Molt Stage Research Articles

Non‐breeding Cackling, Ross's and Snow Geese on Baffin Island show no loss of body mass during wing moult

Non‐breeding Cackling Branta hutchinsii, Ross's Anser rossii and Lesser Snow Geese Anser caerulescens caerulescens captured during remigial moult on Baffin Island in 2015 showed no loss of body mass with moult stage, and individual variation in mass was largely explained by sex and measures of body size (tarsus length). Exceptional conditions in 2015 resulted in almost no reproductive effort or success in that year, so captured geese of all three species were likely to have been non‐breeding individuals that initiated moult early, whereas there were almost no failed or successful breeders, which would normally moult later. This suggests that in a non‐breeding year (i.e. in the absence of competition from large numbers of goslings), locally moulting geese can obtain sufficient exogenous energy to meet their needs during the flightless wing moult period without losing body mass. This also is consistent with the hypothesis that in other species of geese, accumulation of fat stores prior to, and depletion of such stores during, wing moult is adaptive and likely to be a feature of individual plasticity to meet particular needs, such as undertaking moult migration to remote sites where precise foraging and predation conditions cannot be anticipated, or where competition from more dominant individuals may restrict their access to a reliable food supply.

Histomorphometric and transcriptomic features characterize silk glands' development during the molt to intermolt transition process in silkworm

The molt–intermolt cycle is an essential feature in holometabolous and hemimetabolous insects' development. In the silkworm, silk glands are under dramatic morphological and functional changes with fibroin genes' transcription being repeatedly turned off and on during the molt–intermolt cycles. However, the molecular mechanisms controlling it are still unknown. Here, silk gland's histomorphology and transcriptome analysis were used to characterize changes in its structure and gene expression patterns from molt to intermolt stages. By using section staining and transmission electron microscope, a renewable cell damage was detected in the silk gland at the molt stage, and an increased number of autophagosomes and lysosomes were found in silk gland cells' cytoplasm. Next, by using RNA sequencing, 54,578,413 reads were obtained, of which 85% were mapped to the silkworm reference genome. The expression level analysis of silk protein genes and silk gland transcription factors revealed that fibroin heavy chain, fibroin light chain, P25/fhx, sericin1, sericin3 and Dimm had consistent alteration trends in temporal expression. In addition, differentially expressed genes (DEGs) were identified, and most of the DEGs associated with ecdysone signal transduction, mRNA degradation, protein proteolysis, and autophagy were significantly down-regulated in the transition from molt to intermolt, suggesting that these pathways were activated for the silk gland renewal. These findings provide insights into the molecular mechanisms of silk gland development and silk protein genes transcriptional regulation during the molt to intermolt transition process.

Mineral in skeletal elements of the terrestrial crustacean Porcellio scaber: SRμCT of function related distribution and changes during the moult cycle

Terrestrial isopods moult first the posterior and then the anterior half of the body, allowing for storage and recycling of CaCO3. We used synchrotron-radiation microtomography to estimate mineral content within skeletal segments in sequential moulting stages of Porcellio scaber. The results suggest that all examined cuticular segments contribute to storage and recycling, however, to varying extents. The mineral within the hepatopancreas after moult suggests an uptake of mineral from the ingested exuviae. The total maximum loss of mineral was 46% for the anterior and 43% for the posterior cuticle. The time course of resorption of mineral and mineralisation of the new cuticle suggests storage and recycling of mineral in the posterior and anterior cuticle. The mineral in the anterior pereiopods decreases by 25% only. P. scaber has long legs and can run fast; therefore, a less mineralised and thus lightweight cuticle in pereiopods likely serves to lower energy consumption during escape behaviour. Differential demineralisation occurs in the head cuticle, in which the cornea of the complex eyes remains completely mineralised. The partes incisivae of the mandibles are mineralised before the old cuticle is demineralised and shed. Probably, this enables the animal to ingest the old exuviae after each half moult.

First records of lyre crab <i>Hyas lyratus </i>Dana, 1851 (Decapoda: Majidae) in the Russian waters (northwestern Bering Sea) and some features of its biology

Males and females of lyre crab Hyas lyratus were found in the northwestern Bering Sea in 2010 (late July - early August), for the first time in the Russian waters. The crabs were caught during the trawl survey by bottom trawl at the depth of 111-169 m, on mixed grounds. Crabs of this species were caught again in the same area in August 2012. Thus, new western limit of the species distribution area is established as the western vicinity of Cape Navarin (61 о 52′ N 177 о 51′ E). Size of males was 35-43 mm, size of females varied within the range 19-49 mm. All males were at the 3 rd molting stage in 2010 and at the 3 rd terminal stage in 2012. All females, except one juvenile, had eggs of orange color. Traumatism (autotomy) of crabs was insignificant. Biological parameters of the crabs from the northwestern Bering Sea are compared with those from the Salish Sea (North-East Pacific).

Seasonal variation and annual trends of metals and metalloids in the blood of the Little Penguin (Eudyptula minor)

Little Penguins (Eudyptula minor) are high-trophic coastal feeders and are effective indicators of bioavailable pollutants in their foraging zones. Here, we present concentrations of metals and metalloids in blood of 157 Little Penguins, collected over three years and during three distinct seasons (breeding, moulting and non-breeding) at two locations: the urban St Kilda colony and the semi-rural colony at Phillip Island, Victoria, Australia. Penguin metal concentrations were foremostly influenced by location (St Kilda>Phillip Island for non-essential elements) and differed among years and seasons at both locations, reflecting differences in seasonal metal bioaccumulation or seasonal exposure through prey. Mean blood mercury concentrations showed an increasing annual trend and a negative correlation with flipper length at St Kilda. Notably, this study is the first to report on blood metal concentrations during the different stages of moult, showing the mechanism of non-essential metal mobilisation and detoxification.

The seasonal glucocorticoid response of male Rufous-winged Sparrows to acute stress correlates with changes in plasma uric acid, but neither glucose nor testosterone

We sought to clarify functional relationships between baseline and acute stress-induced changes in plasma levels of the stress hormone corticosterone (CORT) and the reproductive hormone testosterone (T), and those of two main metabolites, uric acid (UA) and glucose (GLU). Acute stress in vertebrates generally stimulates the secretion of glucocorticoids, which in birds is primarily CORT. This stimulation is thought to promote behavioral and metabolic changes, including increased glycemia. However, limited information in free-ranging birds supports the view that acutely elevated plasma CORT stimulates glycemia. Acute stress also often decreases the secretion of reproductive hormones (e.g., T in males), but the role of CORT in this decrease and the contribution of T to the regulation of plasma GLU remain poorly understood. We measured initial (pre-stress) and acute stress-induced plasma CORT and T as well as GLU in adult male Rufous-winged Sparrows, Peucaea carpalis, sampled during the pre-breeding, breeding, post-breeding molt, and non-breeding stages. Stress increased plasma CORT and the magnitude of this increase did not differ across life history stages. The stress-induced elevation of plasma CORT was consistently associated with decreased plasma UA, suggesting a role for CORT in the regulation of plasma UA during stress. During stress plasma GLU either increased (pre-breeding), did not change (breeding), or decreased (molt and non-breeding), and plasma T either decreased (pre-breeding and breeding) or did not change (molt and non-breeding). These data provide only partial support to the hypothesis that CORT secretion during acute stress exerts a hyperglycemic action or is responsible for the observed decrease in plasma T taking place at certain life history stages. They also do not support the hypothesis that rapid changes in plasma T influence glycemia.

Gut microbial communities associated with the molting stages of the giant freshwater prawn Macrobrachium rosenbergii

The reciprocal interaction between host organisms' physiology and their gut microorganism community is of great interest in aquatic animal biology and aquaculture but for crustaceans, it remains understudied. This study enhances our understanding of this community of microorganisms as it changes during the molt cycle. Because crustaceans shed a major component of their gut, and the associated microbiome, with each molt this adds a level of complexity heretofore unexamined. We have identified the bacterial communities that are affected by the changing gut environment and that may in turn, exert some control over aspects of the molt cycle. We investigated the structural changes of the resident gut bacterial communities, using the diversity of the 16S rRNA gene by 454 pyrosequencing, in the freshwater prawn Macrobrachium rosenbergii during its four-stage molt cycle. The number of bacterial operational taxonomic units (OTUs) increased from stages A to C. Stage C the intermolt and longest lasting stage was different in the gut bacterial community structure having the (a) highest number of total OTUs, (b) highest number of unique and newly introduced OTUs, (c) highest percentage of estimated specialists OTUs, i.e. that are more ecologically restricted. Moreover, stage C was characterized by greater contribution of Actinobacteria-related and unaffiliated OTUs. The most dominant OTUs found in stage C of the gut of M. rosenbergii were related to microorganisms involved in fermentation and food material processing originating from similar, i.e. gut, or habitats of terrestrial and freshwater animals. Thus, the distinct gut bacterial communities found in molting stage C corroborate with the physiological significance of this molting stage. The abiotic factors and the exact role of the corresponding specific bacterial communities in the animal's physiology and growth are areas that remain to be elucidated. Statement of relevanceA thorough understanding of M. rosenbergii digestive physiology is essential to achieve better growth performance when cultured. This paper provides information that could be useful for developing effective strategies to manipulate gut microbial communities to promote prawn's growth and health and improve aquaculture productivity.

Comparative analysis of the integument transcriptomes of the black dilute mutant and the wild-type silkworm Bombyx mori.

The insect cuticle is a critical protective shell that is composed predominantly of chitin and various cuticular proteins and pigments. Indeed, insects often change their surface pigment patterns in response to selective pressures, such as threats from predators, sexual selection and environmental changes. However, the molecular mechanisms underlying the construction of the epidermis and its pigmentation patterns are not fully understood. Among Lepidoptera, the silkworm is a favorable model for color pattern research. The black dilute (bd) mutant of silkworm is the result of a spontaneous mutation; the larval body color is notably melanized. We performed integument transcriptome sequencing of the wild-type strain Dazao and the mutant strains +/bd and bd/bd. In these experiments, during an early stage of the fourth molt, a stage at which approximately 51% of genes were expressed genome wide (RPKM ≥1) in each strain. A total of 254 novel transcripts were characterized using Cuffcompare and BLAST analyses. Comparison of the transcriptome data revealed 28 differentially expressed genes (DEGs) that may contribute to bd larval melanism, including 15 cuticular protein genes that were remarkably highly expressed in the bd/bd mutant. We suggest that these significantly up-regulated cuticular proteins may promote melanism in silkworm larvae.

Moult-inhibiting fusion protein augments while polyclonal antisera attenuate moult stages and duration in Penaeus monodon

Moulting in crustaceans is regulated by moult-inhibiting hormone (MIH) of the CHH family neuropeptides. The inhibitory functions of MIH have pivotal roles in growth and reproduction of Penaeus monodon. In this study, we report the expression of a thioredoxin-fused mature MIH I protein (mf-PmMIH I) of P. monodon in a bacterial system and its use as antigen to raise polyclonal antiserum (anti-mf-PmMIH I). The mature MIH I gene of 231bp, that codes for 77 amino acids, was cloned into the Escherichia coli thioredoxin gene fusion expression system. The translation expression vector construct (mf-PmMIH I+pET32a+) upon induction produced 29.85kDa mature MIH I fusion protein (mf-PmMIH I). The purified fusion protein was used as exogenous MIH I and as antigen to raise polyclonal antisera. When fusion protein (mf-PmMIH I) was injected into D2 and D3 stages of juvenile shrimp, the moult cycle duration was extended significantly to 16.67±1.03 and 14.67±1.03days respectively compared to that of 11.67±1.03days in controls. Moult duration was further reduced to 8.33±0.82days when polyclonal antiserum (anti-mf-PmMIH I – 1:500 dilutions) was injected. Anti-mf-PmMIH I immunolocalized MIH I producing neurosecretory cells in the eyestalk of P. monodon. In short, the present manuscript reports an innovative means of moult regulation in P. monodon with thioredoxin fused MIH I and antisera developed.

First predation record ofCanthecona furcellata(Wolff.) (Hemiptera: Pentatomidae) on spinning stage silkwormAntheraea mylitta(Drury)

AbstractA new scientific survey elucidates the preferred attack of stink bugCanthecona furcellata(Wolff.) (Hemiptera: Pentatomidae) on the spinning stage of the tropical tasar silkworm,Antheraea mylitta(Drury) (Lepidoptera: Saturniidae). The silkwormA. mylittaproduces an excellent quality of wild silk; however, due to predation byC. furcellata, tasar silk production is reduced. The bugC. furcellatais the most invasive larval predator ofA. mylittaand predation is high during early instars as well as the molting stage of the larvae. However, for the first time it is reported that the spinning stage is also preferable for attack by the stink bug. Both the nymphs and adults ofC. furcellataattack the spinning silkworm; moreover, stink bug attack is observed in groups under field conditions. It is postulated that feeding preference is due to the concealed, non‐movable and less defensive stage of the tasar larvae during spinning. The predation ofC. furcellataincludes its approach on target larva of the tasar silkworm during spinning, where it inserts the proboscis inside the larval skin through the moist silk network of newly forming or formed cocoon. Most of the spinning larvae die from the attack and the normal seed cocoon fails to form. The mechano‐ and chemoreceptors, present on the antenna and proboscis ofC. furcellata, play an important role in prey locating and the feeding mechanism. The life cycle ofC. furcellatais also discussed in the present study.

Multiprotein bridging factor 2 regulates the expression of the fibroin heavy chain gene by interacting with Bmdimmed in the silkworm Bombyx mori.

Multiprotein bridging factor 2 (MBF2) was first isolated from the posterior silk gland of Bombyx mori. However, its function in B.mori is still unknown. Herein, MBF2 transcripts were detected mainly in the posterior silk gland and Malpighian tubules of B.mori larvae via a quantitative PCR analysis. An analysis of temporal expression patterns showed that the expression pattern of MBF2 was the opposite of that of the fibroin heavy chain (fibH) gene, as its expression was high during the fourth-instar moulting stage, decreased gradually during the fifth-instar feeding stage and disappeared at the end of the fifth-instar phase. Furthermore, bimolecular fluorescent complementation and Far-Western blot assays showed that MBF2 interacted with the basic helix-loop-helix transcription factor Bmdimmed. Dual luciferase reporter assays showed that MBF2 down-regulated the promoter activity of fibH and inhibited the effect of Bmdimmed (Bmdimm) on fibH expression. MBF2 expression was induced in silk glands after treatment with 20-hydroxyecdysone in vivo and in vitro. These findings suggest that MBF2 is a transcriptional repressor that is involved in controlling the regulation of the fibH gene in the posterior silk gland by interacting with Bmdimm.

Mutation of a Cuticle Protein Gene, BmCPG10, Is Responsible for Silkworm Non-Moulting in the 2nd Instar Mutant.

In the silkworm, metamorphosis and moulting are regulated by ecdysone hormone and juvenile hormone. The subject in the present study is a silkworm mutant that does not moult in the 2nd instar (nm2). Genetic analysis indicated that the nm2 mutation is controlled by a recessive gene and is homozygous lethal. Based on positional cloning, nm2 was located in a region approximately 275 kb on the 5th linkage group by eleven SSR polymorphism markers. In this specific range, according to the transcriptional expression of thirteen genes and cloning, the relative expression level of the BmCPG10 gene that encodes a cuticle protein was lower than the expression level of the wild-type gene. Moreover, this gene’s structure differs from that of the wild-type gene: there is a deletion of 217 bp in its open reading frame, which resulted in a change in the protein it encoded. The BmCPG10 mRNA was detectable throughout silkworm development from the egg to the moth. This mRNA was low in the pre-moulting and moulting stages of each instar but was high in the gluttonous stage and in newly exuviated larvae. The BmCPG10 mRNA showed high expression levels in the epidermis, head and trachea, while the expression levels were low in the midgut, Malpighian tubule, prothoracic gland, haemolymph and ventral nerve cord. The ecdysone titre was determined by ELISA, and the results demonstrated that the ecdysone titre of nm2 larvae was lower than that of the wild-type larvae. The nm2 mutant could be rescued by feeding 20-hydroxyecdysone, cholesterol and 7—dehydrocholesterol (7dC), but the rescued nm2 only developed to the 4th instar and subsequently died. The moulting time of silkworms could be delayed by BmCPG10 RNAi. Thus, we speculated that the mutation of BmCPG10 was responsible for the silkworm mutant that did not moult in the 2nd instar.

Haemolymph constituents and osmolality as functions of moult stage, body weight, and feeding status in marron, Cherax cainii () and yabbies, Cherax destructor (Clark, 1936).

The study investigates the change in osmolality and haemolymph constituents in marron Cherax cainii and yabbies Cherax destructor associated with moult stages, body weights and their feeding status. A total of 582 haemolymph samples from 5 moult stages (postmoult-AB, intermoult-C, and premoult stages – D0, D1, D2), two body weight classes (2–15 g and 61–75 g) and nutritional status were used for analysis of osmolality, protein, glucose, and ionic concentrations of potassium and chloride following the standard biochemical procedures. The haemolymph protein, glucose, potassium and chloride levels were highest at intermoult and early premoult stages, and lowest at postmoult in both crayfish species. Except protein, no significant differences were seen in analyzed parameters between various weight classes and two species. Haemolymph osmolality, protein and glucose were significantly higher in fed crayfish, whereas no variations in haemolymph potassium and chloride concentrations were observed between the fed and unfed crayfish. Maximum osmolality was recorded at 7–8 h after feeding in both crayfish species. The results showed that the biochemical changes in the haemolymph of marron and yabbies are related to moult stages, body weight and feeding and thus can be used as tools for determining suitable diets.

Susceptibility of Tiger Shrimp (Panaeus monodon) against Vibrio harveyi on various Molt Stage and Osmolarity

Vibrio harveyi causes disease of tiger shrimp (Penaeus monodon) aquaculture in East Kalimantan. This research aimed to investigate the susceptibility of tiger shrimp on various molt stage and osmolarity, and determine the salinity (osmolarity) of water that can reduce the risk of V. harveyi attack. Shrimp age of 1.5 months was maintained in 4 aquariums with salinity 29.72 ‰, 26.07 ‰, 22.35 ‰ and 17.79 ‰, then challenged with V. harveyi. After 7 and 14 days, osmolarity of haemolimph was observed with automatic osmometer and Digital Roebling Osmometer. The susceptibility of tiger shrimp to V. harveyi was evaluated based on clinical symptoms, pathological anatomy of shrimp and density of V. harveyi (TPC) in the hepatopancreas. Osmolarities of shrimp haemolymph at premolt, postmolt, and intermolt stage were 575.30-812.60; 534.00-788.80, and 566.20-795.60 mOsm/l H2O, respectively. The lowest bacterial content in the premolt stage was maintained at a salinity 22.35 ‰, and the highest one was obtained in postmolt stage at 29.72 ‰. The molting and postmolt stage were the most susceptible to V. harveyi attacks. The results suggested that the shrimp maintained at 22.35 ‰ salinity was less susceptible to V. harveyi.

Plasticity in moult speed and timing in an arctic‐nesting goose species

Environmental constraints are strong in migratory species that breed in the Arctic. In addition to breeding, Anatidae have to renew all their flight feathers during the short arctic summer. We examine how temporal constraints and climate affect the phenology of flight feather moult in the greater snow gooseChen caerulescens atlantica, a High Arctic nesting species. We used a database of 1412 moulting adult females measured over 15 yr on Bylot Island, Nunavut. Ninth (9th) primary length was used to determine the moult stage and speed of feather growth. We found a positive relationship between median annual hatching and moult initiation dates and the slope did not differ from 1. The interval between hatching and moult initiation was thus rather fixed and geese did not initiate moult earlier when reproductive phenology was delayed. Nonetheless, there was no relationship between median hatching date and the date at which birds regained flight capacity, suggesting that date of end of moult is independent of the reproductive phenology. There was a trend for an increase in the speed of flight feather growth in years with delayed hatching date. This is the most likely mechanism that could explain moult phenology adjustment in this species. Finally, we found a positive relationship between 9th primary length (corrected for inter‐annual variations) and body condition, suggesting a delay in moulting for individuals in poor condition. These results suggest that moult plasticity is primarily governed by variations in feather growth speed. This phenotypic plasticity could be necessary to complete flight feather renewal before the end of the arctic summer, independently of reproductive phenology and spring environmental conditions. Our novel results suggest possible phenological adjustments through moult speed, which was considered constant in geese until now.

Combination of At-Sea Activity, Geolocation and Feather Stable Isotopes Documents Where and When Seabirds Molt

Key facets of the foraging ecology of seabirds during the inter-breeding period still remain poorly understood because of the difficulty of studying them at sea, including during the energy-demanding moulting stage. Here, the extent to which three sympatric petrels (Antarctic and thin-billed prions, and blue petrel) from the subantarctic Kerguelen Islands modify their foraging ecology during moult was investigated using a combination of complementary tools, namely miniaturized saltwater immersion geolocators (GLS) and the isotopic method. Firstly, moulting behaviour was first characterized in the blue petrel, a reference species that is known to renew its plumage in autumn. GLS and feather stable isotopes (13C as a proxy of the birds’ foraging habitat) indicated that the post-breeding moult of blue petrel occurred in Antarctic waters. Importantly, activity recorders showed that moult was marked by a strong peak in time spent daily sitting on water, which thereafter declined to lower values during the remaining winter months. Secondly, the peak in time spent sitting on water was used as a proxy to characterize the contrasted moult strategies of the two prion species. As blue petrels demonstrated, thin-billed prions moulted during the post-breeding period in cold Antarctic waters where they fed primarily on low trophic level prey, most likely Antarctic krill (15N as a proxy of the birds’ diet). By contrast, Antarctic prions presented an unexpected pre-breeding moult of longer duration that took place further north, in warm subtropical waters. Interestingly, the two Antarctic moulting species, the blue petrel and thin-billed prion, renewed their plumage at the same time and within the same oceanic zone that is likely to be a previously undescribed hot spot of seabird diversity during the Austral autumn. The study contributes to a growing body of evidence that closely-related species exhibit various foraging strategies allowing ecological segregation and sheds new light on the poorly known critical moulting stage of seabirds.

Infestation by the epibiont Octolasmis lowei in a portunid crab assemblage from a subtropical coast

We investigated the infestation by Octolasmis lowei Darwin, 1851 in branchial chambers of the portunid Achelous spinimanus (Latreille, 1819), Arenaeus cribrarius (Lamarck, 1818), Callinectes danae Smith, 1869, and Callinectes ornatus Ordway, 1863. We evaluated how infestation is related to host maturity, molt stage, carapace width and sex. The infestation probability increases with host carapace width, and infested crabs were more likely to be adults in intermolt stage. Infestation prevalence did not differ between sexes, except for C. ornatus, in which females had higher infestation than males. Infestation intensity was higher for males than females in A. cribrarius and A. spinimanus, while C. ornatus showed an opposite pattern. Association of O. lowei with portunid seems to be tightly related to the biological traits of its host. Some of these traits, such as host size, maturity and molt stage, are likely to affect infestation in a similar way for all host species, while the effect of other traits, such as sex identity, seems to vary among hosts. We suggest a deeper understanding of the factors driving host use by generalist epibionts such as O. lowei depends on investigating their occurrence on a variety of potential hosts, as well as performing manipulative studies to evaluate the factors driving host preferences by this epibiont.

Natural and Induced (Eyestalk Ablation) Molt Cycle in Freshwater Rice Field Crab Oziothelphusa Senex Senex

In crustaceans, molting is the process of shedding old exoskeleton and is required for the somatic growth of new exoskeleton for its growth. The molting processes in crustaceans vary from one species to other and also vary with the environmental conditions. In the present study the molt cycle of freshwater crab Oziothelphusa senex senex was studied. The size of crabs selected for the study is 30 ± 2 g. The natural molt cycle is consisting of intermolt (C1, C2, C3 and C4), premolt (D1, D2, D3 and D4), ecdysis (E) and post molt (A1, A2, B1 and B2) stages were measured and the percentage of each stage in the molt cycle was calculated. The biggest stage in the O. senex senex molt cycle is intermolt stage (90.0%) and shortest one is ecdysis (0.01%). Induced molt cycle was studied by eyestalk extirpation (ESX) and observed that 60.71% of male crabs and 52.0% female crabs were molted after 28th day of extirpation suggesting the role of eyestalk principle in regulating the molting process.

Impact of unilateral eyestalk ablation on major biochemical parameters of muscle of the freshwater crab Travancoriana schirnerae Bott, 1969 (Decapoda: Gecarcinucidae)

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.

Cannibalism among Lithodes santolla (Molina 1782) juveniles: effect of stocking density, stage and molt condition

Losses of king crabs (deaths) in massive rearing conditions are frequently attributed to cannibalism. As several factors could influence cannibalism intensity during culture, the aim of the present study was to determine the effect of molt condition, stage and density on cannibalism among Lithodes santolla juveniles. Comparisons between intermolt and molt conditions and between C1 and C2 stages during intermolt were performed at three densities (6, 12 and 18 individuals per flask; that is equivalent to 236, 472 and 708 individuals m−2). After 16 days of juvenile coexistence, cannibalism (injured + dead) was higher during molting (33.9 ± 4.5 %) than intermolt (21.7 ± 3.9 %), even though only 36 % of crabs had molted. Although cannibalism was similar in C1 and C2 stages, the proportion of dead animals was higher by a factor of three in C1 stage, probably due to the fact that animals reach the first juvenile stage with low energetic reserves, after the lecithotrophic larval development. Density was the main factor influencing cannibalism in our experiments. Higher densities promoted higher deaths, while agonistic interactions evidenced by injured crabs remained constant. Walking appendages were lost more often than chelipeds during first agonistic encounters. We recommend the use of intermediate densities (450 crabs m−2 at most), the early detection of exuviae and the sorting of crabs after molting, for L. santolla rearing.