Predation on invasive redclaw crayfish Cherax quadricarinatus by native fishes in the Kafue River,Zambia

The stomach contents of eight species of predatory or omnivorous fish caught in gillnets in the Kafue River in May and June 2010 were examined to determine the relative importance, expressed as ‘prominence value’ (PV), of crayfish Cherax quadricarinatus in their diet. Four species, Clarias gariepinus, Schilbe intermedius, Serranochromis robustus and Serranochromis angusticeps, had fed on C. quadricarinatus. The PV of C. quadricarinatus was highest in C. gariepinus, in which the quantity and size of crayfish eaten was significantly correlated with standard length (SL) of fish >200 mm SL. Predated C. quadricarinatus were significantly smaller (mean carapace length [CL] 30 mm; SE 1.2) than those caught in gillnets (mean CL 76 mm; SE 0.9). No C. quadricarinatus remains were found in the stomachs of Oreochromis andersonii, Synodontis macrostigma, Serranochromis macrocephalus or Mormyrus lacerda.     

Aspects of the biology of the big-handed crab,Heterozius rotundifrons (Decapoda: Brachyura), from Kaikoura,New Zealand

Abstract

From January 1975 to June 1976, samples of Heterozius rotundifrons A. Milne Edwards, 1867 were taken monthly from the intertidal zone at First Bay, Kaikoura Peninsula (42°25′S, 173°42′E). Small crabs (< 8 mm carapace width) were never common; they were either too cryptic to be collected in quantity, or have a different habitat from larger crabs. Ovigerous females were present in all months except February (in both 1975 and 1976), but generally formed less than 50% of the total sample of females each month. The number of newly deposited eggs (0.75×0.81 mm) carried by females increased with increase in carapace width according to the equation y = -1123.56+102.97x (r ² = 0.8213). Egg development lasted 3–5 months, and egg mortality during this period was almost 10%. The overall sex ratio for the 18-month sampling period was 1846 ♀ : 993 ♂, which suggests that females were approximately twice as numerous as males. However, when crabs were sorted into size classes it was evident that the sex ratio was not significantly different from 1:1 in crabs of 6–12 mm carapace width, whereas females significantly (P<0.001) outnumbered males in the 13–21 mm size range. The right and left chela were approximately equal in length in females of all sizes, but the right chela of large males was greatly enlarged compared with the left, and with the chelae of females of comparable carapace width. Increase in the growth rate of the males’ right chela commenced at a carapace width of approximately 11.0 mm. Since the smallest ovigerous female collected also had a carapace width of 11.0 mm, it is concluded that both males and females attain sexual maturity at this size.     

Nest defense and aggressive interactions between a small benthic fish (the johnny darter Etheostoma nigrum) and crayfish

Synopsis Aggression by nest-guarding male johnny darters, Etheostoma nigrum, against intruding crayfish was investigated in laboratoy experiments and field observations. In the laboratory, darter success in chasing crayfish, Orconectes rusticus, from the nest site was inversely related to crayfish size. Small crayfish (less than 15 mm carapace length) were routinely evicted from the nest area by nips directed at the posterior end of the abdomen. Although such aggressive behavior was less successful against larger crayfish, even the largest crayfish tested (carapace length 30–32 mm) were chased from the nest area in 33% of the trials. Those large crayfish that entered nests often remained despite repeated attacks by the male johnny darter and egg predation was observed. In a small Ohio stream, openings to johnny darter nests were generally between 7 and 13 mm. Thus crayfish with a carapace height greater than 13 mm (corresponding to a carapace length greater than 29 mm) would not be able to enter johnny darter nests. In field observations, male Johnny darters successfully defended nests against another crayfish species (Orconectes sanborni, carapace length 12–29 mm). Together, aggressive behavior and small size of nest entrances allow the johnny darter to successfully reproduce in areas with abundant crayfish. The Unit is sponsored jointly by the United States Fish and Wildlife Service, The Ohio Department of NaturalResources, and The Ohio State University.     

Notes on the biology of Cancer bellianus (Brachyura, Cancridae) around the Canary Islands

Information on biometric and biological parameters of Cancer bellianus Johnson, 1861 (Crustacea, Decapoda, Brachyura, Cancridae) off the Canary Islands is given. Crabs examined were collected during experimental fishing surveys during 1974–1998. Carapace length, carapace width, total wet weight, sex and ovigerous condition were determined. This species was caught at depths from 153 to 750 m, the deepest ever recorded. Size frequency distributions were assembled and size-weight relationships were estimated by sex. Sex-ratio as a function of size and depth was determined. The size at first maturity was calculated by analysing the relative growth between the carapace length and the left chela width: 103.5 mm CL in males, 101.2 mm CL in females. Ovigerous females, egg size and fecundity estimates are reported apparently for the first time.     

Sexual dimorphism of the European Pond Turtle,Emys orbicularis (Linnaeus, 1758), in Anzali Lagoon,Iran (Reptilia: Emydidae)

The morphometric characteristics of the European Pond Turtle, Emys orbicularis, were studied at Anzali lagoon on the southern coast of the Caspian Sea. Males were on average (N=249) with 272.0?g significantly lighter than females with 447.0?g, and average carapace length was significantly smaller (123.0?mm in males, 139.0 in females). Females exceeded males also in all other studied characters (carapace width, plastron length, plastron width, and scute height). The sex ratio of male to female was 1 to 1.03, and the comparison of total tail length and cloaca-tail tip length revealed a difference between the position of the cloaca in both sexes, a character useful for sex determination in this species.     

Haemolymph characteristics of a copper-tolerant decapod Orconectes virilis (Hagen) (Astacidae, Crustacea)

The mean haemolymph volume in a copper-tolerant, intermoult (C2-C4) adult (more than a year old) Orconectes virilis, as determined by [14C-carboxylic] inulin dilution method, ranged from 61.17 microliters in females (mean wet body weight = 4.34 g; mean carapace length = 4.43 cm) to 61.79 microliters in males (mean wet weight = 5.73 g; mean carapace length = 4.49 cm). The mean haemolymph volume per cent varied from 14.5 (in females) to 31.1 (in males). Haemolymph from males had an average pH of 7.35, osmotic pressure of 414.1 mmol/kg H2O, and a specific gravity of 1.0603, while that from females averaged a pH of 7.48, osmotic pressure of 433.6 mmol/kg H2O and a specific gravity of 1.0469. Mean total haemocyte counts ranged from 3,434/mm3 (1,000/mm3 halinocytes, 1,125/mm3 hemi-granulocytes and 1,309/mm3 granulocytes) in males to 4,905/mm3 (1,525/mm3 halinocytes. 1,490/mm3 hemi-granulocytes and 1,890/mm3 granulocytes) in females.     

Long-term studies on sex and size structures of the non-native crab Eriocheir sinensis from Polish coastal waters

The Chinese mitten crab Eriocheir sinensis is a non-native species that appeared in European waters more than 100 years ago. Size and sex structure as well as biological condition of populations of Eriocheir sinensis sampled annually between 1999–2014 from the eastern Baltic Sea coast (1999–2007 Gulf of Gdansk and 2008–2014 Vistula Lagoon, Poland) were analysed. Males were dominant over females, with a sex ratio of 1.6:1. Carapace width of all collected specimens (n?=?467) ranged from 33.3 to 89.1?mm and the mean values for specimens from Gulf of Gdansk and Vistula Lagoon were 62.4?±?8.1?mm (n?=?171) and 66.6?±?7.7?mm (n?=?296) respectively. There were no statistically significant differences in carapace width between males and females. It is important to note that there were no individuals with a carapace width less than 30?mm, which may indicate a lack of an established population of this species from the eastern Polish coast. The wet weight of all specimens ranged from 30.9 to 321.9?g and the mean values for all specimens from the Gulf of Gdansk and the Vistula Lagoon were 119.4?±?45.2?g (n?=?101) and 141.8?±?47.9?g (n?=?223), respectively. The wet weight of an individual was significantly correlated to carapace width and the exponent b reaching values close to 3 may indicate their good condition.     

Relative growth before and after sexual maturity in Ocypode platytarsis (Milne Edwards) and Ocypode cordimana (Desmarest) (Crustacea: Decapoda)

The relative growth of two species of the genus Ocypode inhabiting different ecological niches was studied before and after sexual maturity. The growth coefficient of both sexes of O. cordimana, which inhabits supra-littoral zones, is higher than that of O. platytarsis found in wave-wash zones.s

Some characteristics such as eyestalk length, major chela width and obdomen width do not show any difference in the growth pattern of either species of Ocypode at the onset of sexual maturity. Other characteristics such as minor and major chela length in male O. platytarsis; carapace length, minor chela length and width in female O. platytarsis; major chela length and third walking leg length in male O. cordimana showed a difference in the growth pattern after the onset of sexual maturity.

Major chela length of males of both species is clearly a sexually dimorphic feature since it showed an increase in the growth coefficient after sexual maturity. Merus length in male O. platytarsis and minor chela length in female O. cordimana also showed such sexual dimorphism.

There are several characteristics in which the growth coefficient declines after sexual maturity. The change in growth coefficient of different characteristics may depend on the adaptive value of the characteristic in reproductive or post-reproductive activities of O. cordimana and O. platytarsis.     

Ranging behaviour of a large freshwater invertebrate, the white-clawed crayfish Austropotamobius pallipes

• 1 Radio‐telemetry and mark‐recapture methods were used to study the summer movements of adult and juvenile white‐clawed crayfish, Austropotamobius pallipes from a wild population in a small braided stream, Dalton Beck, North Yorkshire, U.K. Radio‐transmitters were attached to the chelae of 18 large (> 35 mm carapace length) crayfish and individuals were subsequently located to within 0.15 m. Additionally a total of 888 crayfish were marked with carapace brands, and 83 were recaptured.
• 2 Radio‐tracked crayfish exhibited significantly greater local activity at dusk (21.00–00.00) than at dawn (03.00–06.00), or during morning (09.00–12.00) and afternoon (15.00–18.00) monitoring periods.
• 3 The greatest movements of radio‐tracked crayfish occurred within 2 days of release. After this time, periods of residence were interspersed by movements to new locations, interpreted as establishment of ephemeral home areas. It is suggested that the initial large movements were the result of a ‘fright response’ following capture.
• 4 Movements varied widely between individuals, some moving more than 300 m in 10 days, while others showed little movement over an equivalent time period. Mean (±SE) daily movements were 4.6 ± 3.0 m for males and 1.5 ± 1.0 m for females. Although crayfish often used specific home sites for in excess of 7 days, displaced animals did not return to home sites.
• 5 The total distances travelled and the mean distance travelled per day by individual radio‐tagged crayfish did not differ significantly between upstream or downstream directions or between males and females. This was also the case for marked crayfish used in mark‐recapture studies.
• 6 Positive correlations between distance moved per day and size (carapace length) were found for downstream movements by male and female crayfish, but not for upstream movements.
• 7 Some preliminary observations of the response of crayfish to flood events suggested that these could be catastrophic with two out of five tracked crayfish found dead after a high stream‐discharge event.

     

Reproductive performance in captivity of Austropotamobius pallipes in Abruzzi Region (central Italy)

Austropotamobius pallipes juveniles for restocking should originate from native breeders to preserve the genetic integrity of the populations. We compared the reproductive performance in captivity of A. pallipes populations of four drainage basins of the Abruzzi Region to assess their reproductive efficiency and improve their aquaculture. The broodstock were collected before the breeding season and reproduction took place in an experimental hatchery. The female carapace length ranged from 35.4 to 59.0?mm. Spawning occurred in 84% of females (range 69–93%) and the mean number of eggs per female was 89 (range 80–104). No significant differences were observed among the groups. Close to hatching, two groups maintained a high percentage of egg-bearing females (52%) and a high number of eggs, while the other groups lost most of their eggs. At the end of the cycle, the stage 2 juveniles obtained represented 19.5% of the initial egg number. The efficiency for stage 2 juvenile production ranged from 48.2 to 0.1%, and the mean number of stage 2 juveniles per female ranged from 42.2 to 1. These differences were not attributable to maternal size, but the characteristics of the brooks of origin might have influenced the reproductive performances of crayfish in the hatchery.     

Growth in the crayfish Austropotamobius pallipes (Crustacea: Astacidae)

SUMMARY. The growth of Austropotamobius pallipes was studied in the River Ouse during 1976–78. Growth of mature crayfish (>2.5 cm carapace length) was followed by determining the relationship between the growth increment at moult and premoult carapace length, together with the frequency of moulting of different categories of crayfish. These data are supplemented by the recapture of marked individuals and the measurement of crayfish held in corves in the river. Growth was limited to the period May–October when water temperatures exceeded 10°C. Growth rates of male and female crayfish are similar until maturity is reached, thereafter males moult twice per year and the majority of females moult once. No crayfish in excess of 3.7 cm carapace length has been observed to moult more than once per year. Growth of juveniles (<2.5 cm carapace length) was estimated from size frequency distributions constructed from regularly taken samples. Growth rates of juveniles showed great variation both between and within year classes. In the hot dry summer of 1976, juveniles exhibited faster growth rates (instantaneous growth rates (G) for 0+ and 1 + crayfish were 0.029 and 0.013 mg mg⁻¹ day⁻¹. respectively) than in other years. Laboratory experiments on the effect of temperature on the growth rate of 0 + crayfish were undertaken; for crayfish at 15°C. G = 0.0138 (0–53 days) and at 10°C, G = 0.0003 (0–90 days). Crayfish held at 10°C failed to undergo a single successful moult. At 20°C crayfish exhibited exponential growth over the first 40 days, with G = 0.0189. declining thereafter to G = 0.012 (40–90 days).     

Size,but not sex,predicts pinch force and exoskeleton mechanical properties in crayfish of the genus Faxonius

Studies of animal weaponry and defensive structures rarely take into consideration their underlying mechanical properties. We measured the compressive strength and thickness of the exoskeleton of the claw (chela) in two North American crayfish species, Faxonius virilis and F. limosus. We performed similar measures on the carapace, a body region not directly involved in agonistic contests. Males of both species generated significantly stronger maximum pinch forces than females. However, these differences can be attributed to differences in claw size between the sexes. The thickness (ultrastructure) of the claw exoskeleton was a significant predictor of its compressive strength and likely explained the difference in compressive strength we observed between the two species. Neither claw thickness nor claw compressive strength was correlated with maximum pinch force. Additionally, we found that crayfish body size was a strong predictor of carapace compressive strength and thickness, whereas sex was not. The claw had greater compressive strength and thickness than the corresponding values for the carapace. Our study shows that the mechanical properties of the crayfish exoskeleton are largely a function of size and highlights the need to integrate mechanical properties into studies of animal morphology and performance.     

Chaerilus pseudoconchiformus sp. n. and an updated key of the chaerilid scorpions from China (Scorpiones,Chaerilidae)

A new species, Chaerilus pseudoconchiformus sp. n., is described from Xizang, China. The present new species is distinguished from its congeners by a body length of 32−40 mm, carapace with the anterior margin straight, chela with length/width ratio average of 3.3 in males (3.2−3.4, two adults), and 2.5 in females (2.3−2.6, nine adults), eight or nine (eight usually) rows of denticles on fixed and movable fingers of pedipalp chelae, five pectinal teeth in males and three or four in females. To date, the chaerilid species fauna of China consists of nine species. An updated identification key to Chaerilus from China is presented.     

The artificial incubation of crayfish eggs: review and report from an experimental study concerning the effects of offspring origin (maternal or artificial incubation) on the survival and growth of juvenile signal crayfish (Pacifastacus leniusculus, Astacidae)

The development of artificial incubation techniques in astacid crayfish has attracted attention from scientists in many countries ever since the nineteenth century. It is only in the last few years that these techniques, along with studies on egg storage and transport, have provided reliable options for improving the reproductive phase in farming. The juveniles produced need to be reared until they reach a sufficient size both for restocking and for growing purposes. In view of the current level of knowledge of rearing juvenile astacids, two 80-day experiments were carried out under controlled conditions to compare the survival and growth of Stage 2 juvenile signal crayfish (Pacifastacus leniusculus) from two origins: maternal or artificial incubation. In the first experiment, three treatments were tested: juveniles from artificially incubated eggs with formaldehyde treatments, juveniles from maternal incubation and a mixture from both origins (50% each). Survival rates ranged from 87.8% to 93.3% with no significant differences among treatments. Crayfish from artificial incubation grew significantly faster (11.47 mm carapace length (CL), 373.80 mg weight) than crayfish from maternal incubation. In the second experiment, a bifactorial design included four treatments: the crayfish was derived from artificial or from maternal incubation and was fed once a day or twice a day. Final survival rates ranged from 68.89% to 77.78%, with no significant differences among treatments. Crayfish from artificial incubation grew significantly faster than crayfish from maternal incubation. The highest CL (14.54 mm) and weight (780.13 mg) were reached by the juveniles from artificial incubation that were fed once a day. No significant differences were found between the two feeding frequencies. Results showed that artificial incubation with formaldehyde treatments had no harmful effects and made it feasible to get a better performance from the juveniles obtained.     

Breeding biology of the Louisiana red swamp crayfish Procambarus clarkii Girard in Lake Naivasha,Kenya

This paper describes the breeding biology of the Louisiana red swamp crayfish (Procambarus clarkii Girard) that has been introduced in a tropical lake, Naivasha. Notable differences in crayfish biology are found between the place of origin in Louisiana and lake Naivasha.In Naivasha sexual maturity in females is reached at a larger size (42 mm carapace length (CL), 76 mm full length (FL)) than in males (40 mm CL, 71 mm FL). The corresponding figures for Chalmette area of Louisiana are 31–32 mm CL for both sexes and at Ben Hur Research Centre, Louisiana, 33 mm CL. The females weigh between 15 and 20 g at the onset of egg deposition. The corresponding Louisiana values are from 5 to 10 g. Crayfish in Naivasha as in Louisiana breed both inside burrows which are 10–70 cm deep, and on the sediment in shallow water at a depth of between 0.5 and 4 m. These observations suggest that reproduction is very much a lake edge activity. The number of breeding individuals in Naivasha varies with the trend of the water surface level. Sexually active females (form I) as judged from secondary sexual characters (appearance of basal hooks at the base of 3rd and 4th walking legs) persist throughout the year at no less than 60% of the adult male population. This is confirmed by the appearance of recently hatched juveniles (3.4 to 6.5 mm CL) in the water throughout the year. Similarly berried females in Naivasha are found throughout the year, though with peaks at irregular intervals. In Louisiana breeding takes place only from August through November with a single peak in October. The fecundity of crayfish in Naivasha is 433 (SE ± 21, N = 133) and there is a positive correlation between body length and egg number.     

Female reproductive pattern of Callinectes sapidus Rathbun, 1896 (Brachyura: Portunidae) in Iskenderun Bay,Eastern Mediterranean

We studied the female reproductive pattern of Callinectes sapidus, which was introduced to the Mediterranean in the 20^th century. We assessed female size at first maturity, fecundity, and fecundity relationship to size in Iskenderun Bay, eastern Mediterranean, Turkey. Samples were collected between July 2014 and June 2015 using bottom trawling at depths ranging from 1 to 50 m. A total of 322 crabs were caught of which 308 (95.7%) were females including 116 ovigerous ones. The minimum carapace width of the mature females was 39.1 mm and the mean carapace width 123.8 mm. The carapace width of ovigerous females varied between 95.1 and 144.5 mm, with a mean of 120.3 mm. The highest number of ovigerous females was observed in July and August. Mean fecundity was 1.91 million (667,950–4,669,853) eggs per female. A weak positive linear relationship between fecundity and carapace width was noted, as well as a high correlation with total egg weight. In the eastern Mediterranean, maturity sizes of females were smaller than those in the native region of the species.     

Size at sexual maturity,egg number and reproductive output of the snapping shrimp Alpheus euphrosyne euphrosyne De Man, 1897

Abstract

Aspects of the reproductive biology of snapping shrimp Alpheus euphrosyne euphrosyne inhabiting a tropical estuary were studied between August 2007 and July 2008 by examining 1309 females of 8.5–21.5 mm carapace length. Although the occurrence of ovigerous females was noted from October, the main breeding season extended from January to March. Size at 50% sexual maturity was estimated as 10.6±1.40 mm CL. Number of eggs per brood ranged from 141 to 1553 in females of 11.2 to 19.2 mm CL and mean absolute fecundity was estimated as 480±272 eggs. Regressions of log egg number on log total length, log carapace length and log weight revealed isometric relationships (p <0.01). Results of ANOVA revealed significant variation between mean short and long axes of eggs among five embryo developmental stages (P <0.05). The estimated egg batch 33 volume ranged from 4.99 to 32.09 mm³ with a mean of 12.44 mm³. Estimates of reproductive output from 41 females ranged between 8.21 to 31.25% with a mean value of 18.55±5.81.     

The potential use of PIT telemetry for identifying and tracking crayfish in their natural environment

A method for tracking crayfish and other benthic animals in rivers and streams, based on passive integrated transponder (PIT) technology, using a portable detector was investigated. The effect of implanting crayfish with PIT tags and the efficiency of the PIT tag detector system at locating tags is described. In a laboratory study 30 signal crayfish Pacifastacus leniusculus (>33.7 mm carapace length) were internally implanted with PIT tags (12-mm long×2.1-mm diameter) and 30 crayfish matched for size and sex were kept as controls and maintained for 6 months. Tagging had no significant effect on survival, moulting or growth of crayfish, and tag retention was 100%. The reader unit consists of an antenna coil mounted on a pole and designed to be moved over the streambed to search for tagged crayfish. Efficiency testing indicated that more than 80% of tags were identified and located when hidden within different stream microhabitats.     

Relative growth and onset of morphological sexual maturity of the freshwater crab Sylviocarcinus pictus in a river of the Caatinga of northeastern Brazil

The aim of this study was to investigate the relative growth and onset of morphological sexual maturity of the freshwater crab Sylviocarcinus pictus. Specimens were collected every month from October 2013 to September 2014, at night, on a stretch of the river Guaribas, Piauí, Brazil. Crabs were sexed and their carapace width (CW, independent variable), carapace length (CL), cheliped propodus length (PL) and height (PH), gonopod length (GL), and abdomen width (AW) (dependent variables) were measured. These measurements were related to characterise relative growth and possible sex differences. On average males were larger than females (p = 0.0001). Size at the onset of morphological sexual maturity was defined by relating CL vs. PL for males (30.82 mm) and CL vs. AW for females (28.63 mm). These are considered secondary sexual characters and reflect initial size at morphological sexual maturity with greater precision. The differential cheliped growth of males may be related to courting and disputes with other males, while the allometric growth of the abdomen of females indicates increased probability of reproductive success.