Continuous moulting by Antarctic krill drives major pulses of carbon export in the north Scotia Sea, Southern Ocean

Antarctic krill play an important role in biogeochemical cycles and can potentially generate high-particulate organic carbon (POC) fluxes to the deep ocean. They also have an unusual trait of moulting continuously throughout their life-cycle. We determine the krill seasonal contribution to POC flux in terms of faecal pellets (FP), exuviae and carcasses from sediment trap samples collected in the Southern Ocean. We found that krill moulting generated an exuviae flux of similar order to that of FP, together accounting for 87% of an annual POC flux (22.8 g m−2 y−1). Using an inverse modelling approach, we determined the krill population size necessary to generate this flux peaked at 261 g m−2. This study shows the important role of krill exuviae as a vector for POC flux. Since krill moulting cycle depends on temperature, our results highlight the sensitivity of POC flux to rapid regional environmental change.

Gonadal maturation, fecundity and hatching performance of wild caught tiger shrimp Penaeus monodon using unilateral eyestalk ablation in captivity

In this study, the effects of eyestalk ablation on maturation, moulting, spawning and hatching rate of wild caught Penaeus monodon were investigated. Twenty males (M) and 30 eyestalk–ablated and 30 non–ablated females (F), all individually marked (M: F=1:3) were stocked into two 15–ton capacity (each) maturation tank. All the ablated females moulted in 7.92±0.24 (mean±standard error) days, and first spawning occurred 3.2±0.20 days following eyestalk ablation. While twenty-five ablated females spawned, producing an average of 296,160±26,589 eggs, only eight non–ablated females spawned, producing an average of 195,462±20,565 eggs during the investigation period of 120 days. A significant positive correlation between fecundity and female body weight (P<0.05; P<0.001) was observed. Throughout the experiment, the average number of spawning per female was 1.8±0.14 for ablated and one for non–ablated females. Multiple spawning (up to three times) occurred within the same moulting cycle in ablated females. Among the ablated P. monodon females, 36% spawn once, 48% second time, and 16% third time. The average fertility rate of the eggs was high, ranging between 80 and 90% in non-ablated females, while in ablated females; the range was between 72 and 88% and differ significantly (p<0.05) ablated and non ablated females. Average hatching rate ranges between 70 and 80% for ablated and 75 and 82% for non-ablated females (p<0.05). From eggs to nauplii production per female was 167,838 for ablated and 127,500for non–ablated females. This study indicates that eyestalk ablation and environmental condition were important inducing tools for re-maturation of spent P. monodon that continued supply of seed stock for effective commercial shrimp farming.J. Bangladesh Agril. Univ. 13(2): 315-322, December 2015

cDNA cloning, characterization and mRNA expression of cryptocyanin from the Chinese mitten crab, Eriocheir sinensis H. Milne Edwards, 1853

Cryptocyanin is a copper-free non-respiratory protein and plays an important role in the physiological process of decapod crustaceans. In the present study, the full length cDNA encoding cryptocyanin (EsCc) was cloned from the haemocytes of the Chinese mitten crab Eriocheir sinensis, which was 2630 bp, consisting of a 5′-untranslated region of 237 bp, a 3′-untranslated region of 359 bp, and an open reading frame of 2034 bp. The deduced protein possessed 678 amino-acid residues, and the predicted molecular mass was 79.09 kDa. The phylogenetic analysis revealed that it belonged to the arthropod haemocyanin superfamily and shared 78% homology to Dungeness crab Metacarcinus magister cryptocyanin subunit 2. The expression pattern of EsCc in five tissues was investigated in premoult, intermoult and postmoult stages to understand its role during the moulting cycle. In hepatopancreas, the significant up-regulation of EsCc expression was observed in both premoult and intermoult stages, while the significant change of EsCc expressions in muscle and haemocytes was only found in premoult stages. To gain insight into the antimicrobial activity of EsCc in inflammatory processes, its expression profiles in the haemolymph of Chinese mitten crab challenged with Vibrio anguillarum and Pichia pastoris were examined. The challenge of V. anguillarum induced higher expression of EsCc as early as 6 h post-infection. Instead, a significant up-regulation of EsCc transcript was observed at 12 h post P. pastoris challenge. The above results implied that crustacean cryptocyanin was involved in the new exoskeleton formation. Also, it might be induced to resist invasions of pathogens.

Molecular cloning, characterization and expression analysis of the retinoid X receptor in the swimming crab, Portunus trituberculatus (Miers, 1876) (Decapoda, Portunidae)

To elucidate the role of the retinoid X receptor (RXR) in moulting and ovarian development of crustaceans, the full-length cDNA of RXR (PtRXR) in Portunus trituberculatus (Miers, 1876) was cloned by nested reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The cDNA sequence of PtRXR was determined to be 1365 bp in length and contained an open reading frame (ORF) of 1140 bp encoding a 379-amino-acid residue protein. The deduced amino-acid sequence of PtRXR shared high identities with other known RXRs. Phylogenetic analysis showed that PtRXR was clustered among crustacean RXRs and located closer to the vertebrate RXRs than the insect ultraspiracle (USP, an orthologue of RXR). Quantitative real-time PCR (qRT-PCR) was used to analyse the tissue distribution of PtRXR and its expression patterns during the moulting cycle and the second ovarian development of P. trituberculatus. The results showed that PtRXR was widely distributed in the tested tissues. PtRXR mRNA levels were significantly high in ovary and Y-organs (YO) of intermoult crabs. The mRNA levels of PtRXR in YO and mandibular organs (MO) decreased significantly from intermoult to premoult. In addition, PtRXR was expressed at each stage of the second ovarian development in ovary, hepatopancreas, YO and MO, and the expression levels reached maximal values when the ovary reached the final stage of maturation. These results indicate that PtRXR might have an important role in regulating the moulting and ovarian development of P. trituberculatus.