![]() ![]() ![]() One annulus (circuli under red line) indicates one winter season. The groups of circuli that are spaced close together are the annuli. the scale focus (F), ocean entry (OE), the annulus (A) at the end of the annual ring and the scale margin (M). When body and scale growth are resumed in the spring the first circuli. Our results, therefore, can help to elucidate the origin and spread of exotic invasive salmonids in Chile, and address one of the biggest threats to native freshwater fishes in Patagonia and other temperate zones of the Southern Hemisphere. Circuli are the fine dark lines (thin arrows). These breaks are the year marks or annuli by which age is determined. Stable isotopes analysis classified 94% of juvenile Atlantic salmon and rainbow trout to their correct farm or free-living groups. Scale growth slopes during the first year in freshwater were significantly higher in farmed than in wild-caught rainbow trout, indicating faster somatic growth under hatchery conditions. Juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) from aquaculture facilities were significantly more enriched in ä15N and lipid-corrected ä13C than river-caught individuals. We tested the ability of stable isotope analysis (SIA) and analysis of scale growth profiles to discriminate between farmed and free-living salmonids sampled around the Island of Chiloé. Ages were assigned to each fish by the author and, independently, by an assistant. The annulus here was taken to be the outermost ofthese circuli. In the first year all circuli are closely spaced. distinguish between cycloid and ctenoid scales. circuli were considered to be false annuli and were ignored in assigning age. There is therefore a need to reliably distinguish between naturally reproducing and fugitive salmonids associated with the Chilean salmonid farming industry, the second largest in the world. label correctly a diagram of a fish scale showing the focus, circuli, and annuli. In Chilean Patagonia relatively pristine aquatic environments are being modified by the introduction of exotic salmonids, initially through their deliberate release for sport fishing since the early 20th century, and more recently via the accidental escape from fish farms. ![]()
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