Do otolith increments allow correct inferences about age and growth of coral reef fishes?

Otolith increment structure is widely used to estimate age and growth of marine fishes. Here, I test the accuracy of the long-term otolith increment analysis of the lemon damselfish Pomacentrus moluccensis to describe age and growth characteristics. I compare the number of putative annual otolith increments (as a proxy for actual age) and widths of these increments (as proxies for somatic growth) with actual tagged fish-length data, based on a 6-year dataset, the longest time course for a coral reef fish. Estimated age from otoliths corresponded closely with actual age in all cases, confirming annual increment formation. However, otolith increment widths were poor proxies for actual growth in length [linear regression r ² = 0.44–0.90, n = 6 fish] and were clearly of limited value in estimating annual growth. Up to 60 % of the annual growth variation was missed using otolith increments, suggesting the long-term back calculations of otolith growth characteristics of reef fish populations should be interpreted with caution.     

Age and growth of the Black Sea turbot, Psetta maxima (Linneaus, 1758) (Pisces: Scophthalmidae), estimated by reading otoliths and by back-calculation

Age and growth of the Black Sea turbot, Psetta maxima, were determined from a total of 1445 individuals collected along the eastern Black Sea coast between 1990 and 1996. Age was estimated by interpreting growth rings in whole and broken sagittal otoliths. The former method underestimated the age over 5 years, and a maximum age of 11 years was observed by the latter. Marginal increment analysis clearly showed that a single annulus is formed in early summer each year. Growth in length differed between sexes, and females attained a larger size than males at the same age. No significant difference was found between the mean observed total length (TL), the back‐calculated TL derived from radius measurements and the TL estimated from otolith size–fish size relationship. The von Bertalanffy growth parameters estimated by the length‐at‐age data were: L_∞ = 96.24 cm; K = 0.119 year^?1; t₀ = ?0.01 year for the entire population.     

Validation of daily increment formation in otoliths for Gymnocypris selincuoensis in the Tibetan Plateau,China

Daily increment validation in fish otolith is fundamental to studies on fish otolith microstructure, age determination and life history traits, and thus is critical for species conservation and fishery management. However, it has never been done for Schizothoracine fish, which is the dominant component of fish fauna in the Tibetan Plateau. This study validated the daily increment formation of Gymnocypris selincuoensis, as a representative of Schizothoracine fish, by monitoring the growth of hatchery‐reared larvae group and wild‐caught post‐yolk‐sac larvae group under controlled experiments. The results from monitoring the hatchery‐reared larvae group showed that sagittae and lapilli were found in yolk‐sac larvae, and formed 5–7 days before hatching, but asterisci were not found until 11 days post‐hatching. The first increment in sagittae and lapilli was formed in the first day after hatching. The daily periodicity of increment formation was examined and confirmed in sagittae and lapilli of both larvae groups. However, sagittae were better for age determination than lapilli for larvae at earlier days. For larval G. selincuoensis older than 50 days, lapilli were the only otolith pair suitable for larvae daily age determination. This study validated the daily increment formation in Schizothoracine fish for the first time has primary implications to other fishes from this subfamily.     

Age and growth of the brick soldierfish,Myripristis amaena

Otoliths (sagittae) of the coral reef fish, Myripristis amaena, the brick solderfish were examined internally by Scanning Electron Microscope methods to observe microincrements. The daily nature of increment deposition was validated through tetracycline and acetazolamide marking experiments. Utilization of multivariant mathematical models relating age to otolith size and fish size demonstrated that age could be reliably determined from body measurements and otolith weight measurements. Consequently, M. amaena grows slowly, maturing at about 6 years of age, lives at least 14 years and reaches at least 215 mm SL.     

Otolith increment width responses of juvenile Australian smelt Retropinna semoni to sudden changes in food levels: the importance of feeding history

To aid the interpretation of otolith microstructure in wild fishes, the present study assessed responses in daily otolith increment widths of early juvenile Australian smelt Retropinna semoni to sudden changes in feeding conditions. There was an almost immediate response in otolith increment widths (which can be interpreted as growth in length) to sudden changes in feeding conditions, with such changes being detected statistically after c. 4 days. Fish displayed compensatory growth when food supplies were increased following a period of limited food, indicating the magnitude of the response in growth appears highly dependant on feeding history. Additionally, fish size also appeared to influence increment widths suggesting that both fish size and feeding history are important factors that must be considered when interpreting otolith microstructure for the species.     

Rhythmic structural and chemical patterns in otoliths of the Antarctic fish Notothenia larseni: Their application to age determination

Summary Sagittal otoliths from Notothenia larseni contain microincremental growth rings which are distinctly visible in otolith sections using Scanning Electron Microscopy. These microincrements are similar to those deposited daily in the otoliths of fishes from temperate and tropical waters. Microincrements were easily enumerated and fish length was related to increment number by a logarithmic curve. Otolith microstructure analysis appears to provide a technique to accurately determine age and growth rates in these fish. Sr/Ca ratios in otolith aragonite were analyzed along a radius from the outside edge to the core of an otolith section using an electron microprobe. The strontium/calcium (Sr/Ca) ratios varied with a cyclic periodicity apparently related to seasonal water temperature cycles and the number of cycles agreed closely with age estimated from daily microincrement counts. Sr/ca cycles can potentially be used to determine age, validate growth rates determined by other methods, and establish thermal conditions experienced during the life of a fish. Microstructural and chemical analyses of otoliths demonstrate great potential in helping to answer many questions about the growth processes and ecology of Antarctic fishes.     

Validation of daily otolith increments in larval and juvenile Chinese sucker, <Emphasis Type="Italic">Myxocyprinus asiaticus</Emphasis>

Otolith development was observed and the formation of daily growth increments in otoliths of Chinese sucker, Myxocyprinus asiaticus, was validated by monitoring known-age larvae and juveniles in the laboratory from 2003 to 2005. Otolith shape changed with larval and juvenile development, and there was an exponential relationship until a body length of 16 mm or so, and a linear relationship after a body length of 16 mm between otolith size and fish size. The first increment was identified in larvae 1 day after hatching. The regressed equations between daily age (D) and increment number in otoliths (N) were N = −0.64 + 0.96D in lapillus, and N = −0.31 + 0.98D in sagitta. The slopes were not significantly different than 1.0. This demonstrated that otolith increments in this species were formed daily and can be used for daily age determination.     

The use of otolith microstructure to estimate age in adult Atlantic cod Gadus morhua

Transverse sections of otoliths from Atlantic cod Gadus morhua from the Baltic Sea revealed narrow growth increments. The widths of these increments corresponded to daily increments from fish with known otolith growth rates and were therefore assumed to be daily increments. They exhibited a distinct pattern with increasing distance from the primary primordium. A series of zones with clearly distinguishable increments, first with increasing then with decreasing widths in a dome‐shaped pattern, were separated by zones where no regular increment structure was visible. Increment width seemed to be tightly coupled to the annual cycle in environmental temperature at a depth of 30–60 m, where G. morhua predominantly reside. Between 135 and 200 increments occurred within the different zones, with a non‐significant trend towards lower increment numbers and widths with distance from the primary primordium of the otolith. Increment formation apparently ceased at temperatures < 5–6° C, but growth during the cold months corresponded closely with estimated growth rates. The increment patterns seemed to reflect annual cycles in environmental temperature, and the count of the increment cycles may thus be a promising tool for the determination of the true age of Baltic G. morhua.     

Seasonal and inter-stream variations in the population dynamics, growth and secondary production of an algivorous fish (Pseudogastromyzon myersi: Balitoridae) in monsoonal Hong Kong

1. Balitorid loaches are widespread and highly diverse in Asian streams, yet their life history and ecology have received little attention. We investigated seasonal (wet versus dry season) and spatial variation in populations of algivorous Pseudogastromyzon myersi in Hong Kong, and estimated the magnitude of secondary production by this fish in pools in four streams (two shaded and two unshaded) over a 15‐month period. 2. Mean population densities of P. myersi ranged from 6.0 to 23.2 individuals m⁻², constituting more than half (and typically >70%) of benthic fishes censused. Abundance was c. 25% greater in the wet season, when recruitment occurred. Significant density differences among streams were not related to shading conditions and were evident despite small‐scale variations in P. myersi abundance among pools. Mean biomass varied among streams from 0.85 to 3.87 g ash‐free dry weight (AFDW) m⁻². Spatial and seasonal patterns in biomass and density were similar, apart from some minor disparities attributable to differences in mean body size among populations. 3. All four P. myersi populations bred once a year in June and July, and life spans varied from 24 to 26 months. Populations consisted of three cohorts immediately after recruitment but, for most of the study period, only two cohorts were evident. Cohort‐specific growth rates did not differ significantly among streams but, in all streams, younger cohorts had higher cohort‐specific growth rates. 4. Secondary production of P. myersi estimated by the size‐frequency (SF) method was 2.7–11.5 g AFDW m⁻² year⁻¹ and almost twice that calculated by the increment‐summation (IS) method (1.2–6.6 g AFDW m⁻² year⁻¹). Annual P/B ratios were 1.17 – 2.16 year⁻¹ (IS) and 2.73 – 3.22 year⁻¹ (SF). Highest production was recorded in an unshaded stream and the lowest in a shaded stream, but site rankings by production did not otherwise match shading conditions. Wet‐season production was six times greater than dry‐season production, and daily production fell to almost zero during January and February. Cool temperatures (<17 °C) may have limited fish activity and influenced detectability during some dry‐season censuses. Estimates of abundance and annual production by P. myersi are therefore conservative. 5. Comparisons with the literature indicate that the abundance and production of P. myersi in Hong Kong was high relative to other benthic fishes in tropical Asia, or their temperate counterparts in small streams. Manipulative experiments are needed to determine the influence of P. myersi, and algivorous balitorids in general, on periphyton dynamics and energy flow in Asian streams.     

Comparison of otolith growth and morphology with somatic growth and age in young-of-the-year bluefin tuna

Otolith morphological characteristics were studied using image analysis techniques and the relationships between otolith growth and somatic growth and age, as estimated from counting daily otolith increments, were examined in young-of-the-year (YOY) bluefin tuna Thunnus thynnus ranging in fork length ( L _F) from 8·5 to 55·5 cm. Whole otolith length, width, area and perimeter, and three shape indexes, circularity, E value and rectangularity, were extracted for each pair of sagittae. Since no statistical significant differences between left and right otolith morphometrics were found, only one otolith from each fish was used for correlations. Statistically significant relationships were observed between otoliths measurements and fish somatic growth when a linear regression was applied after logarithmic transformation of all variables tested. Among the variables, otolith length was the one that showed the highest correlation with L _F, followed by otolith area and perimeter, whereas otolith rectangularity exhibited the lowest correlation. Statistically significant relationships were also observed between the otolith variables tested and the age of the fish, which ranged from 20 to 129 days. The ages estimated using otolith mass were very close to those assessed using daily increment counts (bias ranged from 1 to 24 days). Therefore, otolith mass could represent a valuable criterion for age estimation in YOY bluefin tuna that is objective, economic and easy to perform compared to daily increment counting method.     

Age structure, growth and survival rates of the commercial fish Prochilodus nigricans (bocachico) in North-eastern Ecuador

The bocachico, Prochilodus nigricans, is a commercially important fish distributed throughout the central and western Amazon. Age and growth of this species in eastern Ecuador were determined by otolith and scale increment analyses. For otolith analyses, we used thin sections of the astericus, and clear visualization of annuli required the use transmitted polarized light. Accuracy and precision of age estimation were compared to select the best ageing structure. Precision indices showed that otoliths are more reliable than scales to determine the age of bocachicos. Based on marginal increments analysis, we found that annulus formation in both structures occurs once a year between August and December. Seasonal changes in growth were associated with hydrological cycle of the river. The Ecuadorian Prochilodus at the juvenile–adult stage grew faster (i.e., K = 0.29 for ages 2 and older) than conspecific populations from Bolivia and Brazil (K = 0.5). In addition, annual mortality rate (A = 0. 56) was lower than reported for Prochilodus populations elsewhere in the Amazon. We conclude that this population is presently not overexploited, but conservation and management schemes for this population will need to consider that it is an international, trans-boundary migrant.     

Age and growth validation of the small spotted grunt Pomadasys commersonnii (Lacepède, 1801) from the northwestern coast of the Arabian Sea of Oman

Age structure and growth parameters were determined for a population of small spotted grunt, Pomadasys commersonnii in the Arabian Sea. Small spotted grunt samples were collected monthly between September 2007 and August 2008 by beam trawl [40 mm cod‐end mesh size] surveys conducted along the Arabian Sea coast of Oman from Ras Al‐Had in the north to the Oman‐Yemen border in the south west of Salalah between latitudes 16^o 33′N and 22^o 21′N and longitude 53^o 09′ and 59^o 55′ E and from depths of 20 to 250 m respectively. Marginal increment analysis of the sagittal otolith confirmed the deposition of annual increments on transverse sections, validating this technique for age and growth studies. Fish size (Fork Length, FL) ranged between 33–78 cm and age of fish ranged between 2 and 14 years with 5–9 years old fish comprising the majority of the catch. Both males and female exhibited asymptotic patterns of growth and the combined growth curve for both sexes provided von Bertalanffy growth (VBG) parameters of L_∞ = 77.2 cm FL (≡83.8 cm Total Length), k = 0.232/y and t₀ = ?0.058 y. VBG parameters, derived from Length‐Frequency Distribution Analysis (LFA) using ELEFAN1, PROJMAT and SLCA, obtained similar values (average values for the 3 methods: L_∞ = 78.8 cm FL, k = 0.35/y and t₀ = ?0.64 y) to those obtained from otolith analysis. A strong linear relationship was observed between otolith weight and age, and although age residuals ±4 years was observed between sagittal otolith age and estimated age (depending on sex and otolith weight), the results indicated that otolith weight could be used as a rapid proxy to estimate age and derive VBG parameters. In conclusion, both otolith ageing and LFA methods provided similar L_∞ and k values and the average values derived from all 4 methods lies within the auximetric plot for the species providing confidence in the VBG parameters obtained for small spotted grunt in the Arabian Sea.     

Forensic biological pursuits of exotic fish origins: piranha in Hawaii

Synopsis The otoliths of an adult red-bellied piranha, Pygocentrus nattereri, captured from a reservoir in Hawaii were scrutinized to determine the fish's origin and growth history. Sagittal otoliths of the piranha, P. nattereri, contained internal microincrements visible by Scanning Electron Microscopy. The medial cross sectional plane of the sagitta was resolved to provide counts for the most visible micro-increments. An opportune spawning of confiscated adults provided samples for verification of daily increment formation. Daily formation of microincrements was verified from hatched individuals, and confirmed the suitability of otoliths for revealing daily patterns in the age and growth of piranhas. The central area of the sagitta was diffuse in regards to otolith microstructure and indicated the fish was held in an unchanging environment (aquarium). Therefore, otoliths provide important life history or forensic information incorporated within their structural components. The visualization of daily microincrements in the otolith of a juvenile allowed the determination of age at and since release. Fish grew rapidly after being released into the wild. From otolith increments the date of release for an individual fish can be calculated with acceptable accuracy. As presented, otolith structural information can provide age and growth data which are essential to the management of introduced species.     

Age estimates derived from hard parts of swordfish Xiphias gladius from the north-western Mediterranean Sea

Accurate age estimates for fish are critical for properly understanding stock dynamics and health; this is particularly true for larger billfishes. Here we determined the most accurate aging estimation methods for swordfish (Xiphias gladius). We compared age estimates obtained from fin-ray sections, otolith sections, whole otoliths, and vertebrae collected from 87 swordfish off the east coast of Corsica. Age estimates from otolith sections were most consistently estimated across different readers (lowest average percentage error), followed by fin-ray sections, third vertebrae, and whole otoliths. When the age estimates from the otolith sections were compared with the other three age sclerochronological methods, we found the average percentage error to be lowest between the otolith section and fin-ray methods. However, age estimates from fin rays proved most useful for estimating swordfish younger than 6 years, as the fin ray-based age diverged from that of the otolith sections as the swordfish aged. Combining fin ray and otolith section techniques, we estimated the growth parameters of 1–12-year-old females (L_∞ = 259.412, k = 0.113, t₀ = −2.499) and 1–7-year-old males (L_∞ = 175.543, k = 0.202, t₀ = −2.239). We found that females grew significantly faster than males after 3 years and remained larger thereafter. Our calculated growth rates for this region of the north-western Mediterranean Sea were lower than those of the Atlantic, Pacific, and eastern Mediterranean Sea swordfish populations, and similar to growth rates recorded for the western Mediterranean Sea populations. Our study provides critical knowledge on biological-related parameters to serve as a guide for preserving the swordfish population in the Mediterranean Sea.     

The relationship between otolith size and estimated age of tigertooth croaker (Otolithes ruber Bloch and Schneider, 1801) in Oman Sea,Iran

The relationships between somatic growth and otolith dimensions, otolith size to estimated age and growth parameters of the tigertooth croaker (Otolithes ruber) were investigated in 100 specimens (size range: 19.1–52.0 cm, total length) from the Oman Sea area, September 2014. All 100 otoliths were sectioned and determined by age. The oldest specimen was a 4.5‐year‐old female with a total length of 40.6 cm; the youngest specimen was also a female estimated at 1 year of age with a total length of 19.1 cm. The von Bertalanffy growth equation was estimated as L_t = 54.70 (1 ? exp (?0.37 (t + 0.21))). Concluded was that there is a significant relationship between body size, otolith dimensions and estimated age of Otolithes ruber.     

Age estimation and lead�Cradium dating of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea

Antarctic toothfish (Dissostichus mawsoni) are the target of an important commercial fishery in the Southern Ocean, yet age data used for management have not been comprehensively tested for accuracy. In this study, Antarctic toothfish were aged using counts of otolith growth zones based on criteria established for Patagonian toothfish, D. eleginoides, a closely related species. To validate these ages, the radioactive disequilibrium of lead-210 and radium-226 in otolith cores was measured and used as an independent chronometer to accurately determine age across the range of fish caught in large numbers by the fishery. Growth-zone counts indicated Antarctic toothfish live to at least 39 years of age, and were in close agreement with the chronometer, validating the age estimation criteria and the accuracy of age estimates. Von Bertalanffy growth function parameters indicated Antarctic toothfish were relatively slow-growing (k = 0.111), especially in relation to their maximum size (L _∞ = 158.9 cm).     

The relationship between somatic growth and otolith dimensions of Mediterranean horse mackerel (Trachurus mediterraneus) from the Black Sea

In this study the relationships between somatic growth and otolith dimensions of Mediterranean horse mackerel (Trachurus mediterraneus) were investigated from samples obtained in the southeastern Black Sea area. It was concluded that there is a significant relationship between fish size and otolith dimensions. Therefore, age of Mediterranean horse mackerel can be estimated from otolith length and weight with sufficient certainty. This research was the first study of these relationships for T. mediterraneus from the Black Sea.     

The Morphology and Periodic Structures of the Otolith of the Chinook Salmon (Oncorhynchus tshawytscha), and Temperature-dependent Variation in Otolith Microscopic Growth Increment Width

The otolith (sagitta) of the chinook salmon (Oncorhynchus tshawytscha) has a variable external crystalline morphology which is related to differences in the growth rate of crystals in different parts of the otolith. The internal crystal structure of the otolith is complex with different mineral phases in different growth fields of the otolith and a well-defined series of microscopic growth increments in both the dorsal and the ventral parts (orientation in situ) of the otolith. The period of the microscopic growth increments was shown, by both a rearing experiment and interpolation from fish of known age, to be daily. By rearing sibling chinook salmon at different temperatures (while still maintaining them on the same diet) it was shown that the width of the daily growth increment varies with temperature, but neither multi- nor sub-daily increments appear in the area of regular, daily growth incrementation. Inclusions of the vaterite morph of calcium carbonate crystallizing in the botryoidal habit occur in the otherwise aragonitic otolith. Regularly spaced check rings in the sulcul part of the otolith are homologous with those occurring in the dorsal and ventral growth axis and are. on average, separated by about 28 microincrements.     

The growth of the common two-banded seabream, Diplodus vulgaris (Teleostei, Sparidae), in Canarian waters, estimated by reading otoliths and by back-calculation

The yearly nature of increment formation in the otoliths of 1–9‐year‐old seabream, Diplodus vulgaris (E. Geoffrey Saint‐Hilaire 1817), from the Canary Islands was validated. The marginal increment method showed that the opaque rings were formed in summer, and the translucent rings in winter. The Brody Proportional Hypothesis and the power length–radius relationship used to back‐calculate the growth trajectories of D. vulgaris showed that this growth model could provide reasonable growth estimates in this species. Growth back‐calculation and growth estimates obtained by direct otolith readings were similar. Data on age and size used to estimate the parameters of the von Bertalanffy growth model for D. vulagris from the Canary Islands showed that males and females had similar growth rates.     

The timing of early life events and growth rate estimates of age‐0 year group brill Scophthalmus rhombus along the west coast of Ireland

The timing of spawning and hatching, larval durations and growth exhibited by juvenile brill Scophthalmus rhombus captured along the Irish west coast were estimated using otolith microstructure analysis. Scophthalmus rhombus were estimated to have hatched between February and May, with fish settling onto nursery grounds between March and June. Fish collected later on in the season exhibited higher otolith growth rates in comparison to earlier collected fish. This is the first study to describe the early life history of a commercially valuable but understudied flatfish species.