A histological evaluation of development and axis formation in freshwater fish ectoparasite Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura)

Abstract

The present investigation was carried out to underscore the developmental events of a crustacean ectoparasite of fish, Argulus bengalensis. Serial histological sections of the embryo were made at lateral, sagittal and longitudinal planes to explain its cleavage, gastrulation and axis specification. The centrolecithal egg of A. bengalensis underwent meroblastic superficial cleavage. The cleavage initiated at the future dorsal side of the egg within 5 h to 5 h and 30 min of incubation. Consequently, a small mass of energids appeared superficially at the future dorsal side within 6 h. Later, energids were found at the future ventral and lateral sides. A syncytial blastoderm was formed around the centrally placed yolk material which was transformed into a cellular blastoderm within 30 h of incubation. In the blastoderm, two cell masses were formed at the dorsal and ventral part which initially extended towards each other and later spread out though future anterior-posterior direction. The pressure exerted by the cell flow displaced the entire yolk material at the future postero-ventral side. At the time of egg laying, a prototype of the embryonic axes is determined. The substratum side of the egg formed the dorsal part, whilst the side facing water turned to the ventral part. The broader end of the egg formed the anterior side and the narrow end formed the posterior side of the embryo. The anterior-posterior axis formation was initiated within 72 to 96 h of incubation when the blastodermal cells displaced the yolk material at the future posterior end. Within 120 h of incubation, the germ layers of the embryo were determined. The study reveals that the cleavage pattern of A. bengalensis shows close similarities with that of the Malacostraca amongst the crustaceans and dipteran and hymenopteran amongst the insects.

Mutualistic association of rotifer Philodina roseola with the branchiuran fish ectoparasite Argulus bengalensis at its embryonic stage

“…The appearance of P. roseola on the egg strips, under both laboratory and field conditions, proves that this rotifer population is a natural inhabitant of the farm water; the same fact was also noted by Fayer et al [7]. At the time of laying, each egg clutch is covered with a secretion from the paired collateral glands [8], which subsequently solidifies into a jelly coat [9]. According to Davis [10], the larvae hatch by creating a furrow through the egg envelopes using their dorsal organs as well as by increasing the osmotic swelling of the inner egg membrane.…”

Histological and ultrastructural investigation of the female reproductive system of Argulus bengalensisRamakrishna, 1951 (Crustacea: Branchiura)

“…The egg laying process of the species recorded in a prior study (Banerjee et al, 2015a) revealed that median oviduct serves as a transit passage for the eggs but does not retain the eggs inside. As the collateral accessory glands open into this passage, it is hypothesized, that while passing through it, the eggs are embedded in the glandular secretion.…”

“…Rapid proliferation of the glandular cells is evident from the dynamic states of the nuclei which add further proof regarding the holocrine nature of the gland. The secretion of this gland presumably contributes to the jelly coat which subsequently solidifies (Banerjee et al, ) to form the outer egg envelop enabling the egg clutch to adhere onto the substratum.…”

“…Although the accessory reproductive glands of the female Argulus sp. have not been reported in the earlier literature, the existence of such glands could be apprehended from observing the outer envelops of the egg where a jelly coat is clearly visible outside (Banerjee et al, ). In the present study also, attention has been focused on identifying and locating the accessory reproductive glands.…”

“…In insect pests, the accessory gland is highly specialized and its function is important in their reproductive process (Adiyodi and Adiyodi, 1975;Lococo and Huebner, 1980;Takaoka et al, 1989;Kaulenas, 1992). Concerning other aspects of their reproductive biology, a detailed study of egg laying, development, hatching and the temperature-dependent life cycle was done earlier by Shafir and van As (1986) in Argulus japonicus, and recently by Banerjee and Saha (2013) and Banerjee et al (2014aBanerjee et al ( , 2015a in Argulus bengalensis. Many researchers, even prior, had conducted studies on the reproduction and population dynamics of Argulus spp.…”