portunus pelagicus (Linnaeus, 1758), expressed as the number of eggs counted, and its relationship with carapace width (CW) and total body weight of the female crab, as well as with the weight of the egg mass (i.e., clutch size). Berried crabs were collected fortnightly from shrimp trawls taken in the waters off Mandapam (09°20-25'N 79°5-10'E) on the southeastern coast of India. A total of 42 ovigerous females with eggs in early development (initial stage: yellow/orange colour) were used for the analysis. The fecundity measured ranged between 60 000 and 1 976 398 in crabs with carapace widths of 100 to 190 mm. Statistical studies revealed that among the different relationships, carapace width and fecundity are better indices for the estimation of reproductive potential, than the body weight of the crab.
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