Rapid growth causes abnormal vaterite formation in farmed fish otoliths


Sagittal otoliths are essential components of the sensory organs that enable all teleost fish to hear and maintain balance, and are primarily composed of calcium carbonate. A deformity, where aragonite (the normal crystal form) is replaced with vaterite, was first noted over 50 years ago but its underlying cause is unresolved. We evaluated the prevalence of vateritic otoliths from two captive rearing studies which suggested that fast growth, due to environmental rather than genetic control, led to vaterite development. We then tested this by varying light and temperature to create phenotypes with different growth rates, which resulted in fast growers (5x larger) having 3 times more vaterite than slow growers. A decrease in either the ratio of otolith matrix proteins (otolin-1/OMM-64) or [Ca(2+)]/[CO3(2-)] may explain why fast growth causes vaterite deposition. As vaterite decreases hearing sensitivity, reducing growth rates in hatcheries may improve the welfare of farmed fish and increase the success of conservation efforts.
© 2017. Published by The Company of Biologists Ltd.
Rapid growth causes abnormal vaterite formation in farmed fish otoliths
Reimer, T.a, Dempster T.a, Wargelius, A.b, Fjelldal, P. G.c, Hansen, T.c, Glover,,
Solberg, M.F.d, Swearer, S. E.a
aSchool of BioSciences, University of Melbourne, Victoria 3010, Australia
b Section of Molecular Biology, Institute of Marine Research (IMR), Bergen, Norway
c Institute of Marine Research (IMR), Matre Research Station, 5984 Matredal, Norway
d Population Genetics Research Group, Institute of Marine Research (IMR), Bergen, Norway
e Sea Lice Research Centre, Department of Biology, University of Bergen, Norway
Correspondence to
Journal of Experimental Biology • Advance article the most recent version at
J Exp Biol Advance Online Articles. First posted online on 8 June 2017 as doi:10.1242/jeb.148056
Sagittal otoliths are essential components of the sensory organs that enable all teleost fish to
hear and maintain balance, and are primarily composed of calcium carbonate. A deformity,
where aragonite (the normal crystal form) is replaced with vaterite, was first noted over 50
years ago but its underlying cause is unresolved. We evaluated the prevalence of vateritic
otoliths from two captive rearing studies which suggested that fast growth, due to
environmental rather than genetic control, led to vaterite development. We then tested this by
varying light and temperature to create phenotypes with different growth rates, which resulted
in fast growers (5x larger) having 3 times more vaterite than slow growers. A decrease in either
the ratio of otolith matrix proteins (otolin-1/OMM-64) or [Ca2+]/[CO32-] may explain why fast
growth causes vaterite deposition. As vaterite decreases hearing sensitivity, reducing growth
rates in hatcheries may improve the welfare of farmed fish and increase the success of
conservation efforts.
Journal of Experimental Biology • Advance article
The bony structures of the inner ear of vertebrates aid hearing and balance, with deformities in
these structures typically causing sensory impairment (Merchant and Nadol, 2010). In teleost
fish, the most abundant and diverse vertebrate group, the sagittal otolith is a primary part of the
hearing organ and is composed of calcium carbonate in the crystal form aragonite (Carlström,
1963). A deformity, where the aragonite is replaced by vaterite crystals, is abnormal in the
wild, occurring in 1-24% of otoliths. However, it is extremely common in farmed fish, with its
prevalence being on average 3.7 times higher in farmed fish than their wild counterparts and,
in the most recent study, affecting 100% of harvest-size farmed Norwegian salmon (Reimer et
al., 2016). Vaterite formation is irreversible once begun, and vaterite replacement results in
otoliths which are larger, lighter, more brittle, and less regularly-shaped than their aragonite
counterparts. Due to these difference, replacement of aragonite by vaterite likely causes severe
hearing loss by reducing otolith function, potentially impacting fish welfare and restocking
efficiency (Reimer et al., 2016).
Despite over 50 years of evidence of vateritic otoliths (Palmork et al., 1963; Mugiya, 1972;
Strong et al., 1986; Bowen II et al., 1999), the cause(s) of their formation are unknown.
Previous attempts to induce vaterite 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 gender 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 are consistent differences between these two groups or the environments
they experience (Reimer et al., 2016).
There are several factors that differ in universal ways between farmed and wild settings which
may be affecting otolith development. First, due to domestication, farmed fish, such as Atlantic
salmon (Salmo salar L.) now display a range of genetic differences to wild conspecifics
(Glover et al., 2017), so genetic predisposition to vaterite deformation is possible. While
vaterite prevalence in wild-origin fish raised in captivity is high (Fig. 6, Gauldie, 1996), its
heritability has not been explicitly tested. Second, the composition of wild and commercial
feeds differs, especially in the proportions of terrestrially-sourced nutrients important for
proper development (Naylor et al., 2009). Third, hatcheries often use continuous light to
enhance growth and suitability for sea-cage transfer (Saunders et al., 1985), which can affect
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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.
Determining the cause of the vaterite otolith deformity in cultured fish has broad significance
to aquaculture and conservation. As >50% of farmed fish have ~50% loss in hearing sensitivity
due to vaterite (Reimer et al., 2016), pinpointing the cause of this deformity could drive
measures to improve the welfare of billions of farmed fish worldwide. Furthermore, over 100
countries release hatchery-raised fish for restocking wild fisheries (sea ranching or supportive
breeding). Reducing the incidence of vaterite could increase the generally poor success rates
of these activities (Moore et al., 2012).
Here, we conducted three experiments to determine if the separate and interacting effects of
diet, rearing temperature, light regime and genetic origin might be influencing vaterite
prevalence in hatchery-reared fish. As the two initial experiments suggested a relationship
between fish size (i.e. growth rate) and vaterite formation, we conducted a final experiment to
isolate and test the effect of growth rate on vaterite prevalence.
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Materials and Methods
All experiments were conducted at the Institute of Marine Research field research station in
Matre, Norway (60°N). Both otoliths were removed from fish from each experiment, cleaned,
dried, and photographed under a dissecting microscope at 10x 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.
Experiment 1 Effects of genetic origin and diet on vaterite prevalence
Salmon eggs (wild-caught broodstock, commercial strain A, and their F1 hybrids) were reared
together in ~6°C/complete darkness, and hatched in January, 2014 (see Harvey et al., 2016 for
experiment details). In March, 2700 fry were transferred to 6 freshwater tanks (450 fry per
tank, n = 2 tanks per diet treatment).
Fry were fed to satiation with either a commercial diet (NutraXP, Skretting UK), a
carbohydrate-rich diet (Coarse Fish 23, Skretting UK), or a “natural” diet mimicking the food
available within spring spawning rivers: a mix of insect larvaes; black mosquito larvae
Culicidae and glassworms, i.e., transparent larvae of the phantom midge
Chaoboridae Chaoborus, as well as freshwater copepods Cyclopidae Cyclops and water fleas
Daphniidae Daphnia (Ruto Frozen Fishfood).
At ~130 days post-feeding (dpf), all fish were euthanised, weighed, measured for fork length
and weight, and DNA tested using parentage analysis to identify genetic origin. Otoliths were
extracted from 45 fish per replicate tank (15 individuals per genetic origin, randomly selected
after their genetic origin had been identified). Final replicate numbers were n = 2 for each
genetic origin/diet treatment combination (n = 270 fish assessed in total). Results were analysed
with a 2-way ANOVA (diet and genetic origin as fixed factors, as well as their interaction
term). Post-hoc Tukey HSD tests assessed differences between individual treatments.
Experiment 2 Effects of temperature shock and light regime on vaterite prevalence
Salmon eggs (commercial strain B) were reared in 6°C/complete darkness, and hatched in
January, 2012 (see Wargelius et al., 2005 for experiment details). Heat-shock treatments
exposed alevins to 12°C for 24 hours at 20 degree-days (20dC), 220 degree-days (220dC), or
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no heat-shock (control). In March, fry were transferred to 18 freshwater tanks (~295 fry per
tank, n = 3 tanks per treatment).
Nine tanks, three for each heat shock treatment, were exposed to standard hatchery conditions
of continuous light (LL), and an additional nine tanks were exposed to 12 hours of light and 12
hours of dark per day (LD), mimicking average spring conditions.
At ~285 dpf, 40 fish from each replicate were euthanised. Some groups were too degraded for
otolith extraction. Final replicate numbers were: n = 3 for LD/control, LL/control and
LD/220dC; n = 2 for LD/20dC and LL/20dC; and n = 1 for LL/220dC (n = 560 fish assessed
in total). As there was only one replicate tank for the LL/220dC treatment, results were
analysed using a 2-way ANOVA (light regime and heat shock as fixed factors, without the
interaction term). As maturation, which affects growth, differed between light-regime
treatments a 1-way ANOVA (maturity by light regime treatment as a fixed factor) and post-
hoc Tukey HSD test were performed to assess the effect of maturation on the observed response
to the light regime treatment.
Experiment 3 Effects of temperature and light regime (growth rate) on vaterite prevalence
Salmon eggs (commercial strain B) were incubated at ~6°C/complete darkness, and hatched in
January, 2015. In March, 2700 fry were transferred to 12 freshwater tanks (225 fry per tank, n
= 3 tanks per treatment).
Light treatments consisted of the hatchery standard of continuous light (LL) or 18 hours of
light and 6 hours of darkness per day (LD), which was designed to reduce growth rate without
inducing maturity. Light treatments were combined with either High (13°C) or Low (6°C)
temperatures to create four treatment groups (LL-HighT; LL-LowT; LD-HighT; LD-LowT).
At 155 dpf, 40 fish from each tank were euthanised, weighed, and their otoliths extracted. Final
replicate numbers were n = 3 tanks for each light/temperature treatment (n = 480 fish assessed
in total). Results were analysed using a 2-way ANOVA (light and temperature as fixed factors),
and post-hoc Tukey HSD tests assessed differences between treatment groups. Based on the
results of Experiments 1 and 3, a linear regression was used to test if vaterite prevalence was
related to average fish growth rate (final weight divided by dpf).
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Experiment 1 Effects of genetic origin and diet on vaterite prevalence
Commercially-fed fish were 2-3 times more likely to have vaterite otoliths than those fed
natural or carbohydrate-rich diets. Vaterite prevalence varied with the interaction between
genetic origin and diet (F4,9 = 5.3, p = 0.018), thus the effect of diet upon vaterite prevalence
differed between the farmed, hybrid and wild salmon (Fig.1 A). There was no main effect of
genetic origin (F2,9 = 0.03, p = 0.98), and vaterite prevalence was more common in fish fed a
commercial diet than those fed a natural or carbohydrate diet (F2,9 = 49.2, p < 0.001). Pairwise
comparisons showed that the higher vaterite prevalence in individuals fed a commercial diet
compared to the alternative diets was only significant for farmed and hybrid fish.
Experiment 2 Effects of temperature shock and light regime on vaterite prevalence
Vaterite prevalence was only affected by photoperiod (lighting: F1,9 = 5.4, p = 0.04; heat-shock:
F2,9 = 0.61, p = 0.56). Vaterite prevalence was overall 15% higher in the LL compared to the
LD treatment. However, 72% of males within the LD treatment became sexually mature. The
lower vaterite prevalence in the LD treatment was due to the maturation of males (maturation:
F2,14 = 6.9, p = 0.008). Vaterite prevalence in LD mature males was 15% lower than in LD
immature fish, and 26% lower than in the LL group, which were all immature (Fig. 1B).
Experiment 3 Effects of temperature and light regime (growth rate) on vaterite prevalence
Vaterite otoliths were 3 times more prevalent in the fastest-growing fish compared to the
slowest (Fig. 1C). Mean fish length and weight varied depending on both light and temperature
treatments (light × temperature interaction: length F1,8 = 39, p < 0.001, weight F1,8 = 63, p <
0.001). Lengths and weights differed between temperature treatments but were greatest in the
LL (HighT: 16.0 ± 0.2 cm, 60 ± 1.8 g; LowT: 5.1 ± 0.06 cm, 1.5 ± 0.03 g) versus LD (HighT:
14.8 ± 0.2 cm, 46 ± 0.3 g, LowT: 5.1 ± 0.06 cm, 1.5 ± 0.03 g) treatments (p < 0.05 in all cases).
Vaterite prevalence varied depending on the interaction between lighting and temperature, and
temperature alone; there was no main effect of lighting (light × temperature interaction: F1,8 =
11, p = 0.011, temperature: F1,8 = 992, p < 0.001; lighting: F1,8 = 0.6, p = 0.45). Post-hoc
pairwise comparisons showed that vaterite prevalence in the HighT treatment was 63% higher
than the LowT treatment in the LL treatment, but only 51% higher in the LD treatment (Fig.
Journal of Experimental Biology • Advance article
Vaterite prevalence increased with growth rate in Experiments 1 and 3 (Fig. 2, R2 = 0.89, p <
Despite long-standing awareness of the occurrence of abnormal vaterite replacement in sagittal
otoliths, few studies have investigated why vaterite forms. By rearing fish of wild, hybrid and
domesticated origin, and manipulating diet and the rearing environment, we show that fast-
growing fish are 3 times more likely to have vateritic otoliths than slow-growing fish (Fig. 2),
providing the first compelling evidence that abnormally fast growth is likely the universal
underlying cause. By optimising conditions to maximise growth rates, we successfully induced
vaterite in 90% of otoliths.
Vaterite incidence in the slowest-growing fish (29%) was not as low as in wild populations
(13%; Reimer et al. 2016), which could indicate either that there are multiple causes of vaterite
formation, fish with vateritic otoliths have higher mortality rates in the wild, or that sub-optimal
hatchery conditions still produce, on average, faster-growing fish than wild conditions.
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.
They used a coarser method of vaterite classification (a scale of 1-4 based on vaterite area) and
measured prevalence at the organism level rather than as the percentage of affected otoliths, so
it is possible that their sample size was not large enough to detect the effect. To date, vaterite
prevalence with respect to maturation has only been investigated in males. A similar
investigation into females may further clarify the connection between growth rate, maturation,
and vaterite prevalence.
How fast growth leads to abnormal vaterite formation is unclear, although once normal
aragonite deposition is disrupted, vaterite formation appears permanent. There are two possible
mechanisms leading to disruption of aragonite:
(1) The organic matrix is a protein aggregate lattice whose composition influences the
crystal polymorph (Mann, 2001; Falini et al., 2005), and aragonite is only deposited
when all components are present. Fast growth might change the composition of otolith
matrix proteins in a way that favours deposition of vaterite over aragonite. Using in
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vitro crystallization experiments, Tohse et al. (2009) found that otolith matrix
macromolecule- 64 (OMM-64) favours the formation of vaterite, whereas the presence
of OMM-64 in combination with otolin-1 favours the formation of aragonite. If fast
growth results in a decrease in the otolin-1/OMM-64 ratio within the protein aggregate,
this could cause the switch to abnormal vaterite otoliths.
(2) A high [Ca2+]/[CO32-] ratio in the endolymph promotes aragonite formation over other
calcium carbonate polymorphs (Chen and Xiang, 2009). Inorganic carbon (HCO3) is
transported to the endolymph across the saccular membrane by energy-dependent
mechanisms involving HCO3-ATPase and Cl/HCO3 exchangers (Tohse and Mugiya,
2001). Presumably faster-growing fish have more energy, which may lead to a greater
rate of transport of HCO3 relative to Ca2+ into the endolymph, resulting in a lower
[Ca2+]/[CO32-] ratio and favourable conditions for vaterite formation.
Identifying which of these mechanisms contributes to faster growing fish being more likely to
have abnormal vateritic otoliths requires further research.
Our findings have potential implications for the food production industry, as well as supportive
breeding or restocking programs in the wild. Aquaculture industries promote increasing
individual growth (Thodesen and Gjedrem, 2006; Asche and Bjørndal, 2011) as it increases
feed conversion efficiency, which in turn increases sustainability and economic efficiency
(Cook et al., 2000). Rapid growth has previously been shown to increase the incidence of
cataracts (Ersdal et al., 2001), but the present study is the first to show that it permanently
deforms otoliths. If fish welfare is negatively impacted through impaired hearing (Reimer et
al., 2016), the industry could reduce growth rates to prevent abnormal vaterite formation.
Alternatively, they may need to investigate methods of reducing vaterite prevalence while
striving to maintain or increase growth rate.
Reducing vaterite prevalence may also be important for wild fish conservation and stock
enhancement, as restocking (or supportive breeding) programs rely on the survival of hatchery-
reared juveniles (Sweeting et al., 2003). Rearing environments are typically optimized to
maximize juvenile size-at-release, with the aim of reducing mortality (Cross et al., 2009).
However, despite these efforts, return rates of hatchery-reared juveniles remain low (Araki et
al., 2008; Beamish et al., 2012). As hearing loss may affect post-release survival through
compromised predator evasion (Sand and Karlsen, 2000) and navigation (Gagliano et al.,
2008), our results suggest that reducing vaterite prevalence by limiting growth rate could
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benefit fish restocking efforts. Vaterite prevalence in wild or stocked salmon returning from
sea has never been investigated, but it may reveal the relationship between early growth rate,
vaterite formation and marine survival.
This work was conducted in accordance with the laws and regulations of the Norwegian
Regulation on Animal Experimentation 1996. The protocol was approved by the Norwegian
Animal Research Authority (permits 7121 and 6546). We thank the IMR staff at Matre for
technical assistance, and Oliver Thomas for advice on otolith formation mechanisms. We also
acknowledge Eva Troianou for laboratory analyses for DNA parentage testing (INTERACT
project; Norwegian Research Council).
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Figure 1: Prevalence of vaterite otoliths between: A) genetically wild (white, n = 6 tanks),
hybrid (grey, n = 6) and farmed (black, n = 6) Atlantic salmon fed different diets (Experiment
1; n = 810 fish assessed in total); B) all immature (white, n = 5 tanks), and mature males (black,
n = 4) from all heat shock treatments combined reared under different photoperiods
(Experiment 2; n = 560 fish assessed in total); and C) fish reared under continuous light (LL,
white, n = 6 tanks) or long day (LD, grey, n = 6) at different temperatures (Experiment 3; n =
480 fish assessed in total). Bars show raw means ± SE, while letters show significant groupings
(p < 0.05) as determined by post-hoc Tukey HSD tests (which are based on pairwise
comparisons of least squares means and a pooled SE). Inset: Sagittal otoliths from a juvenile
Atlantic salmon, with scale bar = 1 mm (bottom right). The left otolith is entirely aragonite,
while the right otolith is approximately 90% vaterite by planar area.
Journal of Experimental Biology • Advance article
Figure 2: Proportion of vaterite otoliths from Experiments 1 and 3 in response to growth rate,
determined by a linear regression. Experiment 1 is divided by temperature treatment: HighT
(+, n = 6) and LowT (×, n = 6). Experiment 3 (n = 18) shows each genetic origin x diet
treatment: Farmed (black) hybrid (grey) and wild (white) origins by standard ( ) carbohydrate
( ) and natural diets ( ).
Journal of Experimental Biology • Advance article
... The sagitta, the largest otholith, is usually composed of calcium carbonate crystals in the form of aragonite. A deformity, extremely common in farmed fish, where the aragonite is replaced by vaterite (a clearer crystallised form of the calcium carbonate), heavily affects the farmed salmon [14]. ...
... Sagittal otoliths are essential components of the sensory organs that are composed of calcium carbonate. In abnormal otoliths, aragonite (the normal crystal form) is replaced with vaterite that decreases hearing sensitivity, reducing growth rates [14]. In some Chinook salmon studies vateritic sagittae were bigger and less dense than the aragonitic form, and vaterite presence was associated with moderately altered saccular epithelia and a significant decrease in auditory sensitivity [24]. ...
... After assessment (in our samples the otolith proportion that was affected by vaterite in control cages was higher than in exposed cages) we concluded that differences of the vaterite presence in otoliths had no relation with sound exposure, but was probably explained by a deficiency in nutrition associated to captivity as has been shown in previous studies [14]. ...
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The use of bioacoustic methods to address sea lice infestation in salmonid farming is a promising innovative method but implies an exposure to sound that could affect the fish. An assessment of the effects of these techniques related to the salmon’s welfare is presented here. The fish were repeatedly exposed to 350 Hz and 500 Hz tones in three- to four-hour exposure sessions, reaching received sound pressure levels of 140 to 150 dB re 1 µPa2, with the goal of reaching total sound exposure levels above 190 dB re 1 µPa2 s. Gross pathology and histopathological analysis performed on exposed salmons’ organs did not reveal any lesions that could be associated to sound exposure. The analysis of their otoliths through electron microscopy imaging confirmed that the sound dose that was used to impair the lice had no effects on the fish auditory organs.
... The functional mechanisms underlying vaterite deposition and its consequences are largely unknown; hormonal (5), genetic, or biochemical (1) factors have been hypothesised as predictors, and there is growing evidence of the roles of different proteins in polymorph deposition at the molecular level (10). Vaterite prevalence during conventional hatchery rearing is reportedly associated with stress related to stocking density and handling practises (4), and with the typically faster growth rates mediated by diet, longer photoperiods that allow for continuous feeding, and temperature regimes (11). Consequently, vaterite is over 10 times more common in farmed than in wild fish, as demonstrated in a review spanning several species including a range of salmonids (6). ...
... Impaired hearing may generate biased soundscape-dependent swimming behaviour and challenge the welfare of captive fish. If the presence of vaterite is high in hatchery fish reared for release into natural habitats, impaired hearing may also bias the perception of predation risk and prey presence, sensory cues that are important for survival and growth (6,9,11). ...
... However, the underlying mechanism behind vaterite replacement is still unknown. Reimer et al. (11) found vaterite to be strongly related to rapid growth rates in Atlantic salmon juveniles and suggested that abnormally fast growth disrupts normal aragonite deposition and triggers replacement by vaterite in otoliths. This is in accordance with the results of the present study, where the extent of vaterite was strongly related to body size. ...
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Sagittal otoliths are calcareous structures in the inner ear of fishes involved in hearing and balance. They are usually composed of aragonite; however, aragonite can be replaced by vaterite, a deformity which is more common in hatchery-reared than in wild fish. Vaterite growth may impair hearing and balance and affect important fitness-related behaviours such as predator avoidance. Captive rearing techniques that prevent hearing loss may have the potential to improve fish welfare and the success of restocking programmes. The aim of this study was to test the effect of structural tank enrichment on vaterite development in the otoliths of hatchery-reared juvenile Atlantic salmon Salmo salar, and to assess the effects of vaterite on immediate predation mortality and long-term survival after release into the wild. Fry were reared in a structurally enriched or in a conventional rearing environment and given otolith marks using alizarin during the egg stage to distinguish between the treatment groups. Otoliths were scrutinised for the presence and coverage of vaterite at 6, 13, and 16 weeks after start feeding, and the growth traits were measured for enriched and control fry when housed in tanks. In a subsequent field experiment, juveniles were released in the Rasdalen river (western Norway), and otoliths of enriched reared and control reared fry were scrutinised from samples collected immediately prior to release, from predator (trout Salmo trutta) stomachs 48 h after release and from recaptures from the river 2–3 months after release. Vaterite otoliths occurred as early as 6 weeks after start feeding in hatchery-reared S. salar. Vaterite occurrence and coverage increased with fish length. Enriched rearing had no direct effect on vaterite formation, but enriched reared fry grew slower than control fry. After release into the wild, fewer salmon fry with vaterite otoliths had been eaten by predators, and a higher proportion of fry with vaterite otoliths than those lacking vaterite were recaptured in the river 2–3 months after release. Contrary to expectations, this suggests that vaterite does not increase predation mortality nor reduce survival rates in the wild during the early life stages.
... Vaterite depositions can also be found in sagitta and lapillus otoliths in around 1 to 24% of wild populations, with calcite being much rarer (Hughes et al., 2004;Nehrke et al., 2012). Otoliths can start depositing CaCO 3 as aragonite and then later switch to other polymorphs such as vaterite, a change that seems to be irreversible (Reimer et al., 2017). Vaterite deposition is commonly found in a range of fishes reared under aquaculture conditions, up to 3.7 times more frequent compared to wild populations (David et al., 1994;Tomas and Geffen, 2003). ...
... Early studies ruled out the possibility of a genetic predisposition to replace aragonite by other CaCO 3 polymorphs (Gauldie, 1986), but with better genotyping and pedigree reconstruction techniques, this idea has been recently re-examined (Coll-Lladó et al., 2018) indicating genetic susceptibility to replace aragonite. In addition, Reimer et al., (2017), suggested that the probable cause of vaterite deposition in aquaculture reared animals was the high growth rates experienced under intensive aquaculture conditions. The authors suggested two possible mechanisms for how fast growth can promote vaterite deposition: 1) by modifying the otolith-1/OMM-64 proportion of the otoliths organic matrix, and/or 2) a lower [Ca +2 ]/[ | ] ratio due to a higher transport of towards the endolymph arising from high-energy availability in diets for fast-growth animals. ...
In fish otoliths, CaCO3 normally precipitates as aragonite, and more rarely as vaterite or calcite. A higher incidence of vaterite deposition in otoliths from aquaculture-reared fish has been reported and it is thought that high growth rates under farming conditions might promote its deposition. To test this hypothesis, otoliths from growth hormone (GH) transgenic coho salmon (TF) and non-transgenic (NT) fish of matching size were compared. Once morphometric parameters were normalized by animal length, we found that TF fish otoliths were smaller (-24%, -19%, -20% and -30%; P<0.001 for length, width, perimeter and area, respectively) and rounder (-12%, +13.5%, +15% and -15.5% in circularity, form factor, roundness and ellipticity; P<0.001) than otoliths from non-transgenic fish of matching size. Interestingly, transgenic fish had smaller eyes (-30% eye diameter) and showed a strong correlation between eye and otolith size. We also found that the percentage of otoliths showing vaterite deposition was significantly smaller in transgenic fish (21-28%) compared to non-transgenic (69%; P<0.001). Likewise, the area affected with vaterite deposition within individual otoliths was reduced in transgenic fish (21-26%) compared to non-transgenic (42.5%; P<0.001). Our results suggest that high growth rates per se are not sufficient to cause vaterite deposition in all cases, and that GH overexpression might have a protective role against vaterite deposition, an hypothesis that needs further investigation.
... For instance, aragonite and vaterite portions of European eel (Anguilla anguilla) otoliths have differing strontium (Sr) concentrations that are like those associated with migrations between marine and freshwater systems 13 . The frequency of otoliths comprised of multiple CaCO 3 polymorphs is poorly described at both a species and individual level, but otoliths with multiple polymorphs do not appear restricted to specific taxa or clades 10 and have been linked to environmental factors [14][15][16][17] for a fish species, it appears that any combination of CaCO 3 polymorphs is possible within an individual otolith, otolith pair, and among populations (e.g. ...
... To date, the most direct evidence for trace element partitioning between calcite, aragonite, and vaterite is from Pracheil et al. 10 who used simultaneous X-ray fluorescence and XRD to assess Chinook salmon otoliths; the assessed otolith was comprised of all three CaCO 3 polymorphs, and Sr concentrations were measurably higher in calcite regions than in vaterite but seemingly lower than aragonite (note that aragonite and calcite regions may have precipitated asynchronously and therefore changes in Sr concentration may reflect temporal changes in environmental conditions and/or mineralogy). Some experimental studies indicate fish growth rates 15 , ambient water temperature 16,34 , dissolved carbon dioxide 35 , protein expression 36 , and ontogeny 17 affect CaCO 3 polymorph expression in otoliths, but, in general, mechanistic associations between polymorph presence and environmental and genetic factors are not known. Unfortunately, due to the relatively small sample size of this study, we were unable to explore relationships between extrinsic factors, such as those shown in Table 2, and polymorph expression. ...
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Otoliths are frequently used to infer environmental conditions or fish life history events based on trace-element concentrations. However, otoliths can be comprised of any one or combination of the three most common polymorphs of calcium carbonate—aragonite, calcite, and vaterite—which can affect the ecological interpretation of otolith trace-element results. Previous studies have reported heterogeneous calcium carbonate compositions between left and right otoliths but did not provide quantitative assessments of polymorph abundances. In this study, neutron diffraction and Raman spectroscopy were used to identify and quantify mineralogical compositions of Chinook salmon Oncorhynchus tshawytscha otolith pairs. We found mineralogical compositions frequently differed between otoliths in a pair and accurate calcium carbonate polymorph identification was rarely possible by visual inspection alone. The prevalence of multiple polymorphs in otoliths is not well-understood, and future research should focus on identifying otolith compositions and investigate how variations in mineralogy affect trace-element incorporation and potentially bias environmental interpretations.
... While calcite is a common CaCO 3 polymorph in invertebrates, it is rarely found in fish otoliths, and only some primitive species of fish have calcite, combined with vaterite, as the main CaCO 3 polymorph in their otoliths (Pracheil et al. 2017). Vaterite, but not calcite, otoliths are commonly found in many aquaculture-reared fish species (Gauldie et al. 1997;Whitley et al. 1999), and some authors have suggested that vaterite deposition is the result of abnormally high growth rates (Reimer et al. 2017) or high animal density in the farms (Austad et al. 2021). Functionally, transmission of sound waves through otoliths is significantly influenced by the size of the otolith and the presence of non-aragonite CaCO 3 polymorphs, indicating that ocean acidification might have a negative impact on fish hearing and navigation if size and/or CaCO 3 composition are affected (Bignami et al. 2013;Radford et al. 2021;Reimer et al. 2016). ...
... Although very rare, aragonite replacement by calcite can occur spontaneously in wild populations (Oliveira et al. 1996), but the reasons are still unknown. Some authors have suggested that aragonite can be replaced by other polymorphs such as vaterite when growth rates are increased (Reimer et al. 2017) or animal density is high (Austad et al. 2021). While possible changes in growth rate might be the reason for calcite deposition, the fact that only 10% of the animals were affected makes that assumption unlikely. ...
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To date the study of ocean acidification on fish otolith formation has been mainly focused on larval and juvenile stages. In the present pilot study, wild-captured adult Atlantic cod (Gadus morhua) were exposed to two different levels of pCO2, 422µatm (ambient, low pCO2) or 1091µatm (high pCO2), for a period of 30 weeks (from mid-October to early April 2014–2015) in order to study the effects on otolith size, shape and CaCO3 crystallization amongst other biological parameters. We found that otoliths from cod exposed to high pCO2 were slightly smaller (− 3.4% in length; − 3.3% in perimeter), rounder (− 2.9% circularity and + 4% roundness) but heavier (+ 5%) than the low pCO2 group. Interestingly, there were different effects in males and females; for instance, male cods exposed to high pCO2 exhibited significant changes in circularity (− 3%) and roundness (+ 4%) compared to the low pCO2 males, but without significant changes on otolith dimensions, while females exposed to high pCO2 had smaller otoliths as shown for length (− 5.6%), width (− 2%), perimeter (− 3.5%) and area (− 4.8%). Furthermore, while the majority of the otoliths analysed showed normal aragonite deposition, 10% of fish exposed to 1091µatm of pCO2 had an abnormal accretion of calcite, suggesting a shift on calcium carbonate polymorph crystallization in some individuals under high pCO2 conditions. Our preliminary results indicate that high levels of pCO2 in adult Atlantic cod might affect otolith growth in a gender-specific way. Our findings reveal that otoliths from adult cod are affected by ocean acidification, and we believe that the present study will prompt further research into this currently under-explored area.
... Several studies have reported abnormal otoliths which have different size, shape, and density as compared to normal otoliths in a number of freshwater and marine fishes (Sweeting et al. 2004;Oxman et al. 2007;Ma et al. 2008;Reimer et al. 2016). In the case of abnormal otoliths, the aragonite is replaced by vaterite but in some species, calcite may replace aragonite (Gauldie 1993;Campana 1999;Ma et al. 2008;Reimer et al. 2017). Various factors are responsible for aberrant otoliths such as stress, genetic and neuroendocrine factors but a limited number of studies have tested the effect of these factors (Tomas et al. 2004;Ma et al. 2008;Reimer et al. 2017). ...
... In the case of abnormal otoliths, the aragonite is replaced by vaterite but in some species, calcite may replace aragonite (Gauldie 1993;Campana 1999;Ma et al. 2008;Reimer et al. 2017). Various factors are responsible for aberrant otoliths such as stress, genetic and neuroendocrine factors but a limited number of studies have tested the effect of these factors (Tomas et al. 2004;Ma et al. 2008;Reimer et al. 2017). The replacement of aragonite by vaterite is usually higher in fish species that are hatchery-reared but this may also occur in wild fishes (Tomas and Geffen 2003). ...
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Otoliths are calcified structures and the information contained within their chemistry or shape can be used to infer life history events, migration patterns, and stock structure of a fish population. Understanding how otolith chemistry is affected by temperature, salinity, interactive effects of abiotic factors, ontogeny, physiology, etc. is essential for the reconstruction of the environment that affected the fish. Otolith shape is also affected by environmental conditions in addition to the genotype. The applications of otolith chemistry and shape for stock discrimination have increased in recent years because of the advancements in analytical methods and the related software. The stock identification methods sometimes provide variable results but if we use complementary approach the information generated could be more reliable which can be used to prepare effective management and conservation strategies. It appears warranted to generate more information on the factors influencing otolith chemistry and shape especially when two or more factors exert synergetic influence. Therefore, the objectives of this review paper were to provide comprehensive information on various factors influencing the otolith chemistry and shape, and the utility of otolith chemistry and shape for fish stock discrimination with an emphasis towards the research areas needing additional studies.
... Despite this, the release of hatcheryreared fish is a commonly used conservation technique, often applied to increase sturgeon stocks. Fish hatcheries often encourage enhanced growth by feeding enriched diets, increasing water temperatures, and using continuous light to encourage rapid growth rates 52 . The increased growth rate in hatchery reared fish likely impacts otolith matrix proteins resulting in the abnormal crystallization of otoliths in farmed fish and has been shown to result in hearing impairment in farmed salmonids 52 . ...
... Fish hatcheries often encourage enhanced growth by feeding enriched diets, increasing water temperatures, and using continuous light to encourage rapid growth rates 52 . The increased growth rate in hatchery reared fish likely impacts otolith matrix proteins resulting in the abnormal crystallization of otoliths in farmed fish and has been shown to result in hearing impairment in farmed salmonids 52 . For conservation hatcheries, where the primary goal is to produce offspring that are capable of survival post hatchery release and contribute to future populations 53 , it is important to ensure rearing practices do not have adverse effects on the development of individuals. ...
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Changes to calcium carbonate (CaCO 3) biomineralization in aquatic organisms is among the many predicted effects of climate change. Because otolith (hearing/orientation structures in fish) CaCO 3 precipitation and polymorph composition are controlled by genetic and environmental factors, climate change may be predicted to affect the phenotypic plasticity of otoliths. We examined precipitation of otolith polymorphs (aragonite, vaterite, calcite) during early life history in two species of sturgeon, Lake Sturgeon, (Acipenser fulvescens) and White Sturgeon (A. transmontanus), using quantitative X-ray microdiffraction. Both species showed similar fluctuations in otolith polymorphs with a significant shift in the proportions of vaterite and aragonite in sagittal otoliths coinciding with the transition to fully exogenous feeding. We also examined the effect of the environment on otolith morphology and polymorph composition during early life history in Lake Sturgeon larvae reared in varying temperature (16/22 °C) and pCO 2 (1000/2500 µatm) environments for 5 months. Fish raised in elevated temperature had significantly increased otolith size and precipitation of large single calcite crystals. Interestingly, pCO 2 had no statistically significant effect on size or polymorph composition of otoliths despite blood pH exhibiting a mild alkalosis, which is contrary to what has been observed in several studies on marine fishes. These results suggest climate change may influence otolith polymorph composition during early life history in Lake Sturgeon.
... Based on current knowledge, vaterite crystallization is associated with changes in the internal physiology of the fish and is possibly protein-mediated (as reviewed in Thomas & Swearer, 2019). For instance, Reimer et al. (2017) showed that fast-growing Atlantic salmon Salmo salar L. were three times more likely to have vaterite otoliths than slow-growing individuals were. The authors speculated that the difference could be caused, for example, by the greater energy content of fast-growing fish, which may lead to greater transport of bicarbonate ions (HCO 3 À ) relative to Ca 2+ into the endolymph and result in a lower (Ca 2+ )/(CO 3 2À ) ratio conducive for vaterite formation. ...
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We report observations of vateritic crystallization in the sagittal otoliths of the Baltic herring Clupea harengus membras in the northern Baltic Sea. While the existence of vaterite in the calcium carbonate matrix of sagittal otoliths has been observed in various species globally, reports from the brackish Baltic Sea are few in number. Large variation in the frequency of vaterite in 1984, 1988, 1997, 2010 and 2017 was observed, suggesting that the phenomenon is not static and more long-term studies should be conducted in search of the ultimate causing factors. This article is protected by copyright. All rights reserved.
... The calcium carbonate component is present in the form of polycrystalline aragonite for the majority of sagittae and lapilli (Carlström, 1963) but sporadic inclusion of the other common polymorphs vaterite and calcite can be found simultaneously to aragonite in some otoliths (Strong et al. 1986;Gauldie, 1993). Entirely vateritic sagittae and lapilli can also form aberrantly (Mugiya, 1972;Reimer et al. 2017) but vaterite seems to be the preferred form in most asteriscii (Lowenstam and Weiner, 1989;Oliveira et al. 1996). ...
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Near infrared spectroscopy (NIRS) is a light spectroscopy method useful for non-invasively discriminating and quantifying chemical composition of a wide variety of substances. Recently-developed applications of NIRS to fish age estimation across a range of taxa have sparked intense interest in exploring the feasibility of its use for rapid age estimation in fisheries population management. In this pursuit, development of species-specific calibration models relating traditionally-derived age estimates (i.e., those estimated from growth band counts) to NIR spectral signatures from ageing structures is required to derive predictive models that can then estimate age from rapid scans of whole ageing structures alone. Otoliths and corresponding traditionally-derived ages of juvenile and adult red snapper Lutjanus campechanus were used to generate NIRS models for predicting both daily and annual ages. NIRS-predicted daily ages were accurate to within six days of traditional estimates and were not significantly different than traditionally-derived ages for juveniles aged 39 – 120 days when used to produce length-at-age models. NIRS-predicted annual ages were accurate to within approximately one year in fish aged 0 – 30 years, but prediction error rose substantially for fish aged 31 – 38 years. Across all models, age-related otolith morphometric dynamics changed the physical interaction of NIR light with the structures and impacted the resolution of age prediction models. When size and otolith morphometrics for a subset of otoliths (n=26) were standardized by grinding and subsampling a fixed mass from each for NIRS analysis, NIRS prediction error increased by approximately 30% but ages remained accurate to within 2 years of traditional ages; hence, otolith structure is of some importance to predictive models but ontogenetic compositional changes underlie most of the correlation of NIRS otolith spectral signatures with age. Protein concentration (% otolith weight) was positively correlated with traditional age, but the impact of this relationship on otolith spectral signatures was not easily discernable. However, comparison of otolith spectral signatures to those of two primary otolith constituents, calcium carbonate and type I collagen, revealed that absorbance features at characteristic wavenumbers for each constituent were correlated to NIRS otolith age prediction, providing the first insights to the NIRS age-prediction mechanism in otoliths.
Stable isotope compositions of otoliths can be used to provide thermal histories of fish. This tool, however, is currently unrefined for catadromous species, such as the American eel Anguilla rostrata, where the otolith is formed in both marine and freshwater environments. We reared 2000 elvers in fresh water for 32 weeks in 10 temperature treatments ranging from 10 to 34 °C, and then measured δ¹⁸O and δ¹³C of otoliths to 1) determine how somatic and otolith growth responded to temperature; 2) evaluate the relationship between water temperature and δ¹⁸O and δ¹³C of otoliths; and 3) develop a species-specific isotopic fractionation equation that isolates the freshwater portion of the otolith. Our results show that eel elvers have a high optimum temperature for somatic growth (27–28 °C). Optimum temperature for otolith growth was slightly higher, suggesting that otolith growth can be decoupled from body growth. The expression for carbonate-water isotopic fractionation of American eel otoliths over the temperature range examined was 1000lnαaragonite-water = 14.30(10³ T⁻¹) – 18.651. This equation accurately predicted water temperature (predictive error 0.49 °C) for 180 American eel otoliths obtained from a different controlled rearing study (conducted at 22 and 28 °C). This experiment validated the use of the oxygen and carbon isotope compositions of otoliths to determine the thermal history of American eels in fresh water, thus providing a method that can be applied to wild eels.
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Atlantic salmon (Salmo salar) is one of the best researched fishes, and its aquaculture plays a global role in the blue revolution. However, since the 1970s, tens of millions of farmed salmon have escaped into the wild. We review current knowledge of genetic interactions and identify the unanswered questions. Native salmon populations are typically genetically distinct from each other and potentially locally adapted. Farmed salmon represent a limited number of wild source populations that have been exposed to ≥12 generations of domestication. Consequently, farmed and wild salmon differ in many traits including molecular-genetic polymorphisms, growth, morphology, life history, behaviour, physiology and gene transcription. Field experiments have demonstrated that the offspring of farmed salmon display lower lifetime fitness in the wild than wild salmon and that following introgression, there is a reduced production of genetically wild salmon and, potentially, of total salmon production. It is a formidable task to estimate introgression of farmed salmon in wild populations where they are not exotic. New methods have revealed introgression in half of ~150 Norwegian populations, with point estimates as high as 47%, and an unweighted average of 6.4% across 109 populations. Outside Norway, introgression remains unquantified, and in all regions, biological changes and the mechanisms driving population-specific impacts remain poorly documented. Nevertheless, existing knowledge shows that the long-term consequences of introgression is expected to lead to changes in life-history traits, reduced population productivity and decreased resilience to future challenges. Only a major reduction in the number of escapees and/or sterility of farmed salmon can eliminate further impacts.
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Background Domestication of Atlantic salmon for commercial aquaculture has resulted in farmed salmon displaying substantially higher growth rates than wild salmon under farming conditions. In contrast, growth differences between farmed and wild salmon are much smaller when compared in the wild. The mechanisms underlying this contrast between environments remain largely unknown. It is possible that farmed salmon have adapted to the high-energy pellets developed specifically for aquaculture, contributing to inflated growth differences when fed on this diet. We studied growth and survival of 15 families of farmed, wild and F1 hybrid salmon fed three contrasting diets under hatchery conditions; a commercial salmon pellet diet, a commercial carp pellet diet, and a mixed natural diet consisting of preserved invertebrates commonly found in Norwegian rivers. ResultsFor all groups, despite equal numbers of calories presented by all diets, overall growth reductions as high 68 and 83%, relative to the salmon diet was observed in the carp and natural diet treatments, respectively. Farmed salmon outgrew hybrid (intermediate) and wild salmon in all treatments. The relative growth difference between wild and farmed fish was highest in the carp diet (1: 2.1), intermediate in the salmon diet (1:1.9) and lowest in the natural diet (1:1.6). However, this trend was non-significant, and all groups displayed similar growth reaction norms and plasticity towards differing diets across the treatments. Conclusions No indication of genetic-based adaptation to the form or nutritional content of commercial salmon diets was detected in the farmed salmon. Therefore, we conclude that diet alone, at least in the absence of other environmental stressors, is not the primary cause for the large contrast in growth differences between farmed and wild salmon in the hatchery and wild. Additionally, we conclude that genetically-increased appetite is likely to be the primary reason why farmed salmon display higher growth rates than wild salmon when fed ad lib rations under hatchery conditions. Our results contribute towards an understanding of the potential genetic changes that have occurred in farmed salmon in response to domestication, and the potential mechanisms underpinning genetic and ecological interactions between farmed escapees and wild salmonids.
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The rapid growth of aquaculture raises questions about the welfare status of mass-produced species. Sagittal otoliths are primary hearing structures in the inner ear of all teleost (bony) fishes and are normally composed of aragonite, though abnormal vaterite replacement is sometimes seen in the wild. We provide the first widespread evaluation of the prevalence of vaterite in otoliths, showing that farmed fish have levels of vaterite replacement over 10 times higher than wild fish, regardless of species. We confirm this observation with extensive sampling of wild and farmed Atlantic salmon in Norway, the world's largest producer, and verify that vateritic otoliths are common in farmed salmon worldwide. Using a mechanistic model of otolith oscillation in response to sound, we demonstrate that average levels of vaterite replacement result in a 28-50% loss of otolith functionality across most of a salmonid's known hearing range and throughout its life cycle. The underlying cause(s) of vaterite formation remain unknown, but the prevalence of hearing impairment in farmed fish has important implications for animal welfare, the survival of escapees and their effects on wild populations, and the efficacy of restocking programs based on captive-bred fish.
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The percentage of hatchery-reared coho salmon Oncorhynchus kisutch in the Strait of Georgia, British Columbia, increased from nearly 0% in the early 1970s to more than 70% by 2001. These estimates were derived from fin clip and coded wire tag data collected from commercial and sport fisheries, research surveys conducted in the summer and fall of 1997 to 2000, and examination of the microstructure of otoliths extracted from juvenile coho salmon collected during our marine surveys. The increasing trend may be related to the proportions of hatchery and wild smolts entering saltwater, fishing rates, and changes in the ecological processes regulating coho salmon production in the ocean. The consequence for management is that the abundance of wild spawning salmon (escapement) depends on hatchery as well as wild production. The consequence for policy makers is that future enhancement activities need to have clear policies for assessing the effects of hatchery fish on the population dynamics of wild fish as well as for producing hatchery fish.
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Aragonite is the normal form of calcium carbonate found in teleost otoliths, but it is sometimes replaced by vaterite, an alternate crystalline structure. We investigated the assumption that sagittal otoliths with vaterite replacement were unique to stocked lake trout Salvelinus namaycush in the Laurentian Great Lakes. Earlier studies had attributed these abnormalities to stocking stress, and proposed that the presence of vaterite could separate individual unmarked stocked lake trout from their wild counterparts. We examined and described the frequency of vateritic sagittae in two wild and three stocked populations of lake trout from the Great Lakes and a wild population from a remote inland lake in northern Canada. Among lake trout caught 2–12 years after being stocked, prevalence of vateritic sagittae was 66% for Lake Superior fish, 75% for Lake Huron fish, and 86% for Lake Ontario fish. Among wild fish caught, vateritic sagittae were present in 37% of Lake Superior fish, 22% of Lake Huron fish, and 49% of northern Canada fish. We also compared year-to-year differences in prevalence in four year-classes of fingerling lake trout reared in two U.S. national lake trout hatcheries. Prior to release, between 53 and 84% of the hatchery fish had at least one vateritic sagitta, and prevalence increased with handling associated with hatchery practices. Vateritic sagittae in wild fish might also indicate stress in nature. The presence of vateritic sagittae in both wild and stocked fish compromises the use of this characteristic as an unequivocal indicator of a particular fish's origin. Among-population differences in both the prevalence and the extent of vaterite replacement, however, may provide a means of differentiating between stocks of sympatric unmarked wild and stocked lake trout.
First published in 1990, The Economics of Salmon Aquaculture was the first book to systematically analyse the salmon aquaculture industry, from both a market and production perspective. Since publication of the first edition of this book, the salmon aquaculture industry has grown at a phenomenal rate, with salmon now being consumed in more than 100 countries worldwide. This second edition of a very popular and successful book brings the reader right up to date with all the major current issues pertaining to salmon aquaculture. Commencing with an overview of the production process in aquaculture, the following chapters provide in-depth coverage of the sources of the world's supply of salmon, the growth in productivity, technological changes, environmental issues, markets, market structure and competitiveness, lessons that can be learnt from the culture of other species, optimal harvesting techniques, production planning, and investment in salmon farms. Written by Frank Ashe and Trond Bjørndal, two of the world's leading experts in the economics of aquaculture, this second edition of The Economics of Salmon Aquaculture provides the salmon aquaculture industry with an essential reference work, including a wealth of commercially important information. This book is also a valuable resource for upper level students and professionals in aquaculture and economics, and libraries in all universities and research establishments where these subjects are studied and taught should have copies of this important book on their shelves.
Although the physiological significance of the static organ is rather well established, little attention has been paid to the structure and composition of the dense bodies in the labyrinth of vertebrates. One exception is the work done on the well-known "ear-stones" of bony fishes. Ever since 1899, when Reibisch demonstrated that fish otoliths could be used for accurate age determinations, these bodies have been subjected to extensive studies. But on the whole, the information available regarding the nature of the calcareous deposits in the labyrinth of vertebrates other than teleosts is very meager. It has long been known that the dense bodies in the inner ear occur either as solitary large "ear-stones" or as masses of minute particles, "ear-dust." In what follows, the former will be referred to as "statoliths," and the latter as "statoconia." As is customary, the term "otolith" is used in a broader sense to mean any type of a dense body in the labyrinth. It is true that the function of statoliths and statoconia is not exclusively a static one (Lowenstein, 1950), but we prefer the use of these well-known terms to the introduction of entirely new ones. In the labyrinth of teleosts there are generally three large statoliths, each having an irregular unsymmetrical shape which is characteristic of the species. These bodies derive their names from their shape in carps: sagitta (arrow), lapillus (small stone), and asteriscus (star). They are located in sacculus, utriculus and lagena, respectively. Most other vertebrates, however, have otolith masses consisting of a very great number of small statoconia held more or less firmly together by an organic gel. The statoconia have microscopic dimensions, usually between 1 and 50 microns, are symmetrically shaped and are not characteristic for the species. Recently, otoliths having a size somewhere between statoliths and statoconia have been described by Frizzell and Exline (1958), who suggested the name "ossiculiths" (ossiculum bonelet + lithos stone) for such bodies. This term is rather unfortunate, not only because of the mixture of Latin and Greek, but especially because these bodies have nothing at all to do with bone. According to these authors, "ossiculiths" should be small (50-500 tL) plano-convex or irregularly shaped particles which are found occasionally with the ordinary statoliths of teleosts. However, in a high percentage of the individuals they occur in one of the labyrinths only, and are then often associated with malformed or abnormal statoliths (Weiler, 1959). "Ossiculiths" can thus hardly be regarded as normal formations in the teleost labyrinth. Irregularly shaped small bodies may, on the other hand, be found regularly together with statoconia, as in the labyrinth of the lamprey, Lamnpetra (Studnicka, 1912). In the labyrinth of sturgeons, Acipenser, all stages in shape and structure between statoconia and statoliths are found. Some of these intermediate-sized bodies have evidently