Eroded Swimmeret Syndrome: Update of the Current Knowledge

Eroded swimmeret syndrome (ESS) was first described in 2014 from Swedish signal crayfish (Pacifastacus leniusculus (Dana)), and later also from Finland, with gross symptoms and disease agent candidates identified and described by 2015. The ESS was first discovered affecting alien signal crayfish in Fennoscandia. The ESS is caused by a multiple infection involving Aphanomyces astaci (Schikora) and Fusarium species complex (SC). The ESS symptoms include first melanised spots in swimmerets, then partial swimmeret erosion and finally loss of a swimmeret. There could be a total loss of all swimmerets in the most severe cases. Both females and males can be affected by the ESS. In females, the ESS lowers reproductive success while in males the ESS often causes erosion of the gonopods and thus possible partial failure in mating. The ESS is more frequent among mature females that have reproduced once compared to immature females or those that are mature but have not yet reproduced. The proportion of females with ESS has ranged from 10 to 50% among Lake Saimaa signal crayfish in Finland and in a wider survey from Sweden the range was from 0 to 38%. Among Lake Saimaa male signal crayfish, the ESS proportion has been less than 10%, while it was only 0.6% in the Swedish data. The ESS has also been observed among alien signal crayfish in Switzerland. There are recent observations of ESS affecting narrow-clawed crayfish, Pontastacus leptodactylus (Eschscholtz), in Croatia and Romania (i.e., among native European crayfish stocks). Here, we summarise current knowledge about the ESS and speculate on a few potentially crucial impacts of this syndrome.

Epigean Crayfish of the Potomac River Basin in West Virginia: Zoogeography, Natural History and Conservation

Crayfish are an aquatic fauna of conservation concern, yet regional studies are lacking on zoogeography and life history. We compared recent and historical species distribution data and assessed conservation standings of native and nonindigenous crayfish of the Potomac River Basin in West Virginia. From 2007–2011, a total of 1764 crayfish were collected from 159 sites. Data collection included species abundance, morphometrics, and life history parameters. Percentages of the number of individuals of each species of the total catch were 36.3% (Cambarus bartonii), 34.6% (Faxonius obscurus), 23.4% (Faxonius virilis), 3.6% (Procambarus cf. zonangulus) and 2.0% (Cambarus carinirostris). Cambarus bartonii was present throughout the drainage, F. obscurus was collected primarily from the North Branch, South Branch, and Cacapon river watersheds, and C. carinirostris was only collected in the South Branch watershed. Two nonnative species, F. virilis and P. cf. zonangulus, were only present in tributaries downstream of the Cacapon River watershed. Spinycheek crayfish (Faxonius limosus) were not collected during our survey, which suggests its possible extirpation from the West Virginia portion of its range. Our zoogeographic and life history data could serve as a baseline for future conservation-oriented monitoring efforts of the Potomac River watershed.

Is Native Crayfish Conservation a Priority for United States and Canadian Fish and Wildlife Agencies?

Crayfish are key organisms in freshwater ecosystems across the United States (USA) and Canada, yet are among their most highly imperiled taxonomic groups. In 1996, a committee of prominent USA crayfish biologists warned of a crayfish imperilment plight and neglect of the fauna by natural resources agencies. It is unclear whether crayfish conservation has been prioritized by those agencies in the intervening decades. Our objective was to evaluate the status of crayfish conservation and management in 50 USA and 13 Canadian fish and wildlife agencies through a telephone survey. Fifty-one percent of agencies employed biologists to conduct crayfish work, mostly in the southern USA, and focused on threats (e.g., invasive species) or species’ distributions and conservation status. Of the 32 agencies working on crayfish, 59% considered them a priority, but 53% acknowledged insufficient funding. The most commonly cited information needs were threats, species compositions (native and introduced), distributions, conservation status assessments, and ecology. We report an encouraging but limited increase in agencies working on crayfish over the past two decades.

Determining Suitable Thermal Regimes for Early Instar Redclaw Juveniles, Cherax quadricarinatus (von Martens, 1868) (Decapoda, Parastacidae), for a Proposed Nursery Phase

Modern, intensified aquaculture typically involves three production phases; hatchery, nursery, and grow-out. For redclaw crayfish aquaculture however, such delineation has been ill-defined. Farming of redclaw was initiated based on the putative beneficial physical and biological attributes of the species, which suggested production methods would be relatively simple. The simple approach proved to be inefficient and only partially effective, which hindered industry development. Hatchery technology now exists to supply seed stock for grow-out, but hatchery production is variable, and the performance of hatchery reared juveniles is inconsistent. A nursery phase has been proposed between hatchery production and grow-out of approximately 3 weeks duration, sufficient to allow 2 or more moults. An important primary parameter in the proposed nursery phase is the thermal regime that will support optimum survival and growth. This study quantified the effect of temperature on the growth and survival of redclaw juveniles for a 22-day nursery phase. Temperature had a statistically significant effect on the survival of juveniles, whereby, the high temperatures were associated with high mortality, and the lower temperature treatments were associated with very low mortality. Survival was 98 to 100% for craylings held at temperatures between 18°C and 22°C, and between 0% and 6% for craylings at temperature treatments of 25°C to 32°C. Mortalities within treatments between 25°C and 30°C, primarily occurred from day six to day eleven, corresponding with the initiation of moulting. Change of mass of crayfish was significantly higher with increasing temperature between 18°C and 22°C and at individual weights that suggest they had completed a moult. This study suggests a water temperature of 22°C is optimal for survival and growth in a nursery phase.

Morphology and Weight-length Relationships for the First Six Instars of Cherax quadricarinatus (von Martens, 1868)

Cherax quadricarinatus (redclaw) aquaculture has not achieved the industry growth that had been predicted in the early days of development. Provision of quality juvenile crayfish seed stock has been identified as a critical factor in overcoming industry development inertia. Hatchery technology has been developed to produce independent craylings and a nursery phase is now being developed to nurture the delicate craylings to a more advanced and robust juvenile stage, suitable for pond stocking. As part of the nursery development, clear definitions of the successive stages from egg through the first several instars, are required. Although some morphological descriptions of the early stages of redclaw have been made, the characteristics and nomenclature for stages from egg through to an advanced juvenile need clarification. A naming system is proposed (Egg, L1, L2, J1, J2 and J3) for the first six instars from egg, based on gross morphology and allometric relationships. Egg volume, wet weight and ocular carapace length (OCL) were analysed through linear regression. Based on these variables, the size of each instar is defined. Descriptions and photographs of the six instars provide a visual reference for identification. Five of the six instars had a significant relationship between wet weight and OCL. Both significantly increased for each successive instar. Lyophilized (dry) weight was not significantly different between stages until after instar J1, where endogenous feeding begins. The growth of the first four instars, in terms of wet weight and OCL but not dry weight, suggests an extra endogenous source of nutrition in addition to the yolk supply. Branchial water uptake during ecdysis has been proposed as a route for dissolved organic matter or small particulate matter to be acquired by the crayfish during the lecithotrophic, nonexogenous feeding stages, as an additional food source that might further enhance growth and survival.

Description of the First Juvenile Stage of Cambaroides dauricus and the Second Juvenile Stage of Pacifastacus connectens

Morphology of the first juvenile stage of Cambaroides dauricus (Cambaroididae) and the second juvenile stage of Pacifastacus connectens (Astacidae) are described and illustrated. Morphological features of body regions, setae, and number of articles of appendages are compared with that of other species of Cambaroididae and Astacidae, respectively. For each taxon, the characteristics of the juvenile body and appendages are similar to their respective family members. The relationships between European Astacidae are examined in light of the findings.

Evaluation of Four Practical Diets on the Growth and Survival of Juvenile Redclaw, Cherax quadricarinatus (von Martens, 1868)

Redclaw, Cherax quadricariatus (von Martens) has shown promise as an aquaculture species but commercial development has been constrained by variability of production, perhaps due to poor survival and growth of early craylings. Diet contributes to survival and growth and previous studies have determined requirements for larger redclaw, but little research exists for the early craylings. An experiment was performed to evaluate survival and growth of early instar redclaw using four diets; Frippak (commercial shrimp diet), CSIRO compound diet, bloodworms, and on-grown Artemia. Bloodworms and Artemia produced significantly higher survival of craylings over two weeks than the two other diets. Artemia diet had a significantly higher weight increase than bloodworms or the CSIRO diet, but not Frippak, which did not differ from bloodworms or CSIRO. Biomass was significantly higher when fed Artemia. High mortality in the Frippak and CSIRO diet treatments were not wholly attributable to nutritional deficiencies as the manufactured diets became less physically accessible, potentially reducing intake, leading to difficulties completing ecdysis and eventually death. This study concluded that Artemia and bloodworms promoted highest survival, and Artemia and Frippak the highest weight gain. The best combination of survival, weight gain and biomass was with the Artemia diet.

The annual flood pulse mediates crayfish as a major diet constituent of carnivorous fishes in south Louisiana

Anthropogenic modifications to river-floodplain systems can decouple floodplains from mainstem inputs, alter flood pulse dynamics, and disrupt population dynamics and trophic web stability of aquatic biota. The Atchafalaya River Basin (ARB) receives an annual flood pulse from the Mississippi River that contributes to high crayfish abundance. Conversely, reduced crayfish abundance in the Barataria Basin (BB) is attributed to the system no longer receiving an annual flood pulse from the Mississippi River. Therefore, the purpose of this research was to determine if the absence of an annual flood pulse and reduced crayfish abundance influenced the diets of carnivorous fishes by examining stomach contents of fishes from both basins. Stomach contents were grouped as crayfish, fish, non-crayfish invertebrate, and herpetological. Although the percent occurrence of crayfish in fish stomachs differed between floodplain inundation and low-water periods in the ARB, crayfish were still the major diet constituent of ARB fishes during both periods. Non-crayfish invertebrate was the major diet constituent in BB fishes, with crayfish ranking as the second fewest diet constituent present. Our results demonstrate how flood pulse dynamics influence crayfish, and ultimately trophic webs, in large river-floodplain systems.

A review of juvenile redclaw crayfish Cherax quadricarinatus (von Martens, 1898) aquaculture: global production practices and innovation

The Australian Redclaw crayfish, Cherax quadricarinatus, has been the subject of aquaculture development for more than 3 decades. Farm production from Australia and from around the world for this species has been relatively low, as suitable production technology continues to develop. The production of redclaw juveniles for the purpose of stocking to ponds for on-growing to marketable size, has been a particular constraint and new approaches to breeding and mass production of craylings have provided renewed impetus to industry expansion. This paper reviews the literature concerning redclaw juvenile production and provides a status report of current practices and innovations that may support further expansion of redclaw aquaculture.

Relaxed attitude towards spreading of alien crayfish species affects protection of native crayfish species: case studies and lessons learnt from a Fennoscandian viewpoint

The spreading of the alien signal crayfish (Pacifastacus leniusculus) is posing an ongoing threat to native European crayfish species in Fennoscandia, like the native noble crayfish (Astacus astacus). The signal crayfish is commonly a chronic carrier of the crayfish plague (Aphanomyces astaci), thus, in addition to being more competitive than noble crayfish, it also has a competitive advantage in this disease over the noble crayfish. The challenges rising from the introduction of the alien signal crayfish to Sweden, Finland and finally also Norway, are similar in nature. The licensed and unlicensed spreading of this species also has a similar history in these countries. In this paper we describe some of the patters of the spread of alien signal crayfish and highlight the detrimental nature of an alien crayfish, accompanied by a highly virulent disease, to native Fennoscandian crayfish and also to native Fennoscandian ecosystems. A halt to the further spreading of alien signal crayfish in Fennoscandia is the only means to ensure successful conservation outcomes for the noble crayfish.