Abstract. The current study investigated the impact of methoprene during different phases of oogenesis in the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae), a non-target organism abundant in the wetlands of Wayanad, Kerala, India. Sublethal doses of methoprene impaired ovarian growth as evidenced by reduction in gonadosomatic values, fall in mean oocyte diameter and histopathological changes in all the phases of oogenesis. A significant drop in the proportion of mature oocytes in the experimental crabs were noticed, i.e. methoprene treatment delayed the growth of avitellogenic oocytes to previtellogenic and previtellogenic to early, middle or late vitellogenic stages. Reduction in proliferation of oogonia in the germinal zone and ruptured oolemma in chromatin nucleolus and perinuclear stage oocytes was persistent. Histopathological changes in the primary vitellogenic oocytes include karyoplasmic clumping, perinuclear space atresia, shrinkage and vacuolation of ooplasm, reduction in size of yolk globules and vacuolated globules and degeneration of follicle epithelium. Methoprene negatively affected yolk platelet formation as evidenced by the irregularly fused and distorted yolk platelets of late vitellogenic oocytes. The observed cellular deformities possibly suggest the direct effects of methoprene on the oocytes through general metabolism and growth or through hormones controlling ovarian growth.

The light and ultrastructural observations on haemocyte profile of the freshwater crab Travancoriana schirnerae demonstrated three cell types: agranulocyte, granulocyte I and granulocyte II. Agranulocytes are the smallest of the haemocyte types, comprised 38% of the haemocytes, devoid of granules and showed high nucleoprotoplasmic ratio. Their cytoplasm contained numerous free ribosomes, vesicles of smooth endoplasmic reticulum, few mitochondria with parallel cristae and vacuoles. Granulocytes I (37%) are the largest of the haemocyte types, characterized by the presence of numerous granules (26 to 61) of varying size, shape and densities and organelles like mitochondria, free ribosomes and peripheral vacuoles and displayed low nucleoprotoplasmic ratio. Granulocytes II (25%) contained large electron dense granules (10 to 23) and organelles like free ribosomes and vacuoles and showed intermediate nucleoprotoplasmic ratio. Unlike granulocytes, agranulocytes exhibited prominent pseudopodial projections suggesting a phagocytory function. This study revealed the unusual occurrence of a binucleate agranulocyte and a rare phenomenon called clasmatosis of granulocyte II, wherein part of the cell fragments off along with cytoplasmic contents devoid of nucleus.

The current study investigated the impact of eyestalk ablation on androgenic gland activity in the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae). Bilateral eyestalk ablation during active phase (March-June) induced hypertrophy and hyperplasia of the gland as evidenced by increased width of the gland, thickness of the connective tissue layer, increase in cell and nuclear diameter with predominance of type I cells. This hypertrophy and hyperplasia was not followed by secretory activity during active phase which possibly suggests the non-functional nature of hypertrophy and hyperplasia. Unilateral destalkation during active phase neither caused hypertrophy nor hyperplasia of the gland cells probably because these crabs may still receive the inhibitory principle from the remaining intact eyestalk causing the gland to remain analogous to that of the unablated controls. The androgenic gland of control crabs during revival phase (January-February) was discerned with a few patches of proliferated type I cells scattered among vacuoles and degenerating cells. The most prominent feature of the gland of bilaterally ablated crabs during revival phase was the extensive proliferation of type I cells. Not much significant change was observed in the morphology and histology of the gland of unilaterally ablated crabs of revival phase.

The current study examined the moultwise impact of unilateral eyestalk ablation on major biochemical parameters of the muscle of the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae). Meat from unilaterally destalked crabs 15 days post-operation was analyzed for protein, oligosaccharide, polysaccharide, total free amino acid, total lipid, cholesterol and moisture content following standard procedures. The results indicated a moultwise cycling of the major biochemical parameters of the muscle. Unilateral eyestalk ablation induced a rise in all the major biochemical parameters except moisture, irrespective of the moult stages. The alteration induced as an impact of unilateral destalkation in the biochemical parameters decide the suitability of this technique to enhance meat quality as practiced in aquaculture farms of marine decapods.

Article corrigendum.