Search

Considering the concerns about the safety of the use of formaldehyde as antifungal agent, the effects of three alternative chemicals (potassium sorbate, copper hydroxide and magnesium chloride) were tested in the artificial incubation of signal crayfish (Pacifastacus leniusculus) eggs. Eight treatments were performed during 15 min every other day: formaldehyde at 3000 ppm (control), potassium sorbate at 5000 and 10000 ppm, copper hydroxide at 40, 60, 80 and 200 ppm, and magnesium chloride at 10000 ppm. Eggs were incubated in a flow through system at a density of 20 eggs·cm−2. After 61 days of incubation, the highest efficiencies were obtained with 200 ppm of copper hydroxide (77.6% of survivors to stage 2) with no significant differences from the control (74.3%). Lower concentrations of copper hydroxide resulted in high egg mortality whereas potassium sorbate and magnesium chloride were ineffective to avoid fungal growth and total egg mortality took place. From the obtained results, copper hydroxide baths at 200 ppm could be considered as a good alternative to formaldehyde.

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.