Large Crabs Research Articles

Impact of steaming and peeling on the weight loss in blue swimming crabs in Pangkajene Islands, South Sulawesi

Abstract The blue swimming crab (Portunus pelagicus) is an important fishery resource in Indonesia because it has a high value and involves a lot of human resources. The pasteurized crab goes through several main stages, namely steaming, stripping, and canning. Steamed crabs will experience weight loss and produce a yield of meat in a certain amount and composition after peeling. This study aims to determine the weight loss during crab steaming and stripping processes on different sizes of crabs. The crabs were classified into three categories, namely small crab (carapace width <10 cm), big crab (carapace width >10 cm), and egg-berried female crabs. Technically, crabs were steamed for 20 minutes after the water boils with temperature of steaming of 80–90 °C. Steaming process wereallowed to stand for 60 minutes, followed by. peeling process where crab meat were separated from the skin. Weight measurements were taken on fresh, warm (shortly after steaming), and cooked crab (adjusted to room temperature) to calculate weight loss due to steaming while considering temperature adjustments and total loss. Results revealed the weight decrease about 16.75% during steaming, 19.61% during relaxation, and 27.47% during overall process. The highest meat yield was obtained from small crab by 30.64%, followed by large crab by 27.25%, and egg berried female by 24.39%.

Risk analysis of crab peeling business: a case study at miniplant Medan I Deli Serdang

Abstract Portunus pelagicus also known as also known as the blue crab, blue swimmer crab, blue manna crab or sand crab is a species of large crab found in the Indo-Pacific, including off the coasts of Indonesia. The crab peeling industry represents an attractive business opportunity in the seafood sector, with growing demand for processed crab meat. Miniplant Medan I is a business located in north Sumatra which specializing in crab peeling to obtain quality crab meat. However, like any business venture, it is not without its inherent risks. This study aims to identify, assess, and evaluate potential risks, uncertainties, and hazards that can affect the crab peeling business Miniplant Medan I. Risk measurement in this study is carried out using the PIM (Probability Impact Matrix) method. The result shows that the highest risk factors in the Miniplant Medan I business are overexploitation of crab’s eggs and small sizes crab, employee negligence in the use of prohibited cosmetic ingredients, use of low-quality raw materials, cold chain disconnection, lack of employee and equipment sanitation.

Patterns in abundance, size and space‐use of Giant Mud Crab (Scylla serrata) in a temperate marine protected area

Abstract Marine Protected Areas limit fishing to protect a broad range of species and enhance biodiversity. Consequently, closures may not benefit species equally and species‐specific assessments are required to determine the impact of closures. Relative abundance and size of Giant Mud Crab (Scylla serrata) was compared across no‐take and fished zones in Port Stephens‐Great Lakes Marine Park, on the temperate east coast of Australia (32.45°S). In addition, passive acoustic telemetry was used to estimate daily space‐use areas. Similar abundances were observed between no‐take and fished zones; however certain no‐take sites had higher abundances than others. In addition, crabs were 9.9 mm larger in no‐take zones on average. Daily crab space‐use varied widely (~4 to 1000 m2), and generally increased with water temperature and conductivity. These patterns indicate that recruitment processes interact with marine park protection to shape crab abundances across estuaries. However no‐take zoning appears to primarily limit fishing mortality on legal size crabs (i.e., carapace length >85 mm) resulting in larger crabs within no‐take zones. This may mean no‐take zones enhance reproductive output of crab populations since larger individuals are likely to be more fecund.

The Complete Genome Sequence of Portunus pelagicus (Portunidae, Decapoda), the Blue Swimming Crab.

Portunus pelagicus is a large crab found in the Indo-Pacific. We present the whole genome sequence of this species. Illumina paired-end reads were assembled by a de novo method followed by a finishing step. The raw and assembled data are publicly available via GenBank: Sequence Read Archive (SRR25655135) and assembled genome (JAWWMC000000000).

Microplastics in the Gastrointestinal Tract of Blue Crab (Portunus pelagicus) Caught by Bandaran, Bangkalan Fishermen at Different Sizes

Microplastics are plastic waste that is degraded into small sizes that float in water bodies and can be ingested by aquatic biota. This study aims to determine the shape, color, and abundance of microplastics in the digestive tract of blue swimming crab (Portunus pelagicus) caught by fishermen in Bandaran Village, Bangkalan at different sizes. Swimming crab sampling was carried out 3 times with different sizes, namely small, medium, and large. Identification of microplastics using a solution of H2SO4 and H2O2 with a concentration of 30% with a ratio of 3:1. Microplastic forms found include fiber, fragments, and films. The highest abundance of microplastics was found in large crabs with a value of 3.13 particles/g. The simple regression test results obtained a relatively small R² value of 0.0003 meaning that the size of the crab has a very small correlation with the abundance of microplastics in the digestive tract.

Modification of Eco-Friendly Collapsible Crab Pot of Blue Swimming Crab in Pangkep Regency, Indonesia

The aim of this study is to determine the effect of mesh size on the catches of small crab (Portunus sp.) both in number, carapace length (CL), and catchability between modified and control collapsible crab pot. This study used mesh size of the wrapping net (PE) from 2.5 cm (± 1 inch) to 7.0 cm (± 2.5 inches) with 20 units and 20 repetitions (trips). The results showed that different mesh size has a significant effect on the catch of the pot. However, the catch of a 2.5-inch mesh size- showed a larger carapace length = 42 individuals (85.7 %), while the escaped number was 44 individuals (63.7%) in the unfeasible category catch while the remaining 25 samples (36.2%) are eligible to catch. The Anova test on the catch of crab pot with a mesh size of 2.5 inches and 1 inch based on CL showed F-count > F_table (54.213 > 3.016) or sig. value <0.05 (0.00<0.05) which means that the size of the crab pot had a significant effect on CL. This identified that the size of the collapsible crab pot with a mesh size of 2.5 inches could pass small crabs and can only catch large crabs.

Intertidal habitat complexity influences the density of the non-native crab Hemigrapsus sanguineus.

Habitat structural complexity can provide protection from predators, potentially affecting population density of native and non-native prey. The invasive Asian shore crab, Hemigrapsus sanguineus, occurs in variable densities in the rocky intertidal zone of eastern North America and northern Europe, often in densities greater than in its native range. The present study examined the influence of habitat complexity on the density of H. sanguineus. Artificial shelters of concrete pavers with stones arranged in increasing complexity were deployed in the intertidal zone along a rocky shore in southeastern Massachusetts, USA, for 21 consecutive weekly intervals in 2020. Crabs consistently reached the highest densities in the most complex shelters despite their lower internal surface area. In addition, crabs exhibited shelter selectivity based on body size, with large crabs occupying artificial shelters in greater numbers than adjacent natural substrate. In a subsequent lab study, crab activity over 1 h was observed in the presence of the same artificial shelters, under simulated tidal conditions. Shelter complexity had little influence on the number of crabs under the pavers although crabs were more active when submerged in water than exposed to air. These results show that crab density increases as habitat complexity increases, and complexity may serve as a predictor of H. sanguineus density but not short-term behavior.

Trapezia Crabs That Dwell in Distinctive Day/Night Canopy Compartments of a Marine Animal Forest, Forage on Demersal Plankton

Canopies of branching corals harbor a wide range of sessile- and mobile-dwelling species that benefit from the physical compartments and the micro-environments created by the complex three-dimensional structures. Although different compartments within canopies are differentially used by inhabitant species, the distribution of mobile animals between coral canopy compartments are not fully explored. Here, we study Stylophora pistillata, a common branching coral in the Gulf of Eilat that harbors obligatory crabs from the family Trapezia. Two in situ surveys elucidated diel dynamics in compartmental distributions of Trapezia species within S. pistillata canopies compartments, associated with the crab’s body size and day/night activities. Whereas all crabs were found within sheltered spaces in the coral canopy understory or in the base during day hours, laboratory experiments revealed that nighttime distributions of small and large crabs (in middle and up compartments, respectively) are not intraspecific competition-borne, but rather, the outcome of preferred crab-size location for a novel feeding type, predation on demersal plankton. This study, thus, disclosed the importance of studying the coral’s three-dimensional structures and within canopies’ compartments for understanding the biology of dwelling species in the animal forests’ canopies.

Investigating the potential of escape openings and reduced mesh size to optimize snow crab (Chionoecetes opilio) pot catches in the Barents Sea

In the Barents Sea Norwegian pot fishery for snow crab (Chionoecetes opilio), fishing effort regulations and bait expenses create incentives to improve the catch rates. The fishery also currently captures a large proportion of sub-legal sized crab which must be sorted out and released. In this study, we used comparative fishing trials to determine the size dependent capture efficiency of three modified pot types designed to address these issues. A pot constructed with 40 mm mesh caught ∼35% more (CPUE, number of individuals per soak time) large crab (≥ 100 mm carapace width [CW]) than the pot typically used in the commercial fishery (140 mm mesh). However, it also retained massive amounts of small individuals (< 100 mm CW). The addition of four stadium shaped escape openings into the 40 mm and 140 mm mesh designs resulted in large reductions in catches of small crab, but also a ∼30% reduction in large crab. Analysis of size dependent catch comparison rates and selectivity parameters supported the CPUE findings. Of the tested designs, catches were best optimized by the currently used commercial pot. However, we conclude that a small mesh pot with escape openings has the potential to increase catches of large crab and reduce catches of non-commercial small crab. Further development of this design, particularly in terms of the dimensions of the escape openings, is therefore required.

Would Antarctic Marine Benthos Survive Alien Species Invasions? What Chemical Ecology May Tell Us

Many Antarctic marine benthic macroinvertebrates are chemically protected against predation by marine natural products of different types. Antarctic potential predators mostly include sea stars (macropredators) and amphipod crustaceans (micropredators) living in the same areas (sympatric). Recently, alien species (allopatric) have been reported to reach the Antarctic coasts, while deep-water crabs are suggested to be more often present in shallower waters. We decided to investigate the effect of the chemical defenses of 29 representative Antarctic marine benthic macroinvertebrates from seven different phyla against predation by using non-native allopatric generalist predators as a proxy for potential alien species. The Antarctic species tested included 14 Porifera, two Cnidaria, two Annelida, one Nemertea, two Bryozooa, three Echinodermata, and five Chordata (Tunicata). Most of these Antarctic marine benthic macroinvertebrates were chemically protected against an allopatric generalist amphipod but not against an allopatric generalist crab from temperate waters. Therefore, both a possible recolonization of large crabs from deep waters or an invasion of non-native generalist crab species could potentially alter the fundamental nature of these communities forever since chemical defenses would not be effective against them. This, together with the increasing temperatures that elevate the probability of alien species surviving, is a huge threat to Antarctic marine benthos.

Ocean temperature and density dependence as key drivers of the population dynamics of an intertidal crab at the Brazilian oceanic islands

AbstractUnderstanding how climatic and density‐dependent processes affect demography is crucial for predicting population responses to climate change. For marine invertebrates with complex life cycle such as decapod crustaceans, increasing temperatures might affect survival and development of early pelagic stages, whereas high density can increase competition and thus reduce growth and fecundity of older life stages. In this study, we investigate the effects of warm ocean events, body size and density on the population dynamics of the intertidal Sally lightfoot crab (Grapsus grapsus) at the Brazilian oceanic islands. Firstly, we assessed the trends of marine heatwaves (MHW) and positive temperature anomalies (ΔSST+) at the equatorial St Peter and St Paul (SPSP) Archipelago and Rocas Atoll and the subtropical Trindade Island. We then jointly analyzed short‐term count, capture‐recapture and fecundity data, and long‐term population monitoring data (2003–2019) using an integrated population model. Warm ocean events have become more frequent and intense only at the equatorial islands. Increasing MHW frequency positively influenced recruitment in the high‐density SPSP population, while MHW intensity and ΔSST+ frequency had negative impacts. Conversely, no climatic effects were observed for the low‐density Rocas population, which has the largest crabs. Despite a lack of warming in Trindade, this subtropical population with intermediate density and body size was negatively affected by ΔSST+. Our findings revealed population‐specific responses to climate change when accounting for local life history and ecology. Thus, environmental and density‐dependent effects should be broadly considered in future conservation studies regarding ocean warming impacts on marine invertebrate populations.

Development of an industry-funded fishery-independent survey and associated indices for managing a deep sea crab resource in Western Australia

The inclusion of fishery-independent data in stock assessments has been shown to have positive stock and financial outcomes for fisheries. A co-management approach between the government and commercial fishers in this limited-entry fishery led to the successful implementation of industry-funded, fishery-independent surveys of crystal crab, a deep water Geryonid crab, in two areas off Western Australia.While the instigation of these surveys was driven by a need for improved abundance indices for stock assessment, they have also provided an opportunity to better understand stock dynamics and composition. Structuring the surveys across the depth distribution (400–700 m) of crystal crabs demonstrated an apparent lack of depth-related size stratification in crystal crabs with large crabs captured throughout the species depth distribution. Female crabs, which mature below the legal minimum size for harvest, were a minor component of the catch and were more prevalent at the shallower end of their depth distribution. There also appeared to be a movement of pre-molt crabs to the periphery of their distribution (shallow and deep), in preparation to molt.There was a slight decline in the fishery-independent abundance (FIA) index from 2017 to 2019 mirroring the pattern displayed by the current standardized commercial catch rate, with an increase during the most recent survey (2020). The FIA index will be incorporated as an additional data source for the weight of evidence and size-structured integrated model for the assessment of the crystal crab resource off the west coast of Western Australia.The surveys, which were funded by industry and supported by government research staff onboard, have proved cost-effective, robust and sustainable, and a preferable means by which fishery-independent data could be collected for this commercially important Geryonid crab. The cost of the survey was partially offset by the retention of the legal catch. Such a collaborative model could be applied in fisheries world-wide to address the inherent biases of commercially-derived indices and the ever-increasing financial constraints on regulators to conduct stock assessments.

Short-term effects of hurricane events on the bioindicator species Ocypode quadrata inhabiting an island in essence free of anthropogenic disturbances

The effects of high-energy weather events may be most dramatic on coast dominated by sandy beaches, characteristic habitat of the Atlantic ghost crab. This study evaluates the impact of two hurricanes over Ocypode quadrata populations based on the hypothesis that natural disturbances may bring on a decrease in crab burrow size (population structure) and/or a significant decline in the burrow density (relative abundance). Densities of crabs, estimated via burrow counts and their size, evaluated according to burrow opening diameter, were quantified at six sites around Isla de Aves, before (July) and after (November) two major hurricanes (Irma and Maria) that hit the coastal areas on islands of the Caribbean Sea in 2017. Six 2 × 2 m areas were sampled at each site. The results reveal an effect on the size structure, while the population density did not present any evident change between the pre and post-hurricane moments. The decrease in the diameter of the burrows after the passage of the hurricanes, suggests that the larger crabs could have been removed during this event followed by an arrival of new recruits into the ghost crab population. The results suggest a short-term resilience to the impact of extreme climatic events in terms of population density, a scenario that could had been favored by several conditions. Isla de Aves has sandy beaches exposed to ocean currents, which favor the transport of larvae and the recruitment of juveniles. The availability and quality of food, due to its characteristics of being a main nesting site for sea turtles (mainly green turtle); therefore, it offers various resources in abundance (e.g., turtle eggs). As well as the characteristic of being an island practically free of anthropogenic disturbances.

Infestation by Octolasmis species (Lepadiformes, Poecilasmatidae) of the marine crab Lupocycloporus gracilimanus (Decapoda, Portunidae) from India

Abstract The portunid crab Lupocycloporus gracilimanus from Digha, Bay of Bengal, India was investigated for an infestation by the lepadomorph cirriped Octolasmis spp. About 93% of the epibionts examined were found attached to the surface of the carapace, abdomen and legs, and these were identified as Octolasmis warwicki (EOW). Only 7% of the epibionts were attached to the branchial lamellae, and these were identified as Octolasmis angulata (EOA). Twenty-seven O. warwicki were also found to have conspecific dwarf males (CDM) attached to the scutum: probably an adaptive strategy to maximize the total insemination. Both the epibionts and the CDM showed spatial preference for the posterior mesobranchial region of the carapace. Most of the CDM (27%) were seen as a single attachment on the epibiont. The distance between the epibiont and its nearest neighbour (DNN) was found to be strongly and negatively correlated (, ) with the number of epibionts, indicating its preference to stay in an intermediate-sized group rather than remain solitary, which probably would have facilitated the evolution of dwarf males (CDMs). A higher percentage of epibionts were observed to have attached CDMs when the DNN increased, and above the 25 mm DNN, all epibionts were having CDM attachments, which is believed to be a strategy to maximize the fertilization success of CDMs by reducing sperm competition. A strong, positive correlation (, ) was observed between the carapace width of the host crab and the numbers of the infesting epibionts, proving that the larger crabs are more susceptible to the infestation compared to the smaller ones. The sex ratio of the host crab was 1 : 5.5 (Male : Female), nevertheless, only the females were infested by the epibionts. The percentage of the prevalence, relative abundance and mean intensity of EOW infestation were recorded as 46.15%, 182.05% and 394.44%, respectively. None of the crabs had serious external or internal infestations that seemed to hinder the activities of the animal. This is the first report of the infestation of these Octolasmis species on the portunid crab Lupocycloporus gracilimanus from India.

The ghost of the past anthropogenic impact: Reef-decapods as bioindicators of threatened marine ecosystems

This study demonstrated the plasticity of reef-decapod according with the exposed anthropogenic pressure. Comparing the reef-decapods at sites with different anthropogenic pressures in two different ecoregions (tropical and subtropical reef ecotypes), we demonstrated that historical anthropogenic activity is molding directly and indirectly their population. A direct impact over target decapods for fishing (e.g. Lobsters and large crabs) that are removed directly by human activities. A positive indirect impact related to a top-down trophic imbalance with the increase of naturally dominant preys (small decapod) due to the removal of top predators. Thus, insufficient predators to control the abundant prey in a classic unbalanced prey-predator relationship. An indirect and negative impact, related to a bottom-up trophic imbalance, is the exclusion of niche-restricted species in association with benthic cover (e.g. corals). This also has the positive outcome, however, of increasing numbers of herbivores, detritivores and scavengers. As hypothesis, we propose that a current biodiversity balance in anthropogenically impacted ecosystem is just reflecting past trophic cascade events. Where the remaining biodiversity is monopolizing the vacant niches after the removal of components in a trophic chain. Therefore, we are suggesting that reef-decapod biodiversity, observed using visual identification, can be used to highlight the “Ghost of the past anthropogenic impact” in threatened ecosystems.

Comparative study of female Chinese mitten crabs based on their sizes and weights.

The Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species in China. While the price of a large crab will generally be 2-5 times higher than that of smaller crabs, it remains unknown whether nutritional quality is affected by market price. To investigate the effect of size on nutritional composition, adult female crabs were collected and assigned to grades I-IV according to decreasing size. The results showed that meat yield and conditional factors were significantly (P < 0.05) reduced with the decreasing size. The different sizes did not significantly (P > 0.05) affect levels of moisture, crude protein (except for hepatopancreatic crude protein), and total lipid. Grade III crabs had the largest hepatopancreatic crude protein level, which was significantly (P < 0.05) increased compared with grade I crabs. A balanced amino acid composition was found in grade IV crabs, while crabs from grades II and IV had the highest essential amino acids score. Levels of highly unsaturated fatty acids, including C22:6n3, and the ratios of n-3 polyunsaturated fatty acids (PUFA)/n-6 PUFA and C22:6n3 (DHA)/C20:5n3 (EPA) in the hepatopancreas were significantly (P < 0.05) increased in grade III crabs compared with the other grades. In conclusion, among the four grades smaller female crabs (average weight: 93-112g, grades III-IV) displayed an optimal nutritional quality.

Aretopsis sandybrucei, a new deep-water shrimp (Malacostraca: Decapoda: Caridea: Alpheidae) from the Coral Sea

A new alpheid shrimp, Aretopsis sandybrucei sp. nov., is described on the basis of three specimens collected from three deep-water banks in the Chesterfield Plateau of the Coral Sea, between New Caledonia and Queensland, Australia, at a depth range of 280–550 m. The new species is the first known deep-water species of the genus Aretopsis De Man, 1910, with its two congeners, A. amabilis De Man, 1910 and A. manazuruensis Suzuki, 1971, being confined to the lower intertidal and shallow subtidal areas, to a maximum depth of 50 m. Based on morphological grounds, A. sandybrucei sp. nov. can be easily separated from A. amabilis and A. manazuruensis by the generally much stouter third to fifth pereiopods, with their dactyli each bearing a very small secondary unguis on the flexor margin, in comparison to a much stronger one in the other two species. Aretopsis sandybrucei sp. nov. also differs from A. amabilis and A. manazuruensis by the less contrasting colour pattern, including the more translucent, dull yellowish chelae and tail fan. An association of A. sandybrucei sp. nov. with a deep-water hermit crab appears to be highly likely due to the presence of several large hermit crabs (Paguridae) in at least one of the three dredge/bottom trawl hauls, which was also containing a paratype of the new species. The taxonomic status of A. amabilis and A. manazuruensis is discussed.

Potential use of the Caribbean spider crab Maguimithrax spinosissimus for biofouling removal on marine aquaculture cages

Biofouling is a significant issue on marine aquaculture pens and is conservatively estimated to contribute to 15% of production costs. With a global increase in the demand for sustainable aquaculture products a search for sustainable non-toxic alternatives to chemical treatment and manual removal of biofouling organisms, such as biological control, are becoming more sought after. In the laboratory experiments Caribbean spider crabs (Maguimithrax spinosissimus) exhibited nocturnal patterns of activity. They consumed between 3.3 and 4.16% bodyweight (BW) of algae in 22–24 °C water, and between 5.61 and 8.55% BW in 26–28 °C water. Although this species is primarily herbivorous they also readily consumed whole fish (Lutjanus apodus). The spider crabs were placed on a heavily fouled, unoccupied SeaStation 3000 cage offshore of Eleuthera, The Bahamas, to determine their ability to remove fouling organisms. Large crabs (382 g – 1344 g) confined in mesh cages on the outside of the pen effectively removed between 40% (after two weeks), and 90% (after four weeks) of fouling organisms. Crabs were more effective at removing growth than manual scrubbing by a diver. Grazing by the crabs was non-discriminatory, with no significant change in the proportional makeup of epibionts at the end of the trial. The survival rates of crabs inside the cage varied between 50% and 55% when not including escapees, and between 66% and 94% when including escapees during 3 to 6 month trials, with no significant decline in health status (blood protein levels). The Caribbean spider crab is a good candidate both economically and environmentally for controlling biofouling on aquaculture cages, could be used in multi-trophic aquaculture systems, and marketed as an environmentally friendly seafood.

Comparison of the growth performance and nutritional qualities of Chinese mitten crab (Eriocheir sinensis) with different stocking densities in rice-crab culture systems

This study investigated the comparison of the growth performance and nutritional qualities of Chinese mitten crab (Eriocheir sinensis) with different stocking densities (D02: 0.2 inds/m2; D03: 0.3 inds/m2; D04: 0.4 inds/m2; D05: 0.5 inds/m2; D06: 0.6 inds/m2) in rice-crab culture systems. The result showed the D04 group crabs had higher gonadsomatic index (GSI), meat yield (MY), total edible yield (TEY), crude lipid levels of hepatopancreas and the crude protein levels of gonads than those of other groups crabs. The muscle and gonads of D04 group crabs had better essential amino acid (EAA) levels. The levels of polyunsaturated fatty acids (PUFA) in the hepatopancreas and gonads were significantly increased in the D04 group crabs compared with other groups crabs. The stocking density of D04 group has a more obvious promotion effect on the relative expression of molting and growth related genes compared with other groups. Taken together, it can generally be concluded that the male crabs raised by 0.4 inds/m2 have the highest nutritional quality even though they are not the largest crabs.

Size selectivity and optimal soaking time of hoops and traps targeting the blue swimming crab &lt;i&gt;Callinectes arcuatus&lt;/i&gt; in Cuyutlan Lagoon, Mexico

The selectivity of two types of commercial fishing gear (crab hoop/traditional gear and rigid rectangular cage traps) targeting blue crabs (Callinectes arcuatus) in Cuyutlan Lagoon, Mexico, was assessed. The effect of soak time on crab catches versus the retention and escape rate of organisms was also evaluated. Results suggested that traps captured larger individuals than hoops. The carapace width of crabs was significantly different between the fishing gears used: 63.9% of crabs caught with hoops were &lt; 95 mm (sizes ranged from 40 to 113 mm) and 40.7% of crabs caught with traps were &lt; 95 mm (range: 49 to 120 mm). Results also showed that catch rates were high during the first two hours and decreased after the third hour. The crabs tended to escape after several hours of soak time. The study found that the traps captured larger crabs than the hoops, suggesting that traps are a suitable fishing gear for catching blue swimming crabs in Cuyutlan Lagoon.