Crystalline otoliths in teleosts: Comparisons between hatchery and wild coho salmon (Oncorhynchus kisutch) in the Strait of Georgia

Abstract

page 361 Introduction 361 Material and methods 364 Results 364 Discussion 366 References 368Abstract Otoliths, or 'ear stones', are calcium carbonate structures found in all vertebrates. In teleosts, they have a number of sensory functions, including hearing. Daily growth increments of these structures have permitted advanced age and population studies of teleosts. Whereas 'normal' otoliths are composed of crystals imbedded within a protein matrix as aragonite, a 'crystalline' form of calcium carbonate termed vaterite is also found. A review of the otolith literature demonstrates a significant level of understanding of the structure and function of otoliths, but the cause for crystalline otolith structure remains speculative. Pairs of otoliths from hatchery and wild juvenile and adult coho salmon (Oncorhynchus kisutch) were examined visually for determination of otolith microstructure type. The vateritic or crystalline otoliths were found in much higher percentages in juvenile hatchery-reared coho salmon than in juvenile wild coho salmon, supporting previous studies. There did not seem to be any negative impact on size or survival. There was also no correlation between crystalline otoliths and premature maturation in coho males. A preliminary study of adult coho salmon returning to Big Qualicum and Chilliwack hatcheries showed even higher ratios of vateritic otoliths than observed in juveniles.

Rapid growth causes abnormal vaterite formation in farmed fish otoliths

“…Sweeting et al (2004) hypothesised that metabolic rate may influence vaterite formation. They also examined premature maturation ('jacking') in salmon, expecting that the increased metabolic rate would increase vaterite prevalence, but they found no evidence to support this.…”

“…Both otoliths were removed from Atlantic salmon from each experiment, cleaned, dried, and photographed under a dissecting microscope at 10× magnification. As vateritic otoliths from Atlantic salmon are easy to distinguish visually from aragonitic ones (Sweeting et al, 2004;Oxman et al, 2007;Reimer et al, 2016), they were visually scored as 'vaterite' if any vaterite crystals were visible (indicating that the switch to vaterite formation had been made), or 'aragonite' if they were not. Vaterite prevalence was defined as the proportion of vaterite otoliths in each replicate tank.…”

“…Previous attempts to induce vaterite formation by temporarily exposing juvenile fish to different temperatures for short periods of time were unsuccessful (Gauldie, 1996), and there is no correlation between vaterite prevalence and fish sex or early maturation rates (Sweeting et al, 2004), or the prevalence of other skeletal deformities (Tomás and Geffen, 2003). The recent discovery of marked differences in prevalence between wild and farm-reared fish suggests that the cause(s) of vaterite formation is a consistent difference between these two groups or the environments they experience (Reimer et al, 2016).…”

“…Third, hatcheries often use continuous light to enhance growth and suitability for sea-cage transfer (Saunders et al, 1985), which can affect physiology and development (Oppedal et al, 2003). Finally, temperature fluctuations within hatcheries may influence vaterite formation (Sweeting et al, 2004), which may be particularly important in early life (Wargelius et al, 2005). As otolith formation is a complex interaction between genetic and environmental factors (Radtke and Shafer, 1992), it is important to evaluate the separate and interacting effects of all possible factors.…”

Morphological and biochemical analyses of otoliths of the ice‐fish Chionodraco hamatus confirm a common origin with red‐blooded species

“…A vateritic asteriscus is frequent in several teleosts (Lowenstam & Weiner, 1989;Campana, 1999;Falini et al 2005;Lenaz et al 2006), whereas a vateritic sagitta is characteristic of ancient species such as Ciclostomata, Polypterus and sturgeons (Carlstrom, 1963). It is, however, occasionally present as an abnormality (Gauldie, 1986;Ma et al 2007) or in juvenile (Tomàs et al 2004;Sweeting et al 2004) samples. Its constitutive presence in adults of a modern Notothenioid cannot be related to external factors such as stress or infections (Iguchi et al, 2003).…”