![]() ![]() This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: This work was funded by grants from Ministerio de Ciencia y Tecnología (CGL2007-60572 and CGL2010-14964), and Fondos FEDER (PGIDIT03PXIC30102PN Grupos de Referencia Competitiva, 2010/80). Received: SeptemAccepted: MaPublished: April 16, 2013Ĭopyright: © 2013 Marco-Rius et al. Our study highlights the profound effects that early growth can have on age at migration of a paradigmatic fish migrant and illustrates how the analysis of inter-circuli spacing can be used to reconstruct the detailed growth of individuals when these cannot be marked or are only caught once.Ĭitation: Marco-Rius F, Caballero P, Morán P, Garcia de Leaniz C (2013) Mixed-Effects Modelling of Scale Growth Profiles Predicts the Occurrence of Early and Late Fish Migrants. Early migrants grew faster than late migrants during their first year of life in freshwater in two natural populations, suggesting that migration into the sea was triggered by ontogenetic (intrinsic) drivers, rather than by competition with conspecifics. Here we show how mixed-effects modelling of scale growth increments (inter-circuli spacing) can be used to reconstruct the growth trajectories of sea trout ( Salmo trutta) and correctly classify 89% of individuals into early or late seaward migrants (smolts). The analysis of consecutive growth rings (circuli) found on scales and other hard structures offers an alternative to mark and recapture for examining individual growth variation in fish and other aquatic vertebrates where growth rings can be visualized, but accounting for autocorrelations and seasonal growth stanzas has proved challenging. ![]() Unfortunately, assessing individual variation in growth rates is problematic under natural conditions because subjects typically need to be marked, repeated measurements of body size are difficult to obtain in the field, and recaptures may be limited to a few time events which will generally vary among individuals. The most frequently used bones are otoliths, which are bones from the inner ear of fish used for balance and orientation, and operculae, which are the bony plates of the gill covers of fish.Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth variation can be interpreted in relation to conspecifics' performance. Scales are the most widely used because they are easy to collect and store.įor some fish species, scales are difficult to age, and other fish species have no scales at all, so bones from the fish must be used instead. These annuli can be counted to determine the age of the fish. In general, the growth rate of fish slows down each winter, resulting in smaller gaps between the growth rings, which bunch closer together to produce thick marks called annuli, in much the same way as the rings of a tree trunk. These growth rings are called circuli, and the gaps between them can be measured under magnification to determine growth rate. Fish scales and bones grow bigger as the fish gets older, with new layers of growth deposited around the scale each year.
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