Twice-annually spawning rainbow trout females in a cultured population from southern Chile. I. Biometric performance and reproductive cycle dynamic

Abstract

Two rainbow trout female populations (Wt-01 y Wt-02) were studied, which a percentage of individuals displayed a double annually reproductive cycle (DARC). This trait is characterized by an autumn spawning (normal reproductive cycle) and an additional one at spring (additional reproductive cycle). During seasons 2004 and 2005, the specimens that registered an additional spawning besides the normal, included 14.4% (Wt-01) and 36.2% (Wt-02) of the population. These females belong to double-cycler specimens, while those who spawn once a year are mono-cyclers. In both populations, the reproductive performance of normal reproductive cycle was comparatively evaluated in relation to the additional reproductive cycle, using seven biometricreproductive variables. The average weight of the spawning females (Wt-01: 1139 ± 116 g vs 1528 ± 105 g; Wt-02: 1195 ± 217 vs 1512 ± 176), the total fecundity (Wt-01: 2.310 ± 214 vs 3388 ± 299; Wt-02: 2.691 ± 600 vs 3.680 ± 509) and the relative fecundity ( Wt-01: 2.051 ± 278 vs 2.226 ± 299; Wt-02: 2271 ± 420 vs 2461 ± 354), exhibited significant differences in favour of the additional reproductive cycle (p < 0.05). Nevertheless, the eggs diameter (Wt- 01: 5.03 ± 0.09 mm vs. 4.70 ± 0.18 mm; Wt-02 : 4.89 ± 0.16 mm vs 4.58 ± 0.23 mm), the fertility rate (Wt-01: 86.6 ± 15.0 vs. 80.8 ± 11.9; Wt-02: 94.5 ± 7.5 vs 77.8 ± 24.9) and the eyed eggs stage survival rate (Wt-01: 83.89 % ± 7.70 vs 77.62 % ± 9.45; Wt-02: 84.73 % ± 11.80 vs 68.84 % ± 15.95), were significantly higher in the normal reproductive cycle. The quality of the eggs obtained during the additional cycle, was acceptable and compatible with it productive utilization. Analysis of additional reproductive cycle length (RCLa), the period time from autumn spawning date to spring spawning date, increases according to the spring spawning season progresses. First spawning females Wt-01 and Wt-02 had a RCLa average of 134 days (30/09/04) and 149 days (14/10/05) respectively, while the last spawners had a RCLa average of 187 days (29/11/04) and 217 days (03/02/06), respectively. In the same way, an eggs diameter increment was observed in relation with the spawning date progress during the additional reproductive cycle in Wt-01 as well as in Wt-02, showing high correlation values (r = 0,973 y r = 0,850, respectively). Additionally, the normal reproductive cycle length (RCLn) studied in a third population (Wt-03), shows a decrease tendency in relation to the progresses of the date of spawning in previous spring spawning. The RCL dynamic of normal and additional reproductive cycles in double-cycler females could be associated to an energetic compensation that supports the high cost for a female to ovulate twice in a year. A greater dispersion or asynchrony is observed in the spawning date distribution over the additional cycle in regard to the normal cycle, which could be a consequence of the heterogeneity observed in RLC.