Fresh vs Preserved Specimens: Length-Weight Relationships of Fishes from the Western Amazon (Napo Basin, Ecuador)

Abstract:

Length-weight relationship (LWR) studies have increased in the recent years, being important for fish taxonomical analysis, ecological assessments, management and conservation practices. Although LWR studies use measurements of fresh and preserved specimens, few studies have analyzed differences between these treatments. This study analyzed the effect of preservation in LWR of 10 small-sized freshwater fish species from the Curaray River Basin (Napo Basin), eastern Ecuador. Wild caught specimens were measured, weighted, fixed in formalin, and finally preserved in 70% ethanol. Specimens from the same species batch were measured again after preservation. LWR curves were estimated from linear regressions and we compared slopes and intercepts between fresh and preserved specimens. Our results suggest that the preservation process altered weight significantly for all 10 species, while altering both weight and length for two species. The magnitude of change varied according to the morphology and maximum size of each of the evaluated species. Smaller individuals exhibited greater weight losses. The LWR estimation for 8 species are new to science. These results present new evidence of the preservation effects in LWR studies as well as a compilation of the varying results reported in the literature. We conclude that measurements on fresh specimens should be encouraged for LWR studies. However, recognizing that this is not always feasible, studies using preserved specimens should consider the effects of preservation on body length and weight.

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