Effects of different shelters on the growth and survival of juveniles of the freshwater crayfish Cherax quadricarinatus under laboratory conditions.

VIAU, V.E.; RODRÍGUEZ, E.M.

Veracruz

Congreso; World Aquaculture 2009; 2009

World Aquaculture Society

Survival (%) and body weight at the end of the one month assay with early (dashed bars) or advanced (empty bars) juveniles. Vertical lines: standard errors. Different letters indicate significant differences (p<0.05). 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 Pipes Net Tower a a,b   b 0 20 40 60 80 100 Pipes Net Tower      The current study was aimed at evaluating the effect of different shelter designs on both survival and growth of juveniles of the Australian freshwater crayfish C. quadricarinatus (Decapoda, Parastacidae), in order to further improve their production in farmers. Two size classes of juveniles were employed, named as early (0.02 g of body weight at the beginning of the assay), or advanced (near 1 g). These sizes correspond, respectively, to the hatchery and nursery steps in farmers. Ten to twelve juveniles were placed in glass aquaria (900 cm2 of bottom surface), therefore maintaining the optimum density previously proposed by several authors. Dechlorinated tap water (80 mg/L of water hardness, as CaCO3 equivalents, pH: 7.5) was continuously aerated in each aquarium. Temperature was maintained in 25 ± 2 °C and photoperiod was held at 14:10 (L:O) throughout. Two times a week, a total replacement of water was made in all aquaria. Animals were daily fed ad libitum with commercial pellets (Tetra Diskus®). Three types of refuges were assayed, by assigning four aquaria to each of the following experimental groups: a) PVC pipes (1.5 and 2.5 cm diameter for early and advanced juveniles respectively) added in excess and placed horizontally and separately at the bottom of the aquarium, b) Forty PVC pipes joined vertically (5 rows of 8 pipes) conforming a tower, that was also covered by a plastic mesh (pore size: 1.5 cm and 3 cm for early and advanced juveniles respectively), and c) Plastic net, forming by a compact plastic cloth placed following a rose-shaped design inside a cylinder (12 cm diameter) of plastic mesh (same pore sizes as mentioned above). Both survival and body weight (measured at a precision of 0.1 mg) of juveniles at the end of the one month assay are shown in the Figures. No significant differences (p>0.05) were observed in body weight, in any case. However, a significant (p<0.05) higher survival was observed for early juveniles maintained in the tower design, when compared to the isolated pipes design, while the plastic net caused an intermediate effect. This results shows that survival of early juveniles of C. quadricarinatus could be greatly improved by only adopting a vertical (tower) shelter design, probably by optimizing the space utilization and therefore reducing the competence among juveniles.