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Individual mating was compared with mating in groups under laboratory conditions using 64 females and 32 males of white–clawed crayfish (Austropotamobius pallipes). Mating in groups took place at a density of 24 animals/m2 placed in two 1m2 fibreglass tanks (16 females and 8 males/tank). Individual pairing was made in net plastic cubic boxes of 0.25 × 0.25 m bottom surface placed in 1m2 fibreglass tanks (8 boxes/tank). Percentages of mating and spawning were similar in both treatments (100 and 93.7% in groups and 96.9 and 93.7% in individual pairing). However, pleopodal egg number and survival rate 78 days after spawning (phase VIII-IX of embryonic development) were higher in females mated in groups (67 and 57.4%) than those individually inseminated (26 and 25.9%). Possible causes of lower egg survival rate of individually mated females are discussed.

In artificial incubation (AI) of astacid species, which have a long embryonic development, eggs have to remain during long periods without maternal care and it is recommended to remove the dead ones. With the aim to test the effect on final stage 2 juvenile production of different removal frequencies, four treatments were tested: removal every 4 days, every 7 days, every 10 days and no removal. Using an egg density of 2.2 eggs/cm2, stage 2 juvenile production rate was significantly better (70.3%) with removal every four days than with less frequent removals. However there were not detected statistical differences between the control (no egg removal) and the other treatments. The relatively low incubation density (2.2 eggs/cm2) could partially explain the general good results achieved, even when dead eggs were not removed.

With the aim of preserving and increasing endangered stocks of white-clawed crayfish, research on juvenile production has been carried out. Advantages in application of newly developed techniques of egg storage, transport and artificial incubation techniques are discussed. Eggs can be removed from maternal pleopods during the early stages of embryonic development and placed in artificial incubation devices. This practice avoids egg losses caused by aggressive contacts, female disease or death and the production of stage-2 juveniles in different batches by means of temperature manipulation. Furthermore transmission of pathogens from broodstocks to offspring can be minimised. Egg storage and transport have some advantages in the artificial reproduction of crayfish. Firstly, embryonic development continues under storage conditions and thus water and human effort can be saved during this period. Temperature plays an important role on both efficiency rates and duration of embryogenesis. Secondly, egg transport could facilitate restocking programs, as there is no need to move berried females to other habitats. To sum up, the combined use of artificial incubation and storage/transport techniques could have important applications to the development of astacid crayfish culture.

With the aim to evaluate the effect of different intervals of degrees-days on egg production of tench (Tinca tinca L.), 480 breeders were kept in 15 x 10 x 1 m bare concrete tanks from February until July and fed on commercial feed. Males and females were held together under natural photoperiod and temperature conditions. Ovulation was hormonally inducted (LH-RHa) in three groups at different degrees-days (group I: 1090, group II: 1175 and group III: 1536). In the groups I and II, a mean of 88% of females was injected, obtaining a 98% of positive response, without significant differences in the egg production between both groups (10.7% body weight, b.w.). With 1536 degrees-days, percentages of injected and stripped females were significantly lower. First stripping yielded a total of 9332 g of eggs (8.3% b.w.). A second hormonal induction was evaluated in each group at 1900, 2047 and 2111 degrees-days respectively. A mean of 85% of the initial females of the three groups received a second hormonal treatment, obtaining a 92% of positive response, without significant differences in egg production among the groups. The second stripping yielded an egg production (598 g, 5.9% b.w.) significantly lower than the first one. Relating to males, semen was obtained without hormonal induction throughout 50 days and the positive response was around 90%. With the exception of eggs obtained in the first induction of group III (1536 degrees-days), where overripening process was detected, further mean fertilization (over 80%) and hatching rates (around 35%) support the good quality of eggs and sperm. This study showed that the advantages of the broodstock’s maintenance in small concrete tanks are not only easiness of handling and possibilities of yield prediction, but also a good egg production at higher densities than in big earthen ponds.

The article presents information on a study on the effects of early suppression of cyst supplementation and different preparations of decapsulated Artemia cysts as a dietary supplement for juvenile tech. The supplements are for growth performance as well as body deformities reduction. It is stated that no significant differences were found in survival when different cyst supplements were provided.

Two 60-day experiments were carried out on tench ( Tinca tinca L.) from day 5 post-hatch. Density was 20 larvae L−1 and temperature 24 ± 0.5°C. In experiment 1, Artemia nauplii were the sole food, testing nauplii amounts and feeding frequency. High survival rates (between 79.5% and 95.5%) were obtained. Growth was faster as nauplii amounts were greater; the highest growth rate (11.00), weight (265.5 mg) and Fulton’s coefficient (1.40) were obtained when fish were fed in excess once a day, without significant differences from the growth obtained by feeding in excess of eight times a day. In experiment 2, a dry diet for marine fish was tested as a replacement for Artemia nauplii, following two transition protocols, one faster than the other; high survival rates (between 77.7% and 87.1%) were again obtained. The slower transition allowed a growth rate of 10.14, length of 23.1 mm, weight of 158.3 mg and a Fulton’s coefficient of 1.28, without significant differences from the faster transition. At all stages, growth values were significantly higher from feeding nauplii in excess as the sole food, but the required nauplii quantity was six times higher than the amount supplied to the animals fed the dry diet. [ABSTRACT FROM AUTHOR]

The study includes mating and spawning data of freshwater crayfish, Austropotamobius pallipes Lereboullet, obtained in four consecutive years (1987–1990). A total number of 586 wild-caught female A. pallipes in the 21.65 mm to 45.60 mm carapace length (CL) size were held under laboratory conditions at different dates in September–October. Initial densities at mating time were 21 and 24 crayfish/m² with a 1:2 male:female ratio. High percentages of mating were obtained (97.4–100%) except in 1989 (57.5%). In all years, most of the matings (90%) were concentrated in a period of 8–12 days with mean water temperatures between 12°C and 13.5°C. Spawning took place a few days after mating (minimum 2 days, maximum 14 days) at mean water temperatures between 8.2°C and 10.8°C. In the first 3 years, almost 100% of mated females spawned. However, in the fourth year (1990), when the mean size of crayfish was smaller, only 72.4% of mated females spawned. The mean number of pleopodal eggs was 64 (maximum 220, minimum 18). Egg diameter ranged between 2.30 and 3.25 mm (mean value 2.78 mm). Pleopodal egg number was positively correlated with carapace length (r = 0.72). [ABSTRACT FROM AUTHOR]

The egg development of the freshwater crayfish (Pacifastacus leniusculus Dana) under laboratory conditions is studied in this work from spawning to hatching. The sequence of its development is presented here, and the chronology of the different embryonic phases is established at one specific temperature (15.5 degrees +/- 1 degree C).