Otolith increment widths and somatic growth rate: the presence of a time-lag

Populations of the estuarine glass fish, Ambassis vachelli Richardson, were used to study the relationship between somatic growth and widths of daily increments in the sagittal otoliths. Variations in the somatic growth of A. vachelli were induced by a series of experimental feeding regimes which included feeding to satiation with two food sources and a starvation treatment. After 33 days of exposure to the experimental feeding regimes significant differences in the mean wet weight of individuals amongst the feeding treatments were recorded. Fishes subject to a starvation treatment showed a significant reduction in wet weight compared to the pretreatment population and the two experimental feeding regimes. No changes in lengths of fishes were recorded.
Validation techniques revealed that daily increments were laid down in the sagittal and asteriscal otoliths. Estimates of ring widths from samples of sagittal otoliths revealed significant treatment effects. The increments of fishes from the starvation treatment showed a significant decline in mean increment width relative to the feeding treatments. This difference was detected only after a 15 day period of experimental feeding. It is suggested that the gradual decline in increment width reflects the exhaustion of readily mobilized energy reserves.     

Validation of daily otolith increment formation in the larval myctophid fish Diaphus slender‐type spp.

The marginal increment growth in sagittal otoliths of the myctophid larvae Diaphus slender‐type spp. collected in the north‐eastern East China Sea was examined based on specimens collected at different times of the day. The calcification of the incremental zone began after midnight and took place throughout the day, and the discontinuous zone was formed only around midnight. These results indicate that otolith increments are formed daily.     

Growth and morphological development of sagittal otoliths of larval and early juvenile Trachurus japonicus

The daily periodicity of growth increment formation in sagittal otoliths of jack mackerel Trachurus japonicus was validated by marking otoliths with alizarin complexone (ALC). Analysis of otoliths of known‐age juveniles confirmed that the first increment formed on day 3 after hatching, and was associated with first feeding. A total of 198 specimens, ranging from 2·6 to 49·2 mm in body length (notochord length or standard length) and from 7 to 78 days in age, were collected in the East China Sea and Tosa Bay, and used to examine the association between otolith morphological development and ontogenetic development. The relationship between body length ( L ) and otolith radius ( R ) was significantly described by the linear function L  = 2·65 + 0·0425 R ( n  = 198, r ² = 0·99, P  < 0·001), indicating that somatic growth history can be reconstructed from otolith growth patterns. The otolith was primarily spherical in the preflexion larval stage, and became elongated with notochord flexion. The first secondary primordium formed at c . 25 days, during the middle postflexion stage, and was associated with metamorphosis. By c . 42 days the sagittal otolith was adult‐like in morphology, with the primary growth zone enclosed by the marginal growth zone, except in the anterior rostrum area. Thus age, growth and developmental stages were recorded in sagittal otoliths during the larval and early juvenile stages of jack mackerel.     

Larval duration of the lionfish, <Emphasis Type="Italic">Pterois volitans</Emphasis> along the Bahamian Archipelago

Larval duration of the non-native Indo-Pacific lionfish was estimated from samples collected along the Bahamian Archipelago using sagittal otoliths. Settlement marks, characterized by daily growth increments with reduced coloration, less definitive margins, and a re-orientation of the growth axes and otolith shape, were determined for 28 individuals. Settlement age was between 20 and 35 days with a mean of 26.2 days. Comparisons of settlement age to other littoral and reef fish species suggest that lionfish settlement age is moderate to relatively low. Lionfish pelagic larval duration is apparently sufficient to allow their rapid establishment and wide geographic range in the western Atlantic and Caribbean.     

Daily increments on the otoliths of larval and juvenile Coregonus spp., and their modification by environmental factors

The sagittal otoliths of pre- and posthatch embryos, larval, and juvenile coregonids (Coregonus spp.) were examined for growth increments. Under laboratory conditions, a check is formed on the day of hatching and subsequently one growth increment per day is deposited during at least 265 days. Under the experimental conditions of this study, the age of young coregonids can therefore be determined with high accuracy.In starving larvae, both increment width and ring contrast decrease during the first 10 days after hatching until daily increments are no longer recognizable. A change from one diet to another, alteration of the water temperature, or a short starvation period lead to the formation of characteristic ring patterns which appear on the otoliths within 1 to 3 days. These patterns are highly reproducible among all specimens of each treatment group and can therefore be used as intrinsic marks. They could be applied to hatchery-reared coregonids, thus providing a basis for judging the efficacy of stocking operations.     

The reproduction, age and growth of the spotted rockling

Biology of the Macaronesian endemic rockling Gaidropsarus guttatus was studied in the Azores. The overall sex ratio from the samples was highly in favour of females (1 : 6·33). The growth parameters were L _∞ = 24·23, k  = 1·219 and t ₀ = −0·059. Fish matured at 15 cm L _T and the spawning season was strongly clustered in April.     

An evaluation of the otolith characteristics of Conger conger during metamorphosis

A sample of 20 metamorphosing conger eel Conger conger leptocephali were collected from the Minho River, Portugal, in February 1999 and their sagittal otoliths were analysed by scanning electron microscopy. Four different etching agents were applied along both sagittal and frontal sections during otolith preparation to examine the microstructural growth in this species. Otolith growth increments were visible throughout the increment countable zone using all four treatments, but a permanent peripheral diffuse zone, where the daily increments were unclear, appeared on all otoliths, preventing accurate age estimation. To understand more about the nature of the diffuse zone, otoliths of 10 other metamorphosing leptocephali reared in aquaria were marked by immersion in tetracycline hydrochloride. The distance between the fluorescent marks and otolith edge, measured over a fixed period of time, was used to estimate the otolith growth rate. The application of this technique led to an anomalously high estimated otolith growth rate, probably as a result of the capture, marking and handling stress.     

The effect of host stage and temperature on selected developmental parameters of the solitary endoparasitoid Meteorus gyrator (Thun.) (Hym., Braconidae)

Abstract:  The development of the solitary endoparasitoid Meteorus gyrator was compared in the six larval stages of its host, the tomato moth Lacanobia oleracea , and at five constant temperatures. The host instar at the time of parasitism had a marked effect on the larval developmental period of the parasitoid, such that larvae derived from eggs oviposited in first instar hosts took approximately 18 days to egress, whilst those derived from eggs oviposited in sixth instar hosts took <10 days. The weight of cocoons was greatest when oviposition was into final instar hosts, where female cocoons averaged 12.8 mg, and lowest in those derived from eggs oviposited into first instars (9.2 mg). The parasitoid's larval development rate in third instar hosts increased with temperature increments in a linear fashion up to 25°C , after which development times were only marginally increased. At 10°C, the mean larval development time was approximately 90 days and pupal development 35–40 days, whilst at 25°C development times were 10–11 days for larvae and 6–7 days for the pupae. In the majority of cases, overall development times were marginally longer (<1 day) in females than in males.     

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.     

Daily growth increments in the larval otolith of the Japanese eel,Anguilla japonica

Early formation of otolith was studied on artificially hatched larvae of the Japanese eel,Anguilla japonica. Newly hatched larvae had a pair of sagittae which were flat and subelliptical with 8.3 μm in mean diameter. The diameter of the sagitta increased linearly with age. No growth increments were observed in the sagitta at hatching, while larvae which were 2, 4 and 6 days old had on average 2.1, 3.6 and 6.0 increments, respectively. The number of the increments (Y) and the age in days after hatching (X) showed a close linear relationship (Y=0.96X+ 0.06, r = 0.913, n = 40), suggesting daily deposition of sagittal increments. In 95 % of the field-caught elvers of this species, a distinct dark ring (check) with the diameter of 6–12 μm was found around the nucleus of the sagitta. This seems to be a “hatch check” deposited at hatching, since its diameter roughly agreed with that of the sagitta in the newly-hatched larvae. Possibly, the number of the increments outside the hatch check represents the age of the fish in days.     

Influence of light and temperature on daily activity patterns of three Israeli forms of Ptyodactylus (Reptilia: Gekkoninae)*

Activity of the gecko Ptyodactylus hasselquistii was recorded by Aktograph in cyclic light and temperature, continuous darkness or light with constant 30°C or cyclic temperature. The northern P. h. puiseuxi was more diurnal and the southern P. h. cf. hasselquistii more nocturnal than the common P. h. guttatus. Except in constant temperature and continuous light, activity was not randomly distributed throughout the day. The more nocturnal the animal was, the more the temperature played a role in determining its daily activity pattern.     

Growth during the early life history of the Pacific tarpon,Megalops cyprinoides

The early growth of the Pacific tarpon,Megalops cyprinoides, was studied by larval otolith analysis and rearing of larvae and juveniles in the laboratory. Morphology of the sagitta, validation of sagittal daily increments, age at the start of metamorphosis, decrement of standard length in early metamorphosis, and growth under rearing conditions are described. The sagitta of fully-grown Pacific tarpon leptocephali were transparent and circular, with regular intervals between the neighboring rings becoming wider at the onset of metamorphosis. Alizarin complexone treatment of larvae confirmed the daily formation of the sagittal rings. Metamorphosis was estimated to start about one month after hatching. After drastic shrinkage during the first several days of metamorphosis, the body length more or less stabilized for one month and then resumed rapid growth. The early growth of Pacific tarpon was divided into four phases as follows: A) leptocephalus positive growth phase; B) leptocephalus negative growth phase; C) sluggish growth phase; and D) juvenile growth phase.     

Otolith microstructure during the pelagic, settlement and benthic phases in burbot

During the pelagic larval phase of burbot Lota lota L., the pattern of otolith increments changes, showing three, clearly distinguishable growth sectors: a first sector with faint increments, difficult to enumerate, comprising an average (±S.D.) of 17˙5±6˙7 increments, a second sector with distinct increments comprising an average of 33˙1±7˙6 increments and a third sector where increments again become faint and difficult to enumerate. Laboratory experiments conducted in parallel to the field investigation showed that settlement occurs after the formation of this third, faint sector and is marked by the formation of numerous accessory growth centres within the range of three to five daily increments. There was a strong linear relationship between sagittal width and total length of the burbot (r²=0˙928) over the range examined. Significantly different growth rates were calculated for the three otolith sectors (faint, distinct, faint) in burbot larvae, indicating large environmental changes during their pelagic larval phase in Lake Constance. These results suggest that inshore migration of burbot larvae does not take place in the warm epilimnetic surface waters but via an alternative pathway, the cold hypolimnion or profundal zone.     

Age, Growth, and Sexual Development in the Self-fertilizing Hermaphroditic Fish Rivulus marmoratus

We studied age, growth, and sexual development in the early life intervals of the self-fertilizing mangrove killi-fish, Rivulus marmoratus. Newly hatched (day 0) individuals had sagittal otoliths of 60m radius, with about 30 increments. Sequential sampling until about day 60 after hatching yielded otoliths with the number of increments outside the 60m radius equal to the daily age of the fish. Alizarin complexone marking of otoliths also confirmed the increments were daily, and demonstrated the applicability of this technique to field studies for capture-mark-recapture, or age and growth estimates. Individuals fed a restricted amount of food formed fewer daily otolith growth increments than fish fed to satiation each day. Using histological analysis for identifying gonad morphogenesis, we found no correlation between gonadal development and external appearance (caudal ocellus, orange fin colouration) in young fish of known ages. The caudal ocellus was not present until 9mm total length, and developed thereafter. Of 136 individuals examined, fish less than 17.2mm total length (TL, n = 124) were females. Testicular tissue first appeared among individuals 17–18mm TL (n = 3), while some individuals greater than 18mm TL (n = 8) were functional hermaphrodites. The single male in our study was relatively of small body size (9.6mm, day 37) with a distinct caudal ocellus, indicating that it is presumably a primary male.     

Validation of daily increment formation in otoliths of juvenile and adult European anchovy

The otoliths of juveniles and adults of European anchovy Engraulis encrasicolus held in aquaria were marked by immersion in oxytetracycline hydrochloride (OTC) at concentrations between 350 and 410 mg l⁻¹ for 12 h. Counts of microincrements between fluorescent bands validated the daily otolith increment formation. The otolith increments were easily readable at ×400 with average increment widths of c . 1·1 µm. Validation was successfully demonstrated in juveniles and adults maintained for short periods in the aquaria in the summer. For European anchovy captured as juvenile and reared to adults, however, increment formation appeared less than daily. The daily periodicity of the otoliths in juvenile European anchovy implies that counting of microincrements can be used to study their birth dates. The application of this technique to adults, however, may lead to the underestimation of actual age and further research needs to be done to clarify the reasons for the apparent loss of the daily rhythm over long periods.     

Limits for the detection of daily otolith increments in whitefish (Coregonus lavaretus L.) larvae

The formation of daily otolith increments in European lake white-fish was evaluated in the laboratory during 40 days at 4, 6, and 8 °C under limited and ad libitum food supply. Daily increments were easily identified in larvae reared at 8 °C. At 6 °C and, more, at 4 °C, an unstructured perinuclear zone was formed, and daily increments could only be recognized in the light microscope starting from 10 to 35 days after hatching. In some larvae from the 4 °C groups, no increments at all were found. Scanning electron microscopy (SEM) could not improve increment resolution. Only those increments could be viewed by SEM which were visible in the light microscope as well. We conclude that whitefish larvae which experience low (4–6 °C) temperatures during their first weeks of life, hence those which hatch in the lake, cannot be aged by the currently employed preparation techniques.     

Effects of confinement stress of variable duration on the growth and microincrement deposition in the otoliths of Oreochromis niloticus(Cichlidae)

The effects of chronic confinement stress (1, 5 and 10 days) and of periodic blood sampling on somatic growth and the structure and growth of otoliths was studied in Oreochromis niloticus . During the study, the plasma concentrations of cortisol were measured at various times during the application of stress: they were significantly higher in confined fish than in control fish (mean ±  s . d . 3·40 ± 0·47 v . 1·26 ± 0·62 ng ml⁻¹, P  < 0·05) up to 5 days after the start of a 10 day stress period. The somatic growth (standard length, L _S, and mass) was affected by the confinement and by the sampling (from 16·21 ± 1·07 to 14·64 ± 1·15 cm for L _S, and from 173·31 ± 33·14 to 110·50 ± 29·48 g for mass). But the confinement masked the effect of the sampling on somatic growth. Tetracycline was injected at the start of the experiment to mark the otoliths, and showed that the short and long duration confinements led to a clear check in the pattern of primary increments in the otoliths. The number of primary increments deposited during the resting periods that followed each period of confinement was always less than the number of days that these periods lasted. No relation was found between the duration of confinement and the structure of the resulting checks. These results suggest that there is a disruption in the laying down of primary increments during periods of confinement resulting in an underestimation of their number compared to the actual number of days of growth. These results call into question the use of otolith primary increments as a means of estimating the age of Nile tilapia that have experienced periods of stress.     

Does water calcium content influence the distinctness of daily growth increments in the otoliths of larval whitefish (Coregonus lavaretus L.)?

In larval and juvenile whitefish ( Coregonus lavaretus L.) from Lake Constance, Germany, the otolith increments are deposited daily, whereas daily deposition could not be confirmed in larval whitefish from Lake Pyhäselkä, Finland. The calcium concentration in Lake Constance is high (around 1.3 m m ), while calcium deficiency is typical for Finnish lakes (around 0.15 m m ). Therefore, the hypothesis that the distinctness of daily otolith increments in whitefish is related to water calcium content was tested by rearing three groups of Lake Constance whitefish in water of 0.2, 1.3 and 4.7 m m Ca. The eggs were incubated in lake water (1.3 m m Ca), and the larvae were acclimated to the experimental calcium concentrations on the day of hatching. After 39 days of ad libitum- feeding with Artemia nauplii, the three groups did not differ significantly in total length, wet and dry weight, and otolith length and width. The daily increments were easily recognizable, and contrast between dark (D)- and light (L)-zones was the same in the fish of all test groups. For the experimental set-up of this study, and particularly the range of calcium concentrations tested, the hypothesis that water calcium content influences the distinctness of daily otolith increments was rejected.     

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.     

Otolith microstructure indicating growth and mortality among plaice, Pleuronectes platessa L., post-larval sub-cohorts

Growth and mortality of post-metamorphosed plaice were studied by means of daily increments in the sagittal otoliths. The Gompertz model was the best fit to length-at-age data and there were no significant differences between length-at-age and back-calculated lengths. The microstructure pattern of the otoliths at metamorphosis was also used to estimate hatching and settlement distributions. Differential growth and mortality occurred among sub-cohorts; growth rates and mortality were higher in fish that settled earlier. In 1986, the best survival was for a sub-cohort settling in late May to early June. In contrast, in the warmer season of 1987, survival was highest for the second and third sub-cohorts settling in late April and mid May.