Age and early life history of juvenile scotia sea icefish, <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis>, from Elephant and the South Shetland Islands

The otolith microstructure of juvenile Scotia Sea icefish (Chaenocephalus aceratus) was analyzed from samples collected around Elephant and South Shetland Islands, with the aim to validate previous annual ageing and to give new insight into its early life history timings. Fish were caught by bottom trawl fishing conducted on the continental shelf between 100 and 500 m depth. To determine the timing and position of the first annulus on sagittal otoliths, microincrements were counted on juvenile otoliths previously aged 1+ year old by counting annuli in sectioned otolith. Assuming that microincrements were laid down daily, age ranged from 406 to 578 days in fish measuring 13–19 cm TL, thus corroborating previous results. The relationship between fish size and otolith size/weight was estimated using the least square linear regression method. The relationship between age and otolith size was also estimated to determine the otolith length in 1-year old fish, which was approximately 1.58 mm. In all samples the otolith core was characterized by an evident strong check, assumed to be laid down at the beginning of exogenous feeding of yolk sac larvae. The yolk sac duration estimated from hatch to the first feeding check was longer than other channichthyids, lasting 29–45 days. Hatching dates were backcalculated from the date of capture using the age estimates, indicating C. aceratus sampled off Elephant and South Shetland Islands hatched over a long period lasting from July to December, with a peak in November. As a result, the potential larval dispersion driven by local oceanographic features is discussed.     

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.     

Life history of the Hawaiian blackhead triplefin, <Emphasis Type="Italic">Enneapterygius atriceps</Emphasis>(Blennioidei,Tripterygiidae)

Synopsis We described aspects of the life history of the small, cryptic, triplefin blenny, Enneapterygius atriceps, collected from the mouth of Kaneohe Bay, Oahu, Hawaii. We examined otolith microstructure to construct a von Bertalanffy growth curve, described a length–weight relationship, performed a detailed dietary analysis, used standard histological techniques to determine size at maturity and reproductive patterns, determined batch fecundity, and used an index of gonadal development to examine spawning seasonality. Enneapterygius atriceps is a remarkably short-lived species with low fecundity and a short, well-defined breeding season. Dietary analysis suggests this fish lives and feeds around the bases of dead coral heads. This study generated the first otolith-based growth curve for any member of the Tripterygiidae.     

Length–weight and length–length relationships of three fish species from the Yarlung Zangbo River in Tibet,China

Length–weight relationships and length–length were evaluated for three fish species (Schizopygopsis younghusbandi Regan, 1905; Ptychobarbus dipogon Regan, 1905 and Oxygymnocypris stewartii Lloyd, 1908) from the Yarlung Zangbo River in Tibet. Specimens were captured monthly using floating gillnets (mesh size 7.5 cm), bottom gillnets (mesh size 6.5 cm), and trap nets (mesh size 1.5 mm) from August 2008 to August 2009, March to August 2012, and March to April 2013. Regression coefficient (b) values of length–weight relationships (LWRs) ranged from 3.045 for P. dipogon to 3.193 for O. stewartii, whereas the a values ranged from 0.0040 to 0.0168 for O. stewartii and P. dipogon, respectively.     

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.     

Validation of daily microincrement deposition in otoliths of juvenile and adult Peruvian anchovy Engraulis ringens

Wild adult specimens of the Peruvian anchovy Engraulis ringens were captured and reared to validate the daily periodicity of otolith microincrement formation. The postcapture stress generated spontaneous spawning, making it possible to conduct a rearing trial on larvae first in an artificial nutrient‐enriched system (ANES) for 52 days followed by an artificial feeding regime in a culture tank until day 115 post‐hatch. Microincrements of the sagittal otoliths of sacrificed juveniles [mean ± s.d. total length (L_T) = 5·13 ± 0·37 cm, range 5–6 cm; c.v. = 7·5%] showed very distinct light and dark zones. The slope of the relationship between the total number of increments after the hatch check and days elapsed after hatching was not significantly different from 1. The transfer from ANES to the artificial feeding regime induced a mark in the sagittal otoliths. The number of microincrements after this induced mark coincided with the number of days elapsed after the transfer date. In parallel experiments, adult E. ringens (mean ± s.d. L_T = 14·92 ± 0·55 cm, range 13–16 cm) were exposed to one of two fluorescent marking immersion treatments with either alizarin red S (ARS; 25 mg l^?1 per 6 h) or oxytetracycline hydrochloride (OTC; 200 mg l^?1 per 10 h). The microincrements between fluorescent bands were distinct, ranging from 0·89 to 2·75 µm (mean ± s.d. =1·43 ± 0·28 µm; c.v. = 32%) and from 0·71 to 2·89 µm (1·53 ± 0·27 µm; c.v. = 35%) for ARS and OTC, respectively. The relationship between the number of microincrements between marks and the number of elapsed days for ARS and OCT treatments indicated that there was a significant correspondence between the number of increases observed and the number of days. Hence, daily microincrements of otoliths of E. ringens are likely to be formed in juveniles and adults under natural conditions.     

Common otolith microstructure related to key early life‐history events in flatfishes identified in the larvae and juveniles of cresthead flounder Pseudopleuronectes schrenki

Otolith microstructure of reared and wild cresthead flounder Pseudopleuronectes schrenki larvae and juveniles was used to investigate the daily periodicity of ring formation, morphological change and unique otolith structure related to important life events. By comparing microstructural features of P. schrenki with those reported for other flatfish species, it was shown that there may be microstructural features that are common to all flatfishes. In the sagittae and lapillus, a check (a distinct ring) was formed in the centre of otoliths at c. 6 days post hatching, and the daily formation of rings observed outside the check was confirmed. During metamorphosis, accessory primordia (AP) of otolith growth were formed on the outer edge of the sagittae, and the shape of the sagittae became more complex. No AP was formed on the lapilli, however, and otolith rings were concentrically formed throughout the larval and juvenile (≤51·6 mm standard length, L_S) stages. It is proposed, therefore, that lapilli are more appropriate than sagittae for analysis throughout the larval and juvenile (≤51·6 mm L_S) stages. During metamorphosis, unique rings that are relatively wide and show weak contrast are formed on lapilli (metamorphosing zone, MZ). Hence, the duration of metamorphosis, larval duration and the days of juvenile life can be estimated by the number of rings within the MZ, using rings from the check to outermost ring of the MZ, and that of rings formed outside MZ, respectively. The formation of AP on sagittae as well as the absence of AP, bilateral asymmetry and the formation of a unique structure during metamorphosis on lapilli have also been reported for other flatfishes.     

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.     

Age and growth of Benthosema pterotum (Alcock, 1890) (Myctophidae) in the Oman Sea

Juvenile and adult specimens of Benthosema pterotum (skinnycheek lanternfish) were collected during several surveys conducted on the Iranian continental shelf of the Oman Sea. Age was estimated by enumeration of growth increments in sagittae otolith sections on the assumption of their daily deposition. Three distinct growth zones in otolith microstructure (central, middle, and external) were defined. These three zones presumably represent increments deposited during successive life history stages, characterized by a different migratory behavior and depth occurrence. The number of increments in the central zone of the B. pterotum otolith (26.8 on average) was thus far one of the lowest in myctophid species studied. A negative correlation between the number of increments in the central and middle zones was observed. This might suggest a functional relation between these two periods of early life history, when fewer larvae in the epipelagic layers may be compensated by a longer non‐migratory behavior of metamorphosis larvae and early juveniles. The maximum number of growth increments in B. pterotum otoliths, i.e. 315, indicated a short lifespan of probably <1 year. The relationship between otolith length and standard length was described by linear regression model (r² = 0.902), and between the body length and weight as an isometric growth in 274 juvenile and adult specimens (r² = 0.922). The growth model estimated only for juveniles and adults was curvilinear (SL = 1.150 × Age^0.616; r² = 0.868). Back‐calculated hatch dates might suggest a spawning season of B. pterotum from May to September, but due to the limited number of investigated specimens a prolonged spawning cannot be excluded. Further trials are needed to measure the population parameter dynamics.     

Age and growth of the spotted goatfish, Pseudupeneus maculatus (Bloch, 1793) in Brazil, validated through marginal increment and oxytetracycline dyes in the sagittae

A sample composed of 4973 specimens of the spotted goatfish, Pseudupeneus maculatus (4.5–29.2 cm fork length) was collected off northeastern Brazil from 1999 to 2002. Sagittae (398) were analyzed for age and growth estimation using both annuli and microincrements. For the first approach, the mean monthly marginal increment ratio analysis suggested that one band is formed annually from May to June. With the microincrements analysis, 15 specimens were reared (3–71 days) for validation of periodicity using oxytetracycline. Fluorescent dyes were observed in 10 specimens (7.5–16.9 cm). After testing, one microincrement was found to form daily. Otolith sections were polished and analyzed using a light microscope (100–1200× magnifications). Individuals larger than 22.6 cm (4 years) showed heavily overlaid increments on the otolith edge, which hampered the counts. There was agreement on the size from counts on an annual and daily basis. The von Bertalanffy function provided the following parameters: L_∞ = 33.23 cm; K = 0.265; t₀ = 0.0883 year. The sample was composed of 0⁺ to >5‐year‐old specimens. Age at first maturity was 3.6 years (20 cm), whereas the recruitment age for fisheries was 3.9 years. Juveniles represented about half of the catch (48.7%), which may have implications for population equilibrium.     

Growth acceleration,behaviour and otolith check marks associated with sex change in the wrasse <Emphasis Type="Italic">Halichoeres miniatus</Emphasis>

In protogynous sex-changing fishes, females are expected to compete for the opportunity to change sex following the loss of a dominant male and may exhibit growth and behavioural traits that help them maintain their dominant status after sex change. A male removal experiment was used to examine changes in female growth and behaviour associated with sex change in the haremic wrasse Halichoeres miniatus and to test whether any changes in growth associated with sex change were recorded in otolith microstructure. Dominant females began displaying male-characteristic behaviour almost immediately after the harem male was removed. The frequency of interactions between females increased following male removal. In contrast, feeding frequency of females decreased. The largest one to three females in each social group changed sex following male removal and exhibited an increase in growth associated with sex change. Sex changers grew more than twice as fast as non-sex changers during the experimental period. This growth acceleration may enable new sex-changed males to rapidly reach a size where they can defend the remaining harem from other males. An optical discontinuity (check mark) was present in the otoliths of sex-changed fish, and otolith accretion rate increased significantly after the check mark, corresponding with the increased growth rate of sex-changing females. Wild caught males, but not females, exhibited an analogous check mark in their otoliths and similar increases in otolith increment widths after the check. This indicates that an increase in growth rate is a regular feature of sex-change dynamics of H. miniatus. Communicated by Environment Editor Prof. Rob van Woesik     

Age determination of the Antarctic fishes Champsocephalus gunnari and Notothenia rossii marmorata from South Georgia

Summary Investigations were performed on otoliths from Champsocephalus gunnari and Notothenia rossii marmorata as part of an effort to study the population dynamics of Antarctic fishes. Examination of otoliths by scanning electron microscope (SEM) revealed internal microincrements which were similar to daily increments described for other fish species. No easily identifiable annuli could be discerned and fishes were aged by counting microincrements. Multiple regression analyses relating age to otolith morphometrics and fish size, provided a simpler ageing method. It was determined with these techniques that C. gunnari grew to 50 cm in 15 yrs and N. rossii marmorata grew to 50 cm in 6.5 yrs. The lack of larger-sized individuals for N. rossii marmorata may be indicative of recent overfishing with only the younger age groups remaining. It appears that length-at-age data determined on a yearly basis, could provide valuable scientific and management information for these species.     

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.     

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.     

Otolith morphology, microstructure and ageing in the hedgehog seahorse, Hippocampus spinosissimus (Weber, 1913)

The life history characteristics of many species of seahorse, including the hedgehog seahorse Hippocampus spinosissimus, make them sensitive to exploitation. Consequently, proper management tools must be employed; these are often based on reliable ageing. The aim of the present study was to evaluate the possibility of using otoliths for ageing hedgehog seahorses from Vietnam. Asteriscus, lapillus and sagitta all showed moderate to strong correlations between fish standard length (SL), otolith length and number of increments in seahorses between 83 and 188 mm SL. There were no annual or seasonal marks in any of the three otolith pairs observed using dissecting or light microscopy, and only asteriscus revealed microincrements under light microscopy. The number of increments ranged between 71 and 137. A full trajectory of lapillar microincrements was only visible when using scanning electron microscopy, and then only in two of the examined individuals (88 and 115 increments). A validation experiment showed that the number of increments in the asterisci did not correspond to the age of seahorses bred and reared for 717 and 868 days. Furthermore, a second validation study using Alizarine Complexone (ALZ) otolith marking did not reveal any increments peripheral to the ALZ mark 30 days after marking. The conclusion of the study was that otoliths do not at present provide a reliable tool for estimating age in adult hedgehog seahorses, and therefore other tools have to be employed to improve their management.     

Ontogenetic development,allometric growth patterns,and daily increment validation of larvae and juvenile Culter alburnus

Fish ontogeny, allometric growth patterns, and otolith microstructure are fundamental in aquaculture and essential for understanding the early-life ecology of fish. Culter alburnus is a commercially important fish species and an excellent breeding target for aquaculture. In this study, newly hatched C. alburnus larvae were reared to the juvenile stage in a hatchery. Three days post hatch, the eyes, mouth, and intestine had developed, and the larval yolk sac had been completely absorbed. Fin rays started to differentiate in the flexion stage and were fully developed by the postflexion stage. Pigmentations were well developed in the juveniles. Culter alburnus larvae were characterized by 39–43 myomeres and 23–25 anal fin rays, swim bladder shape, and pigmentation. Head length, height, and musculature height showed positive allometric growth patterns, suggesting that head and trunk growth was prioritized. Positive allometric growth of the tail was simultaneous with the formation of fins, suggesting that swimming mode transformation, diet changes, and habitat shifts occurred after the start of the postflexion stage. Otolith growth increments in both the sagittae and lapilli were deposited daily, with the first increment formed on day 1 on the sagittae and day 4 of yolk sac absorption on the lapilli. Increments were thin and faint during the early developmental stage, gradually increasing to reach the broadest widths and the strongest contrast at the postflexion stage, which may be related to habitat shifts. This information will assist in the breeding and hatchery production of C. alburnus and establish suitable methods for analyzing this species’ spatiotemporal distributions and early-life traits.

     

Microprobe analyses of anadromous Arctic charr, Salvelinus alpinus, otoliths to infer life history migration events

Otoliths of Arctic charr, Salvelinus alpinus, from north Labrador were examined to gather life history information pertinent to anadromous migrations. Wavelength dispersive electron microprobe measurements confirm the presence of strontium in otolith tissue. Trace element analyses of charr otoliths imply that otolith strontium/calcium concentration ratios are related to external environmental factors with salinity having a great influence. Otoliths clearly record habitat shifts consistent with migration across major salinity boundaries. Most charr first migrate to sea following at least 2 years in freshwater. Generally, when anadromy begins, it continues annually. Robust relationships in otolith chemistry, combined with macrostructure patterns in field-captured specimens, provide time-series data describing individual migrational histories. Validation studies are still required in order to couple information contained within daily increments with chemical analyses to infer additional temporal events in diadromous migrations. Received: 6 November 1996 / Accepted: 18 May 1997     

Variation in migratory history of Dolly Varden in a stream with an artificial dam in the Shiretoko Peninsula,Hokkaido, Japan

The variation of migration patterns in Dolly Varden Salvelinus malma in a stream with an artificial dam (erosion-control-dam) in the Shiretoko Peninsula, Hokkaido Island, Japan, at the southernmost part of its distribution, was examined by otolith Sr:Ca ratio analysis. All specimens from the above-dam area showed consistently low Sr:Ca ratios (<5.0 × 10⁻³) throughout the otolith. In contrast, many specimens from the below-dam area had higher ratios (>5.0 × 10⁻³) throughout the otolith or only at the outer part than do those from the above-dam area. This higher ratio is probably due to salinity effects. Specimen from the below-dam area could be divided into three types: (1) Consistently low Sr:Ca ratios throughout the otolith, being freshwater residents. (2) Low Sr:Ca ratios around the inner part of the otolith, and thereafter higher ratios toward the outer part, being typically anadromous. (3) Relatively higher Sr:Ca ratios throughout many or in some parts of the otolith, indicating that these have migrated from the freshwater to brackish water or seawater from the early life stage. These findings suggest that Dolly Varden has a high degree of plasticity in its migratory behavior.     

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.     

Early ontogeny of the mackerel icefish, Champsocephalus gunnari, in the southern Scotia Arc

During the early ontogeny of fishes, the timing and duration of key events such as larval hatching and the switch from endogenous to exogenous feeding largely determine the offspring viability and survival. The aim of the present study was to investigate the life history traits of the early larvae of the mackerel icefish, Champsocephalus gunnari, collected in summer south of the South Shetland Islands in the Bransfield Strait and north of Elephant Island. Through the analysis of sagittal otolith microstructure, we assessed the timing and duration of egg incubation, larval hatching, first exogenous feeding, rate of yolk resorption and body growth rate. Compared to populations living further north (i.e. around South Georgia and Kerguelen Islands), mackerel icefish in the southern Scotia Arc exhibits longer egg incubation (lasting 90–120 days from winter to summer) and delayed hatching time spread over a relatively short period lasting 26 days between January and February. The first exogenous feeding takes place between 13 and 24 days after hatching still in the presence of the yolk-sac, indicating a prolonged mixed feeding afterward. The specific growth rate or daily percentage change in size (G) was 1.9 % SL day^?1, corresponding to a daily growth rate at mean size of 0.31 mm day^?1. While showing significant differences in early life history traits across their geographical distribution, C. gunnari populations share a common strategy, spawning a small number of large eggs that hatch in relatively large-sized larvae, at a time which may be independent of the timing of pack-ice retreat and onset of the production cycle.