Otoliths Of Eels Research Articles

Effects of salinity and ontogenetic movements on strontium:calcium ratios in the otoliths of the Japanese eel, Anguilla japonica Temminck and Schlegel

To study the mechanism of Sr incorporation into otoliths of the Japanese eel, Anguilla japonica, a total of 100 elvers collected from an estuary were reared in the laboratory at salinities of 0, 10, 25 and 35%. for approximately seven months. The elvers grew from 56 mm TL to 100–300 mm TL. Twenty elvers were randomly selected and the Ca and Sr concentrations of their otoliths were analyzed from the primordium to the edge, using an electron microprobe equipped with a four-channel wavelength-dispersive spectrometer. Sr Ca ratios in the otoliths of eels reared in various salinities were much lower than the ratio of 15 × 10 −3 observed in elvers about one month before they arrived at the estuary. The irreversibility of Sr Ca ratios at 35%. salinity in this experiment indicated that the drastic change of the Sr Ca ratios in otoliths of elvers was not due to the reduction of salinity in the coastal waters, but more likely to the development from leptocephalus to glass eel. The mean Sr Ca ratios in the new increments of the otoliths of eels during the rearing period were highly correlated with salinity ( S), [ Sr Ca ] × 10 3 = 3.797 + 0.14S ( n = 20, r = 0.77), which can be used to predict elver movements and habitat utilization rates.

Microstructural growth in otoliths of conger eel (Conger myriaster) leptocephali during the metamorphic stage

Otolith growth during metamorphosis and some aspects of the early life history of conger eel (Conger myriaster) were determined as indicated from microstructure in otoliths of the leptocephali collected from Cheonsu Bay, Korea during May and June 1988. The leptocephali occurred from early May to late June in the study area. Larvae collected in early May were in the late leptocephalus stage, and the proportion of the metamorphosing leptocephali increased over time. Otoliths in the late leptocephalus stage showed a translucent zone only. Although the fish did not feed and the body length diminished during metamorphosis, the otolith continued to grow and, consequently, the opaque zone was formed outside the translucent zone. The inner translucent zone can be considered a leptocephalus zone, and the outer opaque zone a metamorphic zone. Assuming that the growth increments were deposited daily from hatching, the conger eel can be considered to have hatched between September and February. The number of increments in the inner hyaline zone ranged from 124 to 239, and was assumed to represent the number of days from hatching to the onset of metamorphosis. The duration of metamorphosis was estimated as 51 to 75 d based on the number of increments in the opaque zone at the end of the metamorphic stage.

Longevity of longfinned eels Anguilla dieffenbachii in a New Zealand high country lake

AbstractA sample of 146 longfinned eels (Anguilla dieffenbachii), ranging in length from 231–1203 mm, was collected from Lake Rotoiti, Nelson Lakes National Park, New Zealand. Otoliths (n= 114) of eels were difficult to read, mainly due to the considerable age (maximum age 106 years). Growth rate was slow and linear, averaging 9 mm. year−1. These are the slowest growth rate and maximum age from any study of Anguilla spp. to date. Lakes within National Parks provide the largest commercially unfished waters within New Zealand and hence provide reserve breeding stocks of longfinned eels; however, the average generation time of 93 years for female eels from Lake Rotoiti implies that stock management should be conservative.

Scanning electron microscopic analysis of annulus microstructure in otolith of European eel, Anguilla anguilla

To validate the yearly periodicity of annulus formation in the otolith of the eel, the structure of annuli in otoliths of the European eel, Anguilla anguilla, stocked for 7 and 12 years in Lake Ommen on the east coast of southern Sweden, was examined. The population was stocked from elvers imported both from France (Bay of Biscay) in April 1979 and England (River Severn) in March–April 1984. The microstructure of an annulus consisted of single, double and/or composite tings depending on the location in the otolith. The counts of annuli in otoliths of these eels were approximately consistent with the expected age. However, supernumerary false annuli and/or annulus underestimation frequently occurred. The methodology for annulus discrimination with light and scanning electron microscopes is described.

Age and growth of longfinned eels (Anguilla dieffenbachii) in pastoral and forested streams in the Waikato River basin, and in two hydroelectric lakes in the North Island, New Zealand

Abstract Growth rates of New Zealand endemic longfinned eels (Anguilla dieffenbachii) from streams in pasture and indigenous forest, and from two hydroelectric lakes (Lakes Karapiro and Matahina), were estimated by otolith examination. Habitat‐specific growth was further investigated with measurement of widths of annual bands in otoliths. Longfinned eels 170–1095 mm in length ranged between 4 and 60 years old (N = 252). Eels in pastoral streams grew faster (mean annual length increment ±95% CL = 24 ± 3 mm to 36 ± 7 mm) than eels in streams in indigenous forest (annual length increment 12 ± 2 mm to 15 ± 3 mm). Eels from the hydro‐electric lakes had growth rates (annual length increments 19 ± 4 and 19 + 7 mm) similar to eels from pastoral streams. Otoliths of most eels showed annual band widths that indicated growth in several different habitats, corresponding to growth during upstream migration, and limited movement among adult habitats. Estimated age at marketable size (220 g) ranged between 7 and 26 year...

Measurements on ground or sectioned otoliths: possibilities of bias

Back‐calculation usually requires measurements of growth marks revealed on otoliths by specific preparations. The standardization of the grinding (or sectioning) plane is necessary, but difficult, especially along the antero‐posterior axis. In order to show the importance of the grinding plane, tetracycline labelling of eel otoliths (Anguilla anguilla L.) has been used. This marking has a calcio‐traumatic effect on otoliths, which can be revealed with staining techniques. Unless the grinding plane is incorrect, the tetracycline labelling and the staining of the ground surface are then superposed.

The crystalline ultrastructure of otoliths of the eel (A. anguilla L. 1758)

The ultrastructure of the organic and the mineral components of eel (Anguilla anguilla L. 1758) otoliths was studied using sections through the nucleus and observed by scanning electron microscopy. The otoliths were composed of crystalline material (aragonite) running radially from the centre to the edge. Structural discontinuities were described: seasonal rings, checks and daily growth increments.

Growth history and age at recruitment of European glass eels (Anguilla anguilla) as revealed by otolith microstructure

The growth history and age at recruitment of Anguilla anguilla Linnaeus, 1758 were studied, based on growth increments in sagittal otoliths of glass eels and elvers collected from the eastern Atlantic coast in 1989 and in 1990. The maximum otolith radius varied with pigmentation stage. Deposition of the transition ring was complete at Stage VIA0. The size of the leptocephalus growth zone varied as a function of site, increasing from south to north. The oceanic migration of the leptocephali required less than one year.

Reading otoliths of eels, Anguilla anguilla (L.), of known age from Kolderveen, The Netherlands

. In this study we aged eels, Anguilla anguilla (L.), from a pond in the Netherlands stocked with elvers in 1966. Yellow eels were sampled from the pond in 1981. Burning and cracking the otoliths of these eels gave the expected age (15 years) in 27% of the cases, with a mean estimated age of 12·3 years. As some immigration of young eels into the pond must have occurred after stocking, the percentage of correctly determined specimens is even higher. Clearing the otoliths in ethanol was not a good method for these eels, giving a mean estimated age of 7·7 years and no age over 10 years. The use of the burning and cracking technique is recommended.

Age determination and growth of eel, Anguilla anguilla (L.), in lake Fertő Hungary

Ground and polished otolith sections, 0.2 mm thick, were produced from both sagittae of each fish, and repeated readings of the growth marks resulted in more accurate estimates of fish age. Supernumary zone formation in eel otoliths was a common phenomenon. The growth in length of the eels was accurately described by Bertalanffy's model using back-calculated lengths. Values of L ∞ = 1459 mm, K = 0.058 and t 0 = −0.869 years were determined. Mean incremental growth was calculated as 5–9 cm per year, showing that length increases rapidly with age. However, the growth of the eel population in Lake Fertő has become stunted, probably due to overstocking since 1975.

An improved grinding technique for examining fish otoliths for age and growth studies with special consideration of the eel, Anguilla anguilla L.

. A simple technique of grinding eel otoliths (sagittae) for age/growth studies is described. On thin, polished otolith layers the annual growth rings, as well as supernumerary zones formed in fresh water, could be easily distinguished. The described equipment and grinding procedure gave good results on permanent preparations, allowing repeated age-readings. The procedure appears to be applicable to other fish species as well.

Age determination of eels, Anguilla anguilla (L): comparison of field data with otolith ring patterns

Otoliths of eels recaptured up to 5 years after tagging were used for comparative work on the determination of annual ring patterns. It was possible to locate false annuli caused by the tagging procedure and subsequently to define annual rings in otoliths within the known period between first tagging and final catch. This determination gave an estimate of the size of the annual zones. Growth depression caused by tagging could be shown in cross sections of otoliths. Well defined annulus patterns in micrographs of otoliths from tagged eels were compared with otoliths from untagged eels. This comparison allowed a dimensional calibration of the ageing method and the recognition of misleading additional rings. Mean annual length increments of 47.88 mm and Lx, of 123.3 mm were determined.

Distribution, abundance, growth and food of freshwater eels (Anguilla spp.) in the Douglas River, Tasmania

Population structure, growth and diet of the freshwater eels A. reinhardtii Steindachner and A. australis australis Richardson were studied in the Douglas River, eastern Tasmania. Fish population structure was assessed by electrofishing, and efficiency of capture was determined for 'eels' and 'other fish'. The other fishes encountered during quantitative sampling were the native Galaxias maculatus (Jenyns), G. truttaceus Valenciennes, Pseudaphritis urvillii (Cuvier & Valenciennes), Favonigobius tamarensis Johnston, and the introduced brown trout, Salmo trutta L. A. reinhardtii dominated fish biomass in the lower freshwater reaches; an estimate of 115 gm-2, recorded at the lowest sampling site, is the highest eel biomass recorded in a Tasmanian stream. A decline in the number and weight of A. reinhardtii with increased distance from the sea was related to avoidance of low water temperatures in winter and/or a parallel decline in abundance of suitable forage fish. Measurements of marginal growth increments in burnt eel otoliths indicated the formation of annual growth rings in both species. Age groups 0: 1 and 2 of A. reinhardtii were poorly represented; this was attributed to a residence in the estuary or deep pools of the river, rather than to failure in recruitment. Growth rate of A. a. australis was slower than that of A. reinhardtii. The diet of both eel species changed significantly with size. The diet of larger individuals of A. reinhardtii had an increased dependence on fish; fish were not recorded in the diet of A. a. australis. The diet of small (less than 20 cm) eels was similar for both species, a feature that may lead to direct competition during periods of low summer flows.

An improved technique for preparing eel otoliths for aging

Abstract The sagittal otoliths are removed from the eel and heated in a bunsen flame. Otolith fragments are embedded in clear silicone rubber sealant with the reading surface pressed against the surface of a microscope slide. The otoliths can then be read through the inverted slide under a binocular microscope using reflected light.

The problem of the supernumary zones in otoliths of the European eel ( Anguilla Anguilla (Linnaeus, 1758)); a suggestion to cope with it

The study of otoliths of eels of known age has irrefutably proved that more than one growth zone per year may be discerned. Consequently, in order to obtain a correct eel age determination, the need exists to distinguish between summer growth stops and winter growth stops. As the human eye in direct observation is apparently unfit for this purpose, one is compelled to resort to instruments. A tentative solution to solve this problem is offered.

A technique for examining eel otoliths

This note describes the use of a rib‐cutting forceps in extracting the otoliths and a method of preparing permanently mounted specimens of burned otoliths.

The American Eel (Anguilla rostrata) in Eastern Lake Ontario

The life history of eels in Lake Ontario was studied by measuring, tagging, and releasing about 1500 individuals between 1958 and 1966. The smallest eels captured were from 295 to 318 mm long. Presumably they entered the lake at about age III–IV at lengths of 200–300 mm. Otoliths of eels from the lake showed a range in age between IV and XVIII, while those of smaller eels from the Ottawa River ranged between age II and IX. The length–weight regressions showed two distinct growth phases: one from about 480 mm to 790 mm, the other from about 830 mm to 1080 mm. Growth of the orbital diameter, interorbital distance, and pectoral fin length in relation to total length was not obviously related to sexual maturity. Eels that emigrated from the lake had a greater weight–length ratio than those that remained in the lake for another year. Of 917 tagged eels transplanted within Lake Ontario, 28 were recaptured near and 18 recaptured far from the original capture site. Although the results are inconclusive, there is a suggestion that eels have home territories within the lake.

OTOLITHS OF LARGE EELS FROM THE RHINE

Journal of the Royal Microscopical SocietyVolume 47, Issue 3 p. 250-252 OTOLITHS OF LARGE EELS FROM THE RHINE A. GANDOLFI HORNYOLD F.R.M.S., F.Z.S., A. GANDOLFI HORNYOLD F.R.M.S., F.Z.S.Search for more papers by this author A. GANDOLFI HORNYOLD F.R.M.S., F.Z.S., A. GANDOLFI HORNYOLD F.R.M.S., F.Z.S.Search for more papers by this author First published: September 1927 https://doi.org/10.1111/j.1365-2818.1927.tb01415.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume47, Issue3September 1927Pages 250-252 RelatedInformation