Reproductive ecology of coypu (Myocastor coypus Molina, 1782) in the Middle Delta of the Paraná River, Argentina.

The objective of this study was to estimate and compare some important reproductive parameters of Myocastor coypus over time (June 2006-May 2008), in wetlands of the Middle Delta of the Paraná River (MD) Entre Ríos province, R. Argentina. Within the original coypu distribution range, the MD is among the areas of highest habitat suitability for the species. Coypus were captured and the following reproductive parameters were estimated on a monthly, seasonal and annual basis: pregnancy rate (PR), litter size (LS), gross productivity (GP) and annual production (AP). Statistical non-parametric tests were used for comparisons. Additionally, the expected birth date of each embryo and fetus was estimated by assigning it to a developmental stage category and considering the gestation period of the species. All the parameters showed high values and PR and LS differed significantly between the dry (2006) and humid years (2007). Two peaks of birth were detected, one in spring and another one in mid-autumn. The implications of these results for ensuring the sustainable management of this rodent are discussed.

Immobilization of coypus (Myocastor coypus) with ketamine hydrochloride and xylazine hydrochloride.

A combination of 100 mg/ml of ketamine hydrochloride (Ket) and 20 mg/ml of xylazine hydrochloride (Xyl) was used to immobilize coypus (Myocastor coypus). Eight mature coypus (four males and four females) were injected intramuscularly with doses ranging from 2.33 to 6.25 mg/kg of KET and 0.25 to 0.86 mg/kg of Xyl. The mean (+/- SE) time for induction, arousal, and recovery were 7.3 +/- 2 min, 23.5 +/- 0.3 min and 46 +/- 2.5 min, respectively. The mean +/- SE doses injected were 4.07 +/- 0.52 mg/kg Ket (range, 2.33 to 6.25 mg/kg) and 0.5 +/- 0.08 mg/kg Xyl (range, 0.25 to 0.86 mg/kg). No adverse responses were observed in any of the animals treated.