M. Sáez-Royuela

The possibilities for artificial incubation of white-clawed crayfish (Austropotamobius pallipes Lereboullet) eggs: comparison between maternal and artificial incubation

Abstract The development of artificial incubation techniques for freshwater crayfish eggs and the incorporation of these practices to the working scheme in production centres would have numerous advantages. This study evaluates the efficacy of one particular device, designed by this research group, for the artificial incubation of white-clawed crayfish ( Austropotamobius pallipes ) eggs. Comparisons between maternal and artificial incubation demonstrated the suitability of the tested system for artificial incubation for eggs of this species, during a period of 42% of the total duration of the embryonic development. Overall survival rate to juvenile stage 2 was significantly higher ( P

Effects of management on survival and growth of Stage 2 juvenile freshwater signal crayfish (Pacifastacus leniusculus Dana) under laboratory conditions

Abstract Four experiments were carried out in order to evaluate survival and growth rates of Stage 2 juvenile Pacifastacus leniusculus under different management conditions: effects of offspring origin (artificial incubation, maternal incubation under laboratory conditions and maternal incubation under natural conditions), of different shelter availability, of water circulation systems (partially re-circulated and full flow-through), and effects of certain flow rates. Juveniles kept singly, rather than in groups, had higher survival rates. However, when juveniles were in groups, they showed faster growth. Offspring from artificial incubation did not show significant differences in survival and growth rates from those from maternal incubation. The addition of pebbles as shelter did not improve survival rates. The use of a full flow-through system allowed significantly higher survival and growth rates. A flow rate of 1 l/min improved the survival rate in comparison with 6 l/min, but not growth. In general, the highest mortality occurred during the first 40–60 days of the experiments, although a great variation in the final results was observed.

Effects of shelter type and food supply frequency on survival and growth of stage-2 juvenile white-clawed crayfish (Austropotamobius pallipes Lereboullet) under laboratory conditions

Two shelter substrates (fibre-cement sheets and PVC pipes) and two foodsupply frequencies (once and twice daily) were tested on white-clawed juvenilecrayfish in two separate experiments performed under laboratory conditions.Juvenile crayfish were maintained at an initial density of 50 animals persquaremetre in a flow-through system and fed on fresh Daphniapulex and a feed formulated for rainbow trout. After 120 days,highersurvival (50.5%), but lower growth, was obtained when fibre-cement sheets wereprovided as shelter. A comparison between food supply frequencies showed abetter survival rate (60.5%) when food was provided twice per day althoughtherewere no differences in growth after 80 days of trial. The number of animalswith chela autotomy is positively correlated (r between 0.33 and 0.48 depending ontreatments) with decreases in survival rate. The combination of adequate shelterand frequency of food supply could reduce the agonistic behaviour of juvenilecrayfish.

Effects of different thermal treatments during embryonic development on the artificial incubation efficiency of crayfish (Austropotamobius pallipes Lereboullet) eggs. Control of the embryogenetic duration and implications for commercial production

Summary The development and improvement of artificial incubation techniques for freshwater crayfish eggs and their incorporation into the working schedule of breeding centres is of great interest for commercial production. Factors such as the water circulation system, flow rate, thermal treatment, etc., could strongly influence the success of the process. The present study attempts to test the possible influence of one of these variables, the thermal regime, on both the duration of embryonic development and the efficiency rates obtained in the artificial incubation of white-clawed crayfish (Austropotamobius pallipes) eggs. Four different thermal treatments were tested (three of them included a period at low temperature: 4°-5°C). Survival rates to juvenile stage 2 were similar in the four cases, ranging between 66.7 and 72.7%. We conclude that water cooling (an expensive management procedure) is not necessary in astacid breeding centres provided that egg development takes place at moderately low temperatur...

EFFECTS OF DIFFERENT THERMAL TREATMENTS ON THE MATERNAL INCUBATION EFFICIENCY OF THE ASTACID CRAYFISH AUSTROPOTAMOBIUS PALLIPES (LEREBOULLET,1858) UNDER CONTROLLED CONDITIONS

[Adult freshwater crayfish, Austropotamobius pallipes, were maintained in the laboratory in such a way that mating, spawning, and maternal egg incubation took place under controlled conditions. This allowed to obtain data on reproductive biology from spawning to stage 2 juveniles. Three different thermal treatments were tested during embryonic development: a constant temperature of 11°C, ambient room temperature, and the incorporation of a cold period (3 weeks at 4°C). Females used in the three treatments tested were of a similar size (Mean Carapace Length ± Mean Standard Error = 34.06 ± 0.11 mm). Stage 2 juvenile production was not significantly different among the three regimes applied. The highest mean number of stage 2 juveniles per female (23) was obtained in animals maintained at constant temperature. Statistical differences were not detected, neither with regard to reproductive efficiency, in which the best value (33%) again was obtained at constant temperature. Although thermic manipulation thus did not provide better results as regards efficiency, this practice allowed to obtain stage 2 juveniles in different batches, spaced in time. Cangrejos de rio de la especie Austropotamobius pallipes se mantuvieron en laboratorio durante la fase reproductiva. De esta forma, apareamiento, puesta y todo el proceso de incubacion maternal de los huevos tuvieron lugar bajo condiciones controladas. Esto permitio la obtencion de datos biologicos reproductivos desde la puesta hasta el segundo estado juvenil. Durante el desarrollo embrionario, se ensayaron tres tratamientos termicos: temperatura constante de 11°C, temperatura ambiente y la inclusion de un periodo frio (3 semanas a 4°C). Las hembras presentaron una talla similar en los tres tratamientos (Longitud Media de Cefalotorax ± E.S.M. = 34,06 ± 0,11 mm). La produccion de juveniles estado 2 no mostro diferencias significativas entre regimenes termicos, aunque el numero medio mas alto obtenido por hembra (23) correspondio a animales mantenidos a temperatura constante. Igualmente, tampoco fueron detectadas diferencias significativas en los resultados de eficiencia reproductiva. El valor mas elevado (33%) fue obtenido con temperatura constante. Aunque la manipulacion termica no mejoro significativamente los resultados de eficiencia, esta practica permite la obtencion de juveniles estado 2 en diferentes lotes dentro de amplios margenes de tiempo., Adult freshwater crayfish, Austropotamobius pallipes, were maintained in the laboratory in such a way that mating, spawning, and maternal egg incubation took place under controlled conditions. This allowed to obtain data on reproductive biology from spawning to stage 2 juveniles. Three different thermal treatments were tested during embryonic development: a constant temperature of 11°C, ambient room temperature, and the incorporation of a cold period (3 weeks at 4°C). Females used in the three treatments tested were of a similar size (Mean Carapace Length ± Mean Standard Error = 34.06 ± 0.11 mm). Stage 2 juvenile production was not significantly different among the three regimes applied. The highest mean number of stage 2 juveniles per female (23) was obtained in animals maintained at constant temperature. Statistical differences were not detected, neither with regard to reproductive efficiency, in which the best value (33%) again was obtained at constant temperature. Although thermic manipulation thus did not provide better results as regards efficiency, this practice allowed to obtain stage 2 juveniles in different batches, spaced in time. Cangrejos de rio de la especie Austropotamobius pallipes se mantuvieron en laboratorio durante la fase reproductiva. De esta forma, apareamiento, puesta y todo el proceso de incubacion maternal de los huevos tuvieron lugar bajo condiciones controladas. Esto permitio la obtencion de datos biologicos reproductivos desde la puesta hasta el segundo estado juvenil. Durante el desarrollo embrionario, se ensayaron tres tratamientos termicos: temperatura constante de 11°C, temperatura ambiente y la inclusion de un periodo frio (3 semanas a 4°C). Las hembras presentaron una talla similar en los tres tratamientos (Longitud Media de Cefalotorax ± E.S.M. = 34,06 ± 0,11 mm). La produccion de juveniles estado 2 no mostro diferencias significativas entre regimenes termicos, aunque el numero medio mas alto obtenido por hembra (23) correspondio a animales mantenidos a temperatura constante. Igualmente, tampoco fueron detectadas diferencias significativas en los resultados de eficiencia reproductiva. El valor mas elevado (33%) fue obtenido con temperatura constante. Aunque la manipulacion termica no mejoro significativamente los resultados de eficiencia, esta practica permite la obtencion de juveniles estado 2 en diferentes lotes dentro de amplios margenes de tiempo.]

Duration of egg storage at different temperatures in the astacid crayfish Pacifastacus leniusculus: critical embryonic phase

Abstract The critical phase that would limit duration of egg storage in the astacid crayfish Pacifastacus leniusculus was investigated. Weekly monitoring was conducted during an 84-day period of storage at three different constant temperatures (15.5±1, 10.5±1.5 and 4±0.5 °C). After artificial incubation, stage 2 juveniles were only obtained from the lowest storage temperature, the sole treatment in which eggs did not reach the critical embryonic stage by the end of the storage. This limiting stage occurs at phase XII (embryo with pulsating heart) when embryogenesis of stored eggs ceased and phase XIII (eyed stage) was not reached. Eggs were also stored at a constant refrigeration temperature (4±0.5 °C) for periods ranging from 84 to 126 days. Mean survival rates to juvenile stage 2 were acceptable (approximately 50%) and different batches of juveniles were obtained over a 3-month period, depending on the duration of storage. The combined use of storage and artificial incubation techniques could have important applications to the development of astacid crayfish culture.

Successful storage and transport of eggs of the white-clawed crayfish (Austropotamobius pallipes Lereboullet)

Embryonated eggs of theEuropean native white-clawed crayfish Austropotamobius pallipes Lereboullet weresubjected to three periods of storage usingpolystyrene boxes and, afterwards, artificiallyincubated. At the end of the longest storage(42 days) survival rate was 98.3%, with 65%developed to stage 2 juvenile. Differentstorage periods allowed the staggeredproduction of juvenile batches within a monthperiod. The same containers used for storagewere also suitable for transport.

Effects of the presence or absence of males throughout spawning and maternal incubation on the reproductive efficiency of astacid crayfish (Austropotamobius pallipes) under controlled conditions.

Summary The separation of females and males after mating is a usual practice when the reproductive phase of astacids takes place under controlled conditions and is carried out to avoid egg losses due to male disturbance during spawning and embryonic development. In order to determine the possible effects of male presence on reproductive efficiency, two treatments were tested in the white-clawed crayfish (Austropotamobius pallipes): females alone, and females and males together throughout egg laying and embryonic development, respectively (mean female carapace length = 36.35 ± 0.57 mm). The mating period lasted 19 days. The overall rate of insemination was 98.3%. After 200 days of the experiment, a similar average number of stage-2 juveniles per female was obtained in the two treatments: 48.9± 7.1 in females alone and 46.3± 5.9 with males. In view of the difficulties in separating males and females, and the apparent lack of effect on reproductive efficiency, continued use of the practice should be reconsidered.

Decapsulated Artemia Cysts: A Suitable Dietary Supplement for Juvenile Tench (Tinca tinca L.)

There are no specifically formulated dry foods for tench (Tinca tinca L.), which forces farmers to use diets formulated for other fish species. This has major drawbacks, such as high mortality, slow growth, and body deformities. A 120 day experiment was performed with five-month-old juvenile tench (initial mean weight: 0.388 g; total length: 31.78 mm) to evaluate decapsulated Artemia cysts as a supplement to a dry diet for other fish species. Three treatments, differing in the daily supplement, were tested: 1,800 freshly hatched nauplii, 1,800 cysts, and 300 cysts per g of tench biomass. Final survival ranged between 95.3% and 97.9%. Juvenile tench that received the supplement of 1,800 decapsulated Artemia cysts had a specific growth rate (1.28), weight (1.83 g), and total length (52.30 mm) significantly higher than those with the same amount of nauplii. The lowest supplement (300 cysts/g of fish biomass) allowed significantly lower growth and higher condition coefficient (1.40) than the rest. Animals with body deformities (1.06%) were only recorded in the groups that received the lowest cyst supplement. Results showed Artemia cysts are a suitable dietary supplement for juvenile tench, being an advantageous alternative to live nauplii.

EFFECTS OF STAGE 2 JUVENILE REMOVAL FREQUENCY ON FINAL SURVIVAL RATES IN ARTIFICIAL INCUBATION OF CRAYFISH EGGS (PACIFASTACUS LENIUSCULUS DANA. ASTACIDAE)

Abstract In artificial incubation of astacid crayfish eggs, stage 2 juveniles must be removed by hand from incubators and a significant decrease in survival rates has been recorded between hatching (stage 1) and the first moult (stage 2). To reduce these losses, eggs of Pacifastacus leniusculus were incubated at a density of 6.6 cm−2 and different removal frequencies of stage 2 juveniles from the incubators were tested: every 5, 4, 3, and 2 days, daily and only once at the end of incubation. Formaldehyde was used to control growth of fungi. The best final survival rate (88.6%) was obtained when stage 2 juveniles were removed daily from the incubators. There were no significant differences nor between removals every 2 and 3 days (79.6% and 76.5%, respectively) neither between 4 and 5 days (72.6% and 69.8%, respectively). Considering all treatments, final survival rates decreased as juvenile removal was delayed up to only one removal at the end of incubation.