Moult Increment Research Articles

EFFECTS OF RATION SIZE AND TEMPERATURE ON MOULT INCREMENT AND METABOLIC PARAMETERS OF JUVENILE NOBLE CRAYFISH, ASTACUS ASTACUS

A laboratory experiment was carried out to test the combined effects of ration size (1 vs 3% body weight, b.w.) and temperature (15 ± 2 vs 22 ± 2 °C) on moult increment and metabolic parameters of 80 juvenile noble crayfish (Astacus astacus). The maximum daily consumption (Cmax) and respiration rate (R) were used to calculate the growth scope (i.e. the difference between maximum daily energy consumption and energy costs at a given temperature). The conversion of R into a food-equivalent unit allowed the comparison with Cmax. Results showed that crayfish obtained the maximum moult increment when fed 3% b.w. while temperature seemed to play a less relevant role on growth rate per moult, affecting only the moulting frequency. Crayfish A. astacus fed ad libitum showed a relative insensitivity to the metabolic parameters (oxygen uptake, R and Cmax) within the analysed range of temperatures, possibly as a reflection of this “species” distribution across a broad variety of habitats with different thermal regimes. In the present study, A. astacus displayed characteristics proper of a K-selected species, as slow to moderate growth.

Replacement of adult maxillary jaws in Eunicida (Polychaeta)

Replacement of adult maxillary jaws is reported for Diopatra aciculata. The process is similar to arthropod moulting, commencing with apolysis or retraction of the epidermal cells from the inner surface of the old cuticle, followed by formation of the new cuticle. This results in the jaw-in-jaw or pharate state. Ecdysis or shedding of the old cuticle takes place without any splitting or damage as evidenced by complete, fully articulated shed jaws found in the gut. Newly moulted maxillae are soft and white until they become sclerotized. The new jaws are about 1.4 times the size of the old ones (moult increment). The same process is expected to occur in all extinct and extant Labidognatha. The Recent Lumbrineridae maxillae may not be of the labidognath type, but probably moult in the same manner. Occasional finds of pharate jaws of the extinct Placognatha indicate that they underwent similar jaw replacement. Not enough is known about Prionognatha, although shedding before replacement may occur. Jaw replacement in Ctenognatha, where the new elements form in sac-like epithelial structures ventrolateral to the existing maxillae, is probably limited to this group.

Growth of juvenile lobster Homarus americanus off the Magdalen Islands (Quebec, Canada) and projection of instar and age at commercial size

Juvenile American lobster Homarus americanus were quantitatively surveyed in the southeast Baie de Plaisance, Magdalen Islands, from 1995 to 2004. Lobster were collected by SCUBA, in summer and/or early fall after the annual settlement period. Growth for up to 3 yr following settlement was assessed by modal analysis of carapace length (CL)-frequency distributions and was confirmed for the first year by in situ rearing of Stage IV lobster collected from the plankton. In every sampling year, some modes (attributed to instars) were apparent in CL-frequency distributions up to 50 mm CL (estimated to be Instar XVI on average). The mean percent molt increment declined gradually from about 23% at Instar IV to about 15% at Instar XV. Strong year-classes could be tracked reasonably well for up to 2-3 yr after settlement. From this point, we projected growth to fishery recruitment and suggest that lobster reach commercial size at a higher instar and older age than previously believed. This is the first study to explain lobster juvenile growth in such detail, and it constitutes an essential step toward the understanding of potential settler-to-recruit relationships.

Growth, reproductive cycle, and movement of berried European lobsters (Homarus gammarus) in a local stock off southwestern Norway

Abstract Agnatt, A-L., Kristiansen T. S., and Jorstad K. E. 2007. Growth, reproductive cycle, and movement of berried kuropean lobsters (Homarus gammarus) in a local stock off southwestern Norway. – ICES Journal of Marine Science, 64: 288–297. The Norwegian fishery for the European lobster (Homarus gammarus) collapsed between 1960 and 1980, to <10% of its pre-1960 level, and since then the spawning stock seems to be too low to generate good recruitment. In 1998, a project to evaluate the feasibility and effect of protecting berried female lobsters as a management restriction was initiated. The study area selected was previously an important fishing ground in Kvitsøy off southwestern Norway, and 125 000 hatchery-reared juveniles were released between 1990 and 1994. From spring 1998 to spring 2000, a total of 942 wild and 480 cultured berried females was purchased from fishers, individually tagged with a streamer-tag, and released. The proportion of berried females in the landings varied annually from 19 to 58% for wild females, and from 22 to 44% for cultured females. By spring 2000, 23% of the tagged females had been recaptured at least once, and 3% twice or more. Average moult increment was 7 mm carapace length (CL), independent of pre-moult size in both wild and cultured females. Reproduction (spawning) and growth (moulting) alternated in a 2 y cycle for >90% of the females. A small number moulted and spawned a few weeks after hatching. More than 95% of the recaptures were taken within a radius of 1 km of the release area. Egg production varied considerably between seasons. Reproductive potential (RP) of landed berried females underestimated egg production compared with what was actually produced (AE). For the entire period, RP was estimated to be about 15.0 million eggs, and AE to be 17.2 million eggs. Cultured females contributed 27% of AE. To reduce the fishing mortality in a heavily fished and depleted population is vital. A ban on landing berried females would be a valuable first step in attempting to increase the spawning biomass.

Growth rate of the crab Dissodactylus crinitichelis Moreira, 1901 (Crustacea: Decapoda: Pinnotheroidea) under laboratory conditions

The goal of the present study was to investigate the growth rate of the crab Dissodactylus crinitichelis, its molt increments, and the duration of the intermolt intervals under laboratory conditions, focusing on differences between sexes and between juvenile and adult phases. Crabs were collected at Flamengo Beach, Ubatuba, São Paulo State, Brazil, by scuba divers. In the laboratory, individuals were maintained in isolation and fed nauplii of Artemia sp. daily. The sex and carapace width of exuviae and dead crabs were recorded. During the juvenile phase, mean growth was 11.8 ± 2.7% in males and 11.2 ± 3.6% in females, with their respective intermolt intervals 25.4 ± 9.2 and 26.4 ± 8.3 d (mean ± SD). After reaching morphological sexual maturity, the intermolt intervals increased to 33.4 ± 10.1 d in males and 32.7 ± 10.4 d in females, and the growth rates of both sexes slowed to 6.4 ± 1.9% in males and 5.7 ± 1.6% in females. There was a significant decrease in molt increment and an increase in intermolt intervals associated with the maturation from juveniles to adults, evidencing differential energy allocation during the last phase of ontogeny.

Larval molting and growth of the Japanese spiny lobster Panulirus japonicus under laboratory conditions

Ten newly hatched phyllosoma of Panulirus japonicus were cultured individually to monitor body length (BL) and intermolt period, and 2000 were cultured in groups to sample specimens for measurement of body weight. Phyllosoma were fed with Artemia and mussel gonad; the culture seawater temperature was 24–26°C. The individually cultured phyllosoma showed an increment in body length by the first molt of approximately 0.5 mm, and the molt increment increased to approximately 1 mm at 5 mm BL; it was constant to 15 mm BL. The reafter, the molt increment increased exponentially. The duration of the first instar was 6–7 days. Instar duration increased with development up to approximately 2 weeks at the 20th instar (≈16 mm BL) and then became constant. Of the 10 larvae reared individually, five metamorphosed to the puerulus stage. The entire phyllosoma life ranged from 245–326 days (mean 289.0 days), and the number of instars ranged from 22–29 (mean 26.2). Body length in the final instar ranged from 28.50–33.10 mm (mean 30.280 mm). For the phyllosoma cultured in groups, relationships between BL and wet/dry body weights (WW/DW, mg) were expressed as exponential equations: WW=0.0686BL2.2023 and DW=0.0209BL2.1905.

The Effect of Potassium Concentration in Inland Saline Water on the Growth and Survival of the Western King Shrimp, Penaeus latisulcatus Kishinouye, 1896

The survival, growth, and condition of the western king shrimp, Penaeus latisulcatuswere measured for 42 days when grown in marine water and inland saline water with four different concentrations of potassium: 100%, 80%, 60% or 40% of the concentration of potassium in marine water (IS100, IS80, IS60, and IS40). Shrimp survival and cannibalism frequency decreased with decreasing potassium concentration, with final shrimp survival in IS100 significantly higher (P < 0.05) than in IS60 and IS40 and significantly higher (P < 0.05) in MW and IS80 than in IS40. Specific growth rate (SGR), moult increment, and diet ingestion rate of shrimp were significantly higher (P < 0.05) in shrimp grown in marine water than the other water types. At the conclusion of the trial, exoskeleton mineral content of shrimp in IS100 and IS80 was significantly higher (P < 0.05) than in IS60 and IS40. Tail muscle moisture content of shrimp in IS60 and IS40 was significantly higher (P < 0.05) than in the other water types, suggesting a depletion of tail muscle energy reserves in IS60 and IS40. This trial demonstrates the necessity of fortifying potassium-deficient inland saline water to allow the culture of western king shrimp. Furthermore, a potassium concentration greater than approximately 76% of that in marine water and a Na/K ratio of less then 39 appear to be necessary to maintain a comparable level of shrimp survival, as in marine water. However, the slower growth and reduced molt increment of shrimp in inland saline water with 100% and 80% potassium compared to shrimp in marine water demonstrates the presence of other limiting factors.

Effects of temperature and water calcium concentration on growth, survival and moulting of freshwater crayfish, Paranephrops zealandicus

Two 3-month experiments were conducted to investigate the effects of temperature and water calcium concentrations on growth, survival and moulting of freshwater crayfish ( Paranephrops zealandicus). Both experiments were conducted using three replicates of five treatments (water temperatures of 14, 16, 18, 20 and 22 °C for Experiment 1 and water calcium concentrations of 0, 5, 10, 30 and 80 mg/L for Experiment 2). Growth rates increased with water temperature (maximum specific growth rate = 0.57) but were unchanged with increased water calcium concentration. Variability in growth rates decreased with increased water calcium concentrations. Survival decreased as water temperatures exceeded 16 °C and increased with water calcium concentrations above 10 mg/L. Inter-moult period decreased from > 90 ± 20 days at water temperatures of 14 °C to ∼ 40 ± 10 days at water temperatures > 20 °C. Moult increment of the crayfish was unaltered by either water temperature or water calcium concentrations. The optimum water temperature for productivity under conditions employed was 16 °C.

Growth and moulting of captive Panulirus homarus homarus in Kenya, western Indian Ocean

Panulirus homarus homarus is the most widely distributed of the three P. homarus subspecies and is the second most important spiny lobster in the Kenyan lobster fishery after Panulirus ornatus. Growth and moulting of lobsters held in concrete tanks with a flow‐through sea‐water system and at ambient temperatures, were monitored for 18 months (October 2001 ‐ March 2003). Both moult increment and moulting frequency were inversely correlated with size. Mean moult increment ranged from 4 mm in the 36–45 mm carapace length (CL) size class to 0.6 mm in the 86–95 mm CL size class. Mean intermoult period increased from 49 days in the 46–55 mm CL size class to 66 days in the 76–85 mm CL size class. Growth rates were 19% and 46% higher for males and females, respectively during the south‐east monsoon (low temperature) season than during the north‐east monsoon (high temperature) season. A shift in energy use from growth to reproduction rather than the influence of temperature was responsible for the variation in the growth rates between the two seasons. Marking‐induced injury caused a significant 65% growth reduction in the affected individuals. Mean moult increments calculated for most size classes of uninjured lobsters were comparable to those observed in the subtropical P. homarus rubellus reared in the laboratory in South Africa but smaller than those reported in the Indian P. homarus under similar conditions.

Life cycle of Agapetus fuscipes (Trichoptera, Glossosomatidae) in a first-order upland stream in central Germany

The number of immature stages and the seasonal patterns of development are basic life history features of a stream dwelling species and knowledge about these important components are essential for understanding its adaptations to its dynamic environment. The life cycle of Agapetus fuscipes (Trichoptera, Glossosomatidae), one of the dominant scrapers in the upper and middle reaches of the Breitenbach, a first-order upland stream in central Germany, was analysed. The pronotum length and the relationship between pronotum length, larval biomass and case length showed seven distinct larval instars, contrary to earlier findings from the Breitenbach. In addition to a few trichopteran species from other functional feeding groups, A. fuscipes is the only scraping caddis fly reported to have more than five larval instars. The moult increments of pronotum length and larval biomass were distinctly lower than in glossosomatid species with five larval instars. A. fuscipes is clearly univoltine in the Breitenbach. First-instar larvae were found from July to the beginning of December, and second-instar larvae from July to January. At the beginning of December the population consisted of the instars I to V, and development did not cease during winter. The sixth-instar larvae occurred mostly in January, and the seventh-instar larvae were never present before January. The prepupae and pupae occurred in April. The last pupae were found at the beginning of September, although most of the emergence took place in June and July. At least five different immature stages with different ecological demands were present at any time throughout the year. The ecological advantage having two additional larval instars compared to other glossosomatid species may be to compensate for the high rate of mouthpart wear that occurs while the larvae feed on the rough Bunter Sandstone substratum. A further advantage may be to spread the risk of high mortality under unfavourable environmental conditions.

Effects of temperature and salinity on survival and growth of the amphipod Hyale crassicornis (Gammaridea, Hyalidae)

This study explored the survival and growth of the marine amphipod Hyale crassicornis under different conditions of ambient temperature and salinity in the laboratory. In 96‐h exposure experiments at a salinity of 30, H. crassicornis tolerated temperatures between 6 and 28°C (>90% survival). The 96‐h LT50 value (median lethal temperature) at high temperature range for the amphipod was 32°C. The values at low temperature range for adults and juveniles were 3.2 and 4.2°C, respectively, indicating that adults have a higher tolerance to low temperature than juveniles. At 25°C, the amphipods tolerated salinities between 10 and 50 (with >80% survival in 96 h). The 96‐h LS50 values at high and low salinity ranges were 56 and 2, respectively. Growth of the juveniles from instars 1 to 6 was determined under different combinations of temperature and salinity. Growth rate of juveniles cultured at 25°C and a salinity of 20 was the highest (0.114 mm day−1) among the combinations of 15–25°C and 10–40 salinity. The moult increment of body length was affected by both temperature and salinity. Yet the intermoult duration of the amphipods was affected by temperature only but not by salinity.

Use of length-based models to estimate biological parameters and conduct yield analyses for male Dungeness crab (Cancer magister)

Length-based models were developed for the male Dungeness crab (Cancer magister) population on the Fraser delta near Vancouver, British Columbia. The models incorporate the probability of moulting, moult increments, natural mortality during moulting and non-moulting periods, direct fishing mortality, and handling mortality that occurs when sublegal-sized crabs are caught and released. The models were used to investigate how long-term yield might be affected by the combination of handling mortality and an intensive fishery. The models were calibrated to survey data, and key biological parameters were estimated. The probability of moulting is near one for male crabs in the 130- to 150-mm carapace width range and decreases as crabs get larger. There is a 70.1% probability a crab will survive the 1-month period beginning with a moult. The non-moulting natural mortality rate is 0.97 year–1. When handling mortality is incorporated into the model, yield per recruit increases with the exploitation rate until it reaches approximately 94%. F0.1 is equivalent to 70%. An approach was developed to calculate the threshold ratio of discarded to retained crabs beyond which fishing would reduce the long-term yield.

Effects of temperature on metabolism, growth and growth efficiency of Thysanoessa longipes (Crustacea: Euphausiacea) in the Japan Sea

Growth (assessed from intermolt period and molt increment) and metabolism (oxygen consumption) of juvenile and adult Thysanoessa longipes from central Japan Sea were determined at eight different temperatures ranging from 0 to 14 � C. The intermolt period shortened progressively as temperature increased from 0 to 14 � C. The molt increment was not assessed satisfactorily in the rearing experiments, and therefore this was estimated from the natural growth curve and habitat temperature, combined with laboratory-obtained intermolt data. Oxygen consumption rates increased exponentially from 0 to 8 � C and then leveled off. From these results, the growth was expressed as a function of temperature and body size and metabolism as a function of temperature. Because of the differential effects of temperature on growth and metabolism, the net growth efficiency [NGE: 100 � growth/(growth + metabolism)] changed with temperature. The temperature at which T. longipes attained maximum NGE varied from 0 to 8 � C, depending on the body length of specimens of 5, 10, 15 and 20 mm. The present results are compared with our previous data on Euphausia pacifica in relation to the body composition and habitat usage of these two trophically important species in the food web of the Japan Sea.

Molt and growth of an estuarine crab, Chasmagnathus granulatus (Brachyura: Varunidae), in Mar Chiquita coastal lagoon, Argentina

Summary Juvenile and adult growth of Chasmagnathus granulatus was studied in the laboratory in terms of molt increment in size (MI) and the intermolt period (IP), comparing data obtained from short-term (STE) and long-term (LTE) laboratory experiments. Crabs in a pre-molt condition were collected for STE, including the entire size range of the species. Larger crabs remained in the laboratory no more than 14 days; the average time to molt was 5.8 ± 3.1 days. We registered the molt of 94 females, 64 males and 34 undifferentiated juveniles and calculated their MI. Moreover, 24 males and four females were reared in the laboratory over 3 years (LTE). Hiatt diagrams did not show sex-specific differences between juveniles of both sexes, but revealed differences between juveniles and adults in each sex as well as between adults of both sexes. The MI decreased gradually with size; this pattern was described with a quadratic model. The IP increased exponentially with size. The presence of regenerating limbs diminished the MI. The abdomen of females reached its final shape and maximum relative width at functional maturity. Growth curves for both sexes were calculated using the von Bertalanffy model, but this model yielded an underestimation of the actual maximum size of this crab.

Androgenic gland implantation promotes growth and inhibits vitellogenesis in Cherax quadricarinatus females held in individual compartments

Summary Androgenic glands (AGs) were implanted into young female red claw crayfish, Cherax quadricarinatus, with the aim of investigating the role played by the AG in the balance between growth and reproduction under conditions of minimal social interaction (individual compartments). The growth rate of the females with AG implants was significantly higher than that of the control non-implanted females (0.11 ± 0.03 g/day vs. 0.08 ± 0.02 g/day). This difference was attributed to the larger molt increments and slightly shorter molt intervals of the females with implants vs. the control females. At the end of the experiment (538 days), the mean weight of the implanted females was significantly higher than that of the control females (64.58 ± 18.24 g vs. 51.07 ± 12.71 g, respectively), a lead of 26.4% for the implanted females that started 91 days after implantation and became significant at 153 days after implantation. By that time, 55.5% of the implanted females had developed typical male secondary characters, such as the red patch on the propodus. The shift of energy from female reproduction to growth was further demonstrated by the level of expression of the vitellogenin gene in the hepatopancreas: gene expression was high in control females but lower by several orders of magnitude in the AG-implanted females, as shown by real time RT-PCR relative quantification. Confirmation of these findings was provided by an ELISA test, which showed that the level of vitellogenic cross-reactive protein in the hemolymph of AG-implanted females was significantly lower than that in intact females. The significant growth promotion in AG-implanted females was clearly not due to social interaction. It may be attributed to a direct growth factor—like the effect of androgens in vertebrates—in combination with an indirect effect, through the shift of energetic investment from reproduction and vitellogenesis to growth. Since the AG implant had a more marked effect on molt increment than on molt interval, it seems likely that the AG acts as a growth promoter rather than as a molt enhancer.

주름꽃게 (Liocarcinus corrugatus) 유생의 성장과 생존에 대한 온도의 영향

The effects of temperature on the growth of larvae of wrinkled swimming crab (Liocarcinus corrugatus) under controlled laboratory conditions of 15, 20 and <TEX>$24^{\circ}C$</TEX> were investigated (33.5 psu: 12L: 12B). Each specimen was maintained individually, the instar size was determined from exuvia, and the survival and intermolt period of each instar were recorded. There were no significant differences (P>0.05) in the survival rates at 15, 20, and <TEX>$24^{\circ}C.$</TEX> Comparison of survival over the first 27 days between the three temperature regimes showed significant differences (P<0.001). The intermolt period increased with the instar number, and was greatly extended at the lowest temperature. The molt increment varied little with temperature, and had a mean value of <TEX>$21.35\%$</TEX> over the whole study. Temperature had little effect on survival and molt increment.

Size rank and growth potential in redclaw crayfish (Cherax quadricarinatus): are stunted juveniles suitable for grow-out?

Considerable size variation emerges at an early stage among redclaw (Cherax quadricarinatus) juveniles. In order to explore whether juveniles from different size fractions of the same population differ in their growth potential, they were reared individually, in the absence of social effects. In the first experiment, post-release siblings were reared for 5 weeks and then categorized into three size fractions: small, med-sized and large. Subsequently, juveniles of each size fraction (n=24, 18, and 18, respectively) were reared in individual cells for 46 days and their moult increments and moult intervals were compared. In addition, the growth indices of the med- and large-sized juveniles were compared with those of juveniles from other broods that were similar in age and size but belonged to a different size fraction, in order to separate the effect of absolute size from that of size rank. In a second experiment, juveniles from the small-, med- and large-size fractions (n=21) of a commercial nursery-reared population were individually reared for 14 weeks and their growth indices were compared. Survival of individuals from the small-size fraction was low, particularly in the first experiment, and increased with fraction size. However, small-sized juveniles did not show reduced growth potential and even grew at a faster rate than large-sized juveniles. The results indicate that social interactions plays an important role in the development of size variation, and that small juveniles have the potential to grow rapidly when reared in individual compartments. Overall, the size rank was a poor predictor of growth potential.

Growth, survival, haemolymph osmolality and organosomatic indices of the western king prawn (Penaeus latisulcatus Kishinouye, 1896) reared at different salinities

The growth, survival, haemolymph osmolality and organosomatic indices of the western king prawn, Penaeus latisulcatus, (2.95±0.26 g mean initial weight), were measured when reared at 10, 22, 34 and 46 ppt salinity for 60 days. Mean final weight, total length and specific growth rate (SGR) of the prawns were highest at 34 ppt. Rearing at different salinities did not alter moult increments and intermoult periods of the prawns. One hundred percent mortalities were observed at 10 ppt.Survival was highest at 22 ppt and food conversion ratios were significantly lowest (P<0.0.5) in prawns cultured at 22 and 34 ppt. Haemolymph osmolality increased with the increase in medium salinity and physiological age of the prawns. Isosmotic points calculated from regression between haemolymph and medium osmolality were 28.87, 29.46 and 31.73 ppt at 0, 20 and 60 days of culture, when body weights were 2.95±0.26, 4.02±0.47, 5.79±0.64 g respectively. After 60 days of culturing, hepatopancreatic moisture levels increased with the increase in salinity, whereas tail moisture levels remained unchanged. Wet and dry hepatosomatic indices were highest at 22 ppt. Wet tail muscle index was highest at 34 ppt, whereas dry tail muscle index did not change by any salinity levels. The results suggest that the optimum salinity range for rearing western king prawns ranges from 22 to 34 ppt and 10 ppt was unsuitable for culture.

Field Observations of Moulting and Moult Increment in the Red Land Crab, Gecarcoidea Natalis (Brachyura, Gecarcinidae), on Christmas Island (Indian Ocean)

Red land crabs, Gecarcoidea natalis (Pocock, 1888) are the most abundant land crabs on Christmas Island (Indian Ocean; 10?3(ys 105?4(yE), occurring at mean densities and biomasses from 0.4 to 1.8 crabs m-2 and 1.0 to 1.5 t ha-1 (Green, 1997). With the exception of some breeding-related activities (Hicks, 1985; Adamczewska & Morris, 2001) these crabs are completely terrestrial, and inhabit dry, shallow burrows throughout rain forest on the island. The largest males grow to > 120 mm carapace width and >500 g mass, but virtually nothing is known of growth rates and longevity in this species. Hicks et al. (1990) estimated that one, two, and three year old crabs were 9-20, 17-34, and 22-47 mm carapace width, respectively, and Hicks et al. (1984) guessed that the largest crabs were around 12 years old. Adult crabs moult in sealed burrows without access to free-standing water, but detailed observations of the moulting process, or moult increments, have not been reported for G. natalis. In this note I describe observations of moulting red crabs held in semi-natural conditions in primary rain forest near Murray Hill in the western area of the island. Red crabs were held in artificial burrows, which consisted of an inclined tunnel (a longitudinally cut section of PVC pipe with a timber cover) leading to an expanded chamber (a vertical section of larger diameter pipe). This chamber approximated the size of natural burrows for crabs in the 60-80 mm size range. The burrows were buried in the ground so that just the top of the chamber and tunnel entrance were exposed. The chamber was fitted with a rubber-lined cover, such that it formed a tight seal to trap moisture within the artificial burrow.

Combined Effects of Temperature and Diet on Growth and Survival of Young-of-Year Crayfish: A Comparison between Indigenous and Invasive Species

During a three-month rearing period we compared the (1) survival rate, (2) growth at moult, (3) number of moults, and (4) overall growth of the young of the year (YOY) of two crayfish species, the indigenous Austropotamobius pallipes and the nonindigenousProcambarus clarkii. One hundred twenty YOY of each species were reared in different test conditions, i.e., three temperatures (168 ,2 08, and 248C) combined with two different dietary regimes (either animal or detritus food items). The two species showed a number of similarities in their survival rate and growth format. First, in both species, animal proteins appeared fundamental for the YOY growth, because an exclusively vegetal diet significantly slowed growth rate. Thus, the YOY seemed to behave as obligate carnivores, and detritus appeared ineffective in sustaining growth. Then, an exclusively animal diet showed some deficiencies: exoskeleton appeared pale in its colour when the diet was composed of animal items only, possibly because carotenoids were lacking. Third, an increase in the temperature caused a decrease in both survival and growth rate, because it determined a reduction of the moult increment in both species. Differences between the two species were that the nonindigenous crayfish showed a significantly higher tolerance of elevated temperatures, and growth was significantly faster in P. clarkii than A. pallipes, being approximately double when the crayfish were reared with an animal diet. Together with other behavioural and ecological properties, these features make P. clarkii more competitive than A. pallipes in disturbed habitats and areas which are subject to man-induced modifications.