Reproductive performance assessed during three spawning seasons in a naturalized rainbow trout population from southern Chile

Abstract

Naturalized rainbow trout (Oncorhynchus mykiss) populations are an important recreational fishing resource in the Araucanian lakes of southern Chile, but few reproductive studies have been undertaken to assess their sustainability. It is important to address this issue, since this analysis may provide information for improving management activities. In this study we carried out a biometric and reproductive analysis of naturalized rainbow trout breeders to describe their performance and to explore the variables that could determine fecundity, fertilization in addition to egg survival and size. We collected naturalized rainbow trout breeders from six tributaries of Calafquén Lake, during 2006, 2007 and 2012 to record their biometric and reproductive traits. Spawning and incubation were performed under controlled conditions in a hatchery facility to improve the recording process. In each spawning season, total fecundity (TF, No. of eggs/female), relative fecundity (RF, No. of eggs/kg female), fertilization rate (FR, %), egg diameter (ED, mm) and eyed egg survival (EES, %) were modeled as a function of biometric and reproductive parameters, using general linear mixed models. We used this statistical tool to explore the relationships between these reproductive traits and other breeder traits in order to identify all the potential combinations that could be linked to TF, RF, FR, ED and EES. The spawning period ranged from September to November (i.e., spring spawning season), with a clear spawning peak in October in all reproductive seasons. Mean TF (from 2275.9 to 3438.7) and RF (from 1730.5 to 1909.8) fell within the range of, or were close to, data reported for other Araucanian lakes, respectively. Mean values of FR and EES were relatively high, ranging from 88.8% to 93.3% and between 83.4% and 88.8%, respectively. Models indicated that TF is significantly affected by the interaction between female body weight and egg weight, while RF is affected by the combination of female body length and egg weight. In addition, a positive correlation was observed between female body weight and total fecundity, while an inverse association was recorded between relative fecundity and female body length. This trend is in accordance with the trade-off pattern between egg number and fish size described for naturalized populations of rainbow trout from the Northern Hemisphere. However, regression equations output suggests that the reproductive performance of the Calafquén Lake population has a more depleted fecundity in comparison either with naturalized populations from the Northern Hemisphere, or with cultured stocks of this species. Models for ED revealed that this variable is affected by egg weight and also by body length or body weight, all with positive correlations. This result concurs with observations reported for other naturalized populations of rainbow trout from North America, further supporting evidence that larger females of this species produce larger eggs than smaller females. Models for EES revealed the significant positive effect of fertilization rate and relative fecundity, being the latter an unexpected result, given that insignificant correlations between these variables have been found in cultured stocks of this species. Overall, the population analyzed exhibited a regular spawning period, and an optimal reproductive performance in terms of egg survival. To promote the sustainability of the naturalized rainbow trout of Calafquén Lake, we recommend the use of hatchery propagation of wild adults to support the production of fry to be used in subsequent restocking activities. This management effort can benefit because the broodstocks have a short spawning period during their spring run.