Daily Growth Increments In Otoliths Research Articles

Juvenile downstream migration patterns of an anadromous fish, allis shad (Alosa alosa), before and after the population collapse in the Gironde system, France.

Diadromous fish have exhibited a dramatic decline since the end of the 20th century. The allis shad (Alosa alosa) population in the Gironde-Garonne-Dordogne (GGD) system, once considered as a reference in Europe, remains low despite a fishing ban in 2008. One hypothesis to explain this decline is that the downstream migration and growth dynamics of young stages have changed due to environmental modifications in the rivers and estuary. We retrospectively analysed juvenile growth and migration patterns using otoliths from adults caught in the GGD system 30 years apart during their spawning migration, in 1987 and 2016. We coupled otolith daily growth increments and laser ablation inductively-coupled plasma mass spectrometry measurements of Sr:Ca, Ba:Ca, and Mn:Ca ratios along the longest growth axis from hatching to an age of 100 days (i.e., during the juvenile stage). A back-calculation allowed us to estimate the size of juveniles at the entrance into the brackish estuary. Based on the geochemistry data, we distinguished four different zones that juveniles encountered during their downstream migration: freshwater, fluvial estuary, brackish estuary, and lower estuary. We identified three migration patterns during the first 100 days of their life: (a) Individuals that reached the lower estuary zone, (b) individuals that reached the brackish estuary zone, and (c) individuals that reached the fluvial estuary zone. On average, juveniles from the 1987 subsample stayed slightly longer in freshwaterthan juveniles from the 2016 subsample. In addition, juveniles from the 2016 subsample entered the brackish estuary at a smaller size. This result suggests that juveniles from the 2016 subsample might have encountered more difficult conditions during their downstream migration, which we attribute to a longer exposure to the turbid maximum zone. This assumption is supported by the microchemical analyses of the otoliths, which suggests based on wider Mn:Ca peaks that juveniles in 2010s experienced a longer period of physiological stress during their downstream migration than juveniles in 1980s. Finally, juveniles from the 2016 subsample took longer than 100 days to exit the lower estuary than we would have expected from previous studies. Adding a new marker (i.e., Ba:Ca) helped us refine the interpretation of the downstream migration for each individual.

Oceanic water temperatures less than 20°C may largely adjust for underestimation of European elver otolith ages

AbstractEuropean eel Anguilla anguilla otolith‐based elver ages may be substantially adjusted higher by migratory path oceanic water temperatures. Water temperatures <20°C increased temperature‐adjusted otolith ages of Japanese glass eels and elvers. Migration periods to the northern Vilaine and Severn Rivers were estimated at 785 days (2.15 years) and 781 days (2.14 years), respectively, and 958 days (2.62 years) for the southern Rio Minho, assuming a mean spawning date of 9 February (66 days shorter with a mean spawning date of 16 April). For a 9 February mean spawning date, temperature‐corrected otolith ages were higher than otolith ages by 34.4–92.7%. Higher migration route water temperatures reduced the temperature‐adjustment of otolith ages. Another approach to the temperature‐correction of otolith ages underestimated by 5.6–28.1% the migration period (days) to the southern Rio Minho and overestimated by 12.4–13.4% that to the two northern rivers. The effect of recent higher North Atlantic water temperatures on otolith daily growth increments remains to be learned. The difference between temperature‐adjusted otolith and observed ages differed little between earlier and later mean spawning dates. Otolith ages for glass and elver European eels should not be used if unadjusted for migration route water temperatures and used cautiously after adjustment for low oceanic, estuarine, and perhaps freshwater temperatures; even then otolith ageing issues remain. A greater understanding of oceanic migratory paths and durations is needed for European eels.

Oceanic Water Temperatures Less Than 20°C May Partly Account for Bias in American Eel Elver Otolith Age Estimates

AbstractThe mystery of the discrepancy between American Eel Anguilla rostrata larval, glass, and elver ages derived from otolith examination and from observed spawning and recruitment dates is long standing. A variety of solutions have been proposed but none have been validated. Japanese Eels Anguilla japonica do not deposit daily otolith growth rings at water temperatures ≤10°C and have less than daily deposition at temperatures 10–20°C, which may apply to American Eels. Oceanic water temperatures ≤10°C between continental sites and the Gulf Stream during glass and elver eel migration periods have little effect on ages imputed from otolith ring counts of eels migrating to sites south of Cape Hatteras because coastal water temperatures infrequently, and usually only for a few days, decline below 10°C between Cape Hatteras and South Carolina. Coastal and estuarine water temperatures of 10–20°C may have more effect. North of Cape Hatteras, the temperature effect on otolith ages increased with distances north of and from the Gulf Stream. Adjustment to otolith ages for low estuarine/freshwater temperatures may more fully account for the difference between otolith and observed ages over the recruitment period at sites north and south of Cape Hatteras. The effect of recent higher oceanic water temperatures north of Cape Hatteras on otolith daily growth increments remains to be learned but may increase otolith age estimates. Otolith ages for glass and elver American Eels should be used with caution unless adjusted for seasonal low oceanic, estuarine, and freshwater temperatures; even then otolith aging issues remain. A greater understanding of oceanic migratory paths and durations is needed for American Eels.

Hatching Time and Early Growth of Diplodus sargus sargus Inhabiting a Coastal Area of Gökçeada Island, Turkey

Daily growth increments in sagittal otoliths were used to estimate the age and growth of young of the year (YOY) white seabream, Diplodus sargus sargus collected between June 2013 and June 2014 at 6 different locations in the shallow waters (<20 m) off Gokceada, Turkey. Estimated ages from otolith daily growth increments (DGI) were found 42–238 days old. The mean daily growth rate of YOY D. sargus sargus was estimated as 0.046 cm/day. ANCOVA indicated that there was significant difference in daily growth rates between the locations (F = 22.92, df = 5, P < 0.001). The maximum daily growth rate of 0.055 cm/day was found in the location 2, while the minimum value of 0.037 cm/day was observed in the location 4. Hatching time was determined by subtracting the daily age of the fish from the sampling date and then hatch date frequency distributions were determined to occur from January through June, and 2 main hatching peaks were observed from the different locations. Linear relationships between otolith morphology (otolith length; OL, width; OW and radius; OR) and fish length (TL) were obtained.

Characteristics of two populations of Thai river sprat Clupeichthys aesarnensis from man-made reservoirs in Thailand and Laos, with aspects of gonad development

Growth and reproduction of the Thai river sprat Clupeichthys aesarnensis (Teleostei: Clupeidae) in Sirindhorn Reservoir, Thailand, and Nam Ngum Reservoir, Laos, were investigated using age estimates obtained from daily growth increments in otoliths and gonad observations. This species breeds throughout the year in both reservoirs, although water temperature was higher in Sirindhorn than in Nam Ngum. The Sirindhorn population tended to mature at smaller size (length) and younger age than the Nam Ngum population; the Sirindhorn population also tended to grow faster before reaching sexual maturity, growing slowly afterwards, than did the Nam Ngum population. Additionally, the maximum size in the Sirindhorn population was observed to be smaller than that of the Nam Ngum population. These observations indicated that higher water temperature resulted in earlier maturation and smaller maximum size in C. aesarnensis. Meanwhile, the smaller maximum size observed in the Sirindhorn population was possibly caused by an evolutionary down-sizing resulting from the overexploitation of this population, because Sirindhorn reservoir is exposed to more intensive fishing pressure.

Relationships between the daily growth rate of Japanese anchovy Engraulis japonicus larvae and environmental factors in Osaka Bay, Seto Inland Sea, Japan

Seasonal changes in the growth rate of larval Japanese anchovy Engraulis japonicus collected by shirasu seine net boats in Osaka Bay in 2008 were estimated using otolith daily growth increments to examine the effects of environmental factors. Larval anchovy were caught from May to November. The range in standard length (SL) of the larval anchovy was 10–35 mm, and larvae of SL 20–25 mm dominated numerically, accounting for more than 40% of all anchovy larvae. Daily growth rates for the last five days before catch increased from May to July, decreased or were stagnant in August and September, increased again in October, and decreased in November. Seawater temperature and density of copepod nauplii were correlated with the daily growth rate. In this study, the relationship between growth rate and temperature showed a skewed dome shape, with an optimum temperature for growth of around 23 °C. These results in summer of 2008 suggest that the growth rate of Japanese anchovy increased with increasing temperature for temperatures < 23 °C, but growth was limited by prey availability and/or other factors, such as low dissolved oxygen, at higher temperatures. Recent environmental improvements in nutrient inputs to Osaka Bay are discussed in relation to larval growth rate.

Juveniles recruitment and daily growth of the southern stock of Mugil liza (Actinopterygii; Fam. Mugilidae): new evidence for the current life-history model

Mugil liza is distributed along the western Atlantic coast. It is a commercially exploited species in Argentina, supporting a small-scale fishery conducted by an artisanal fleet. Age determination of fishes constitutes an important key issue for fishery management. The age, growth and recruitment of M. liza juveniles in Mar Chiquita coastal lagoon and Las Brusquitas creek (Buenos Aires, Argentina), were estimated by means of the analysis of the sagittal otoliths of fish collected during January to December of 2014. Ages were estimated by counting and measuring daily growth increments in otoliths under a light microscope. A total of 735 specimens ranging from 19 to 71.5 mm SL and from 67 to 212 days age was analysed. Lengths at previous ages were determined by back-calculation, a linear growth model was fitted to the back-calculated data: SL = 0.2468 + 2.0516; R2 = 0.9945. Two peaks of recruiters were observed from February to March, and from October to November in 2014. Mean ages in days of Querimana and juveniles at the recruitment time were 84.07 ± 14.43 days and 87.56 ± 19.51 days, respectively. The hatching dates of specimens showed two spawning seasons. One was from December 2013 to January 2014, and the second one from July to August 2014. The assessment carried on this work generated age determination values that support previous findings, contributing to make a more accurate description of the life-history model currently used. In addition, valuable information has been generated to give better advice for improving the management of the fishery resource.

Growth‐Increment Formation Using Otoliths and Scales for Age‐0 Chinook Salmon

AbstractRetrospective analysis is used to reconstruct fish body size at previous ages, with size and growth assumed to be accurately reflected by scale circuli and otolith increments. Using a 122‐d laboratory experiment, this study validated the relationship between fish body size and growth with scale circuli and otolith daily growth increments for age‐0 Chinook Salmon Oncorhynchus tshawytscha. Somatic growth was accurately reflected by growth in scale radius and growth in otolith diameter, indicating that growth in these two measures was proportional to growth in fish length. Although the width between scale circuli reflected somatic growth, daily growth was not accurately reflected by the width between corresponding otolith daily increments. Study results showed that fish deposited new otolith increments on a daily basis, but that new scale circuli were deposited at each successive increase of 5 to 6 mm in total length. These findings provide a foundation for future retrospective growth analyses involving Chinook Salmon and allow for the conversion of otolith and scale measurements into fish lengths, which are meaningful in studies of growth and survival.Received November 5, 2015; accepted April 8, 2016 Published online August 26, 2016

Does Daily Growth Affect the Rate of Manganese Uptake in Juvenile River Herring Otoliths?

AbstractManganese is a commonly found constituent in fish otoliths, yet a direct correlation with ambient water concentrations as observed for other elements has proven elusive. There is compelling evidence that Mn uptake is related to the availability of reduced Mn (Mn2+) resulting from hypoxia (Limburg et al. 2015) but that fish growth rate also plays a role. We tested the latter possibility by examining otoliths from anadromous river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) in New York waters. A significant correlation was found between the ages at which shifts in otolith daily growth increments (assumed proportional to somatic growth) and shifts in otolith Mn:Ca ratios were detected. Furthermore, significant positive Spearman's rank correlations were observed between mean otolith daily growth and otolith Mn:Ca. Species‐ and site‐specific differences were evident, but significant positive correlations were found for these relationships within each species and at most sampling sites. Ambient water concentrations were weakly correlated with otolith Mn:Ca, suggesting that both exogenous and endogenous factors influence Mn:Ca in otoliths. Thus, while endogenous mechanisms (i.e., growth rate) likely influence Mn uptake, exogenous availability is the ultimate control.

Age estimation of juvenile European hake Merluccius merluccius based on otolith microstructure analysis: a slow or fast growth pattern?

The main goal of this study was to examine otolith microstructure and to estimate the age and growth of European hake Merluccius merluccius from the eastern Mediterranean Sea. One hundred and twenty-nine specimens ranging from 102 to 438 mm in total length (LT ) were used. Age estimations were based on the study of the otolith microstructure, which was revealed after grinding both frontal sides of otoliths. The enumerations of the daily growth increments (DGI) as well as their width (WDGI ) measurements were made on calibrated digital images. The number of DGI in otoliths ranged between 163 and 717. Four phases in the WDGI evolution were distinguished: (1) larval-juvenile pelagic phase, with an increasing trend in WDGI up to the 60th DGI, (2) settlement phase, with a short-term deceleration in WDGI between the 61st and 150th DGI, (3) juvenile demersal phase, characterized by a stabilization of WDGI from 151st to 400th DGI and (4) adult phase, with a decreasing trend in WDGI after the 400th DGI. Age, sex and month of formation were found to affect the WDGI in all phases, with the exception of age at the juvenile demersal phase. The power curve with intercept model described best the relationship of M. merluccius LT with age (TDGI ), according to Akaike criteria, revealing differences in growth between females [LT = 65 · 36(TDGI )(0 · 40) - 388 · 55] and males [LT = 69 · 32(TDGI )(0 · 37) - 352 · 88] for the sizes examined. The mean daily growth rates were 0·61 mm day(-1) for females and 0·52 mm day(-1) for males, resulting in an LT of 283 and 265 mm at the end of their first year of life. In comparison with previous studies on the Mediterranean Sea, the results of this study showed a greater growth rate, similar to results from tagging experiments and otolith microstructure analyses for M. merluccius in other geographic areas.

문치가자미(Pseudopleuronectes yokohamae) 치어의 이석 일륜을 이용한 성장 및 산란시기 추정

2011년 2월부터 5월까지 경남 남해군 연안에서 소형 Beam trawl에 채집된 문치가자미 치어 이석을 관찰 분석하여 부화시기와 초기성장을 추정하였다. 문치가자미 치어는 2011년 2월에서 5월까지 총 175개체가 채집되었며, 체장-체중 관계식은 <TEX>$W=9.76^*10^{-8}L^{4.39}$</TEX> (<TEX>$r^2=0.93$</TEX>)를, 체장-이석경 관계식은 L=0.0795R+0.2249 (<TEX>$r^2=0.92$</TEX>)로 추정되었다. 체장 성장은 <TEX>$L_t=135{\exp}\{-{\exp}[0.0103(t-116)</TEX><TEX>]</TEX><TEX>\}$</TEX> (<TEX>$r^2=0.83$</TEX>)로 Gompertz 성장식이 가장 유의하게 회귀되었다. 이석 일령으로부터 추정한 주 산란시기는 12월에서 1월인 것으로 추정되었다. Hatching date, main spawning period and growth of juvenile marbled flounder (Pseudopleuronectes yokohamae) were determined by analysis of microstructure in otoliths. Marbled flounders were collected by a small beam trawl in Namhae from February 2011 to January 2012. The length (L, mm) was related to body weight (W, g); <TEX>$W=9.76^*10^{-8}L^{4.39}$</TEX> (<TEX>$r^2=0.93$</TEX>). The length was also related to otolith radius (R, <TEX>${\mu}m$</TEX>); L=0.0795R+0.2249 (<TEX>$r^2=0.92$</TEX>). The growth in length was represented by Gompertz growth curve; <TEX>$L_t=135{\exp}\{-{\exp}[0.0103(t-116)</TEX><TEX>]</TEX><TEX>\}$</TEX> (<TEX>$r^2=0.83$</TEX>). The hatching date calculated from the number of daily growth increments in otoliths was between mid-December and mid-February.

Of Travertine and Time: Otolith Chemistry and Microstructure Detect Provenance and Demography of Endangered Humpback Chub in Grand Canyon, USA

We developed a geochemical atlas of the Colorado River in Grand Canyon and in its tributary, the Little Colorado River, and used it to identify provenance and habitat use by Federally Endangered humpback chub, Gila cypha. Carbon stable isotope ratios (δ13C) discriminate best between the two rivers, but fine scale analysis in otoliths requires rare, expensive instrumentation. We therefore correlated other tracers (SrSr, Ba, and Se in ratio to Ca) to δ13C that are easier to quantify in otoliths with other microchemical techniques. Although the Little Colorado River’s water chemistry varies with major storm events, at base flow or near base flow (conditions occurring 84% of the time in our study) its chemistry differs sufficiently from the mainstem to discriminate one from the other. Additionally, when fish egress from the natal Little Colorado River to the mainstem, they encounter cold water which causes the otolith daily growth increments to decrease in size markedly. Combining otolith growth increment analysis and microchemistry permitted estimation of size and age at first egress; size at first birthday was also estimated. Emigrants < 1 year old averaged 51.2 ± 4.4 (SE) days and 35.5 ± 3.6 mm at egress; older fish that had recruited to the population averaged 100 ± 7.8 days old and 51.0 ± 2.2 mm at egress, suggesting that larger, older emigrants recruit better. Back-calculated size at age 1 was unimodal and large (78.2 ± 3.3 mm) in Little Colorado caught fish but was bimodally distributed in Colorado mainstem caught fish (49.9 ± 3.6 and 79 ± 4.9 mm) suggesting that humpback chub can also rear in the mainstem. The study demonstrates the coupled usage of the two rivers by this fish and highlights the need to consider both rivers when making management decisions for humpback chub recovery.

Evaluating eelgrass site quality by the settlement, performance, and survival of a marine fish

The quantity of habitat can be defined by the distribution and abundance of organisms, but it is the quality of the habitat that may have more direct demographic consequences. Habitat quality is best assessed by determining demographic rates and the performance of the focal species residing within a habitat. Using this framework to develop a method for evaluating habitat quality among sites, we used two demographic rates (settlement and survival) and two performance measures (growth and condition) of the giant kelpfish (Heterostichus rostratus Girard) to determine whether eelgrass (Zostera marina L.) habitat quality varies spatially (i.e., site quality) within San Diego Bay, California, USA. Seven sites were selected that encompass the northern and central areas of the bay. Settlement was estimated bi-weekly from May to July 2009 with artificial seagrass units (ASUs) and standard monitoring units for the recruitment of fishes (SMURFs). Eelgrass habitat complexity (shoot height and density) was measured at each site, and three complexity treatments were replicated with ASUs in large mesocosms to estimate survival of giant kelpfish after exposure to kelp bass (Paralabrax clathratus Girard), a common predator. Growth and condition were derived from juvenile giant kelpfish collected from sites two months after the settlement period using otolith daily growth increments and total lipid content, respectively. Settlement, growth, and condition were evaluated using a multivariate analysis to provide an assessment of habitat quality among sites and a framework for which site quality can be evaluated in different marine habitats. Combined with habitat-dependent survival from predators in laboratory trials that reflected site-specific habitat attributes, sites were ranked along a gradient of habitat quality. The multivariate analysis of site quality based on demographic and performance variables was then overlaid with a similar analysis of environmental variables. Environmental variables that would serve as proxies for habitat quality were not concordant with the suite of demographic and performance variables used to differentiate site quality, suggesting that a pluralistic approach using demographic rates and individual performance is a potentially more appropriate method for evaluating habitat quality, whether among different habitats or among sites of the same habitat.

How fast can the European eel (Anguilla anguilla) larvae cross the Atlantic Ocean?

AbstractThe migration duration of European eel (Anguilla anguilla) larvae (leptocephali) from the spawning areas in the Sargasso Sea to the European continental shelf remains highly controversial, with estimates varying from 6 months to more than 2 yr. We estimated the fastest migration period and the shortest distance travelled by eel larvae by simulating Lagrangian particles released in the Sargasso Sea and by simulating a range of larval behaviours (fixed‐depth drift, vertical diurnal migration and active‐depth selection to maximize current velocity). This enabled us to compute (i) a passive drift speed, and (ii) a hypothetic swimming speed needed for European eel larvae to cross the Atlantic in 6 months (i.e., the migration duration estimated from otolith daily growth increments). Our results show that the minimum travel time for an eel larva that is passively drifting was 10 months and 3 days. Active behaviours (vertical diurnal migration and rheotaxis) paradoxically increased the migration period. We found that for leptocephali to cross the Atlantic Ocean in 6 months, they would need to swim a minimum of 3.4 body lengths per second for 8200 km. No larvae have been observed with such swimming capabilities. These results provide evidence that leptocephali cannot cross the Atlantic in 6 months.

High‐resolution isotope analysis of young alewife Alosa pseudoharengus otoliths: assessment of temporal resolution and reconstruction of habitat occupancy and thermal history

Otoliths of age 0 year alewife Alosa pseudoharengus collected in different Lake Michigan habitats were microsampled, and carbon and oxygen isotope ratios (δ18Ootolith and δ13Cotolith) of resulting microsamples were quantified. To assess the temporal resolution of the method, age and otolith growth rates were also estimated by counting otolith daily growth increments. Core and outer intra‐otolith samples averaged 36 and 23 days, respectively. Because of the accretionary nature of otolith growth, a habitat switch by a larva occurring between 0 and 18 days post‐hatch may not be recognized by this approach. Taking this temporal resolution into account, A. pseudoharengus habitat occupancy and thermal history in nearshore Lake Michigan, and a connecting drowned river‐mouth lake were documented. Comparisons between δ18Ootolith and δ13Cotolith profiles, and isotope values of Lake Michigan habitats suggested that movements by individual fish between a nearshore area of Lake Michigan proper and drowned river‐mouth lake habitats were rare. Some individuals evidently moved between habitats, and such movements occurred during different periods of ontogeny. Thermal reconstructions, based on δ18Ootolith values suggested that during early life (e.g. first month of life) young A.pseudoharengus appeared to inhabit microhabitats with temperatures greater than mean epilimnetic temperatures. This study demonstrates not only the utility of intra‐otolith geochemical analysis to describe the complexity of fish behaviour in fresh water but also identifies limitations of the present approach.

Reproduction of landlocked Aplochiton zebra Jenyns (Pisces, Galaxiidae)

Abstract – Life‐history studies comparing landlocked versus diadromous populations reveal factors associated with life‐history evolution under different scenarios. We describe several aspects of spawning and development of landlocked Aplochiton zebra in Patagonia (Argentina) based on the presence of eggs, the gonadal development, the analysis of otolith daily growth increments validated by tetracycline marking experiments, and the analysis of standard length frequencies. Among Patagonian galaxiids, A. zebra showed intermediate size and age at first maturity and high fecundity, with vitellogenic oocytes covered with short chorionic filaments. Free embryos of A. zebra were larger than those of Galaxias maculatus and Galaxias platei. This information is particularly significant for conservational purposes when we consider the reduced distribution of landlocked populations of the species and the risks imposed by salmonid introduction.

Identifying the contribution of wild and hatchery Chinook salmon (Oncorhynchus tshawytscha) to the ocean fishery using otolith microstructure as natural tags

Quantifying the contribution of wild (naturally spawned) and hatchery Chinook salmon (Oncorhynchus tshawytscha) to the mixed-stock ocean fishery is critical to understanding their relative importance to the persistence of salmon stocks. The inability to distinguish hatchery and wild salmon has inhibited the detection of declines or recoveries for many wild populations. By using Chinook salmon of known hatchery and wild origin, we established a baseline for separating these two sources using otolith microstructure. Otoliths of wild salmon contained a distinct exogenous feeding check likely reflecting an abrupt transition in food resources from maternal yolk not experienced by fish reared in hatcheries. Daily growth increments in otoliths from hatchery salmon immediately after the onset of exogenous feeding were wider and more uniform in width than those in wild fish. The discriminant function that we used to distinguish individuals reared in hatcheries or in the wild was robust between years (1999 and 2002), life history stages (juveniles and adults), and geographic regions (California, British Columbia, and Alaska) and classified fish with ~91% accuracy. Results from our mixed-stock model estimated that the contribution of wild fish was 10% ± 6%, indicating hatchery supplementation may be playing a larger role in supporting the central California coastal fishery than previously assumed.

Validation of daily otolith increments in larval and juvenile Chinese sucker, Myxocyprinus asiaticus

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.

Daily growth increment formation in otoliths of Pacific tarpon Megalops cyprinoides during metamorphosis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 312:255-263 (2006) - doi:10.3354/meps312255 Daily growth increment formation in otoliths of Pacific tarpon Megalops cyprinoides during metamorphosis H. L. Chen, W. N. Tzeng* Institute of Fisheries Science, College of Life Science, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd, Taipei, Taiwan 106, ROC *Corresponding author. Email: wnt@ccms.ntu.edu.tw ABSTRACT: The otolith microstructure of Pacific tarpon Megalops cyprinoides was examined to determine whether there were influences on the deposition of otolith daily growth increments (DGIs) during metamorphosis from leptocephalus to juvenile. Leptocephali collected in a Taiwanese estuary in August 2003 were fully grown and completed metamorphosis in approximately 10 d during rearing in environmental conditions similar to those in the wild. The metamorphic process was divided into Stages II and III based on temporal changes in external morphology, otolith growth rate, and Sr/Ca ratio. The otolith increment width (OIW) was comparatively small for the leptocephalus (Stage I) before the experiment, increased rapidly at Stage II, and reached a maximum at the beginning of Stage III. In contrast, the otolith Sr/Ca ratio decreased sharply after Stage II. Metamorphosis was accompanied by a breakdown of Sr-rich sulfated glycosaminoglycans (GAGs) in the body, a change of body organization, body length shrinkage, and otolith rapid growth; growth increments in otoliths were deposited daily throughout. The metamorphic process of the Pacific tarpon leptocephalus is analogous to that of the anguillid eel, and the mechanism of otolith DGI deposition during metamorphosis may be similar. KEY WORDS: Elopiformes · Pacific tarpon · Megalops cyprinoides · Leptocephalus · Morphology · Metamorphosis · Otolith · Daily growth increments · Sr/Ca ratio Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 312. Online publication date: April 24, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Larval development and growth of the European hake &lt;i&gt;Merluccius merluccius&lt;/i&gt; in the northwestern Mediterranean

The larval growth and development of the European hake, Merluccius merluccius , was studied from field larvae. Larvae were collected in the northwestern Mediterranean on three cruises carried out during the peak spawning months (November 1998, September 1999 and November 1999). Like other species of the genus, these larvae are characterised by a well-developed anterior part of the body, head and trunk region. Nevertheless, yolk sac larvae are much more slender than larvae at notochordal flexion stages. In the present study we analysed the allometric relationships between several body measurements and body length. This is the first attempt to infer larval growth of Merluccius merluccius by means of sagittal otolith analysis. Our results show the change in the otolith shape from a lenticular otolith in early larvae to an almond-shaped otolith in larger larvae. Otolith diameter showed a power relation with larval size, with no significant differences between seasons. In spite of the sea surface temperature differences between the three periods of larval collection, the early growth estimates showed no significant differences. This was explained by the similarity in the temperature at the depths at which the larvae are located. Absolute growth rates in length were estimated by relating daily growth increments in otoliths and larval size (standard length). When using the whole larval size range the values obtained were similar to those found for other Merluccius species. Nevertheless, the present data evidenced that growth for larvae younger than 12 days is very low, showing a significant increase thereafter. This indicates that length is probably not the best parameter for describing the growth of hake larvae in the first days of life, as allometric analysis suggested.