Seasonal changes in reproductive endpoints in Trichomycterus areolatus (Siluriformes: Trichomycteridae) and Percilia gillissi (Perciformes, Perciliidae), and the consequences for environmental monitoring

As protection of the natural reproductive pattern is necessary to ensure adequate conservation of natural populations, we examined some typical reproductive endpoints throughout a reproductive season in two Chilean species that lack this baseline information. Trichomycterus areolatus and Percilia gillissi both have maximum gonad development for an austral spring spawning period beginning in October/November. Trichomycterus areolatus appears to spawn many times, as there was no significant correlation between gonad size and body size, a characteristic of asynchronous spawners. Percilia gillissi appears to be a multiple spawner, with larger individuals spawning into January, although most fish completed spawning by December. To design a study for monitoring purposes with these species, the best sampling periods would be late fall (June) and spring (October) for P. gillissi, as power analysis indicated a target sample size of 20 females in June and 34 in October; the sample size in October could be reduced to 12 by selecting females > 50 mm in length, thereby reducing the variability. Trichomycterus areolatus gonadal variability was much higher, requiring a sample size in excess of 80 individuals for adequate statistical power. An understanding of these basic reproductive and metabolic patterns in South American freshwater fishes will help ensure better management of the water resources.