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.     

Nutritional condition and vertical distribution of Baltic cod larvae

Newly hatched Baltic cod Gadus morhua larvae are typically found at depths >60 m. This is a region of low light and prey availability, hence generating the hypothesis that larvae have to migrate from hatching depth to the surface layer to avoid starvation and improve their nutritional condition. To test this hypothesis, Baltic cod larvae were sampled during the spawning seasons of 1994 and 1995 with depth-resolving multiple opening/closing nets. Each larva was aged by otolith readings and its RNA/DNA ratio was determined as a measure of nutritional condition. The RNA/DNA ratios of these larvae aged 2-25 days (median 10 days) ranged from 0.4 to 6.2, corresponding to levels exhibited by starving and fast-growing larvae in laboratory calibration studies (starvation, protein growth rate, G_pi= -12.2% day⁻¹; fastgrowing larvae, G_pi=14.1%day⁻¹) respectively. Seventy per cent of the field caught larvae had RNA/DNA ratios between the mean values found for starving and fed laboratory larvae. Only larvae aged 8-11 days had higher mean RNA/DNA ratios above 45 m than below ( t -test, P<0.05). However, the instantaneous protein growth rates were significantly higher for all larval age groups in the surface layers ( t -test, P<0.05). Starving larvae were found in all depths sampled (10-85 m), whereas growing larvae (positive G_pi) were restricted to samples taken shallower than 45 m. These superior growth rates above 45 m corroborate the hypothesis and imply that migration to the shallow water layers is a prerequisite for good nutritional condition, growth and survival of Baltic cod larvae. The frequent occurrence of cod larvae older than 8 days in the deep water in poor condition suggests that a proportion of the larvae will die from Starvation in the deep layers of the Baltic Sea.     

Larval development,growth and age determination in the sharpnose pufferfishCanthigaster valentini (Teleostei: Tetraodontidae)

The eggs, early larvae and juveniles of the sharpnose pufferfishCanthigaster valentini are described, based on material collected in Great Barrier Reef waters. Eggs were obtained in the field by divers and reared in the laboratory. The eggs are spherical, strongly adhesive, 0.68–0.72 mm in diameter, possess a dense cluster of small oil droplets, and hatch around sunset 3 to 5 days after fertilization. Newly hatched larvae have a small yolk sac, pectoral fin folds, 17 myomeres (6 pre-anal, 11 post-anal) and measure 1.30–1.40 mm in notochord (standard) length. The eggs ofC. valentini differ from those of other tetraodontids in being much smaller and having a longer incubation time. The larvae can be distinguished from other tetraodontid larvae by pigmentation, myomere count and size at hatching. Growth is most rapid during the first day of larval life. Age determinations (based on otolith microstructure) of field collected juveniles, both pelagic and newly settled, indicate a pelagic phase of between 64 and 113 days for this species. This estimate appears consistent with the extended pelagic juvenile stages observed in other tetraodontiform fishes and could indicate thatC. valentini can delay settlement for some time after becoming competent to settle at a minimum age of 64 days.     

Microstructural growth in otoliths of black rockfish,sebastes schlegeli, from prenatal larval to early juvenile stages

Microstructural growth in the sagittae ofSeastes schlegeli, a viviparous scorpaenid, is described from prenatal larval to early juvenile stages, and related to morphological changes. Embryos and prenatal larvae were extruded from a gravid female from 21 d prior to birth onwards, and released larvae reared and sampled up to 58 d after birth. Eggs hatched in the ovary 14 d prior to birth. At this time, otoliths consisted of a core surrounded by a prominent check, similar to the otolith structure seen in oviparous fishes. Fourteen growth increments had been deposited by birth. The parturition mark it-self comprised a prominent check and narrow growth increment Growth increments were deposited daily from hatching up to 58 d after birth, whereas accessory primordia first appeared in otoliths by ca. 32 d after birth, at a specimen total length of ca. 13 mm. This corresponded to the period during which the larvae metamorphosed into juveniles. Otoliths grew exponentially during the larval stage and linearly during the juvenile stage. when plotted against total length. Growth in total length from hatching to 58 d after birth could be represented by the Gompertz curve.     

Early life history of herring larvae in contrasting feeding environments determined by otolith microstructure analysis

Newly hatched autumn-spawned herring larvae Clupea harengus were released in two 2500-m³ outdoor mesocosms and reared over a 2-month period. Hydrographic conditions were similar in the two mesocosms, but the average plankton density was initially more than 10 times higher in mesocosm B compared to mesocosm A (>11⁻¹ v. <0.11⁻¹). Half-way through the experiment the feeding conditions reversed with three times higher average densities in mesocosm A than in mesocosm B (>31⁻¹ v. ∼11⁻¹). Herring larvae were sampled with a 0.3-m² two-chambered net twice weekly, and survivors were harvested by draining the mesocosms at the end of the experiment. Otolith growth trajectories of individual larvae were determined by relating radial otolith size with number of increments from the outer edge of the otolith (days before capture). The increment widths during the first 3 weeks after hatching, including the first-check size, were generally wider among larvae from mesocosm B (relatively good initial feeding conditions) than among those from mesocosm A (poor initial feeding conditions). The otolith growth pattern also confirmed that the surviving herring in mesocosm A belonged to the upper size range of larvae in the mesocosm after only 2–3 weeks from hatching; no such trend was found in mesocosm B. In both mesocosms the otolith size-at-age indicated that with the present sampling gear, herring larvae larger than 20–25 mm were underrepresented in the net samples. The information obtained from otolith-size-at-age is compared with other morphometric and biochemical measures of size and condition of larvae obtained throughout the experiment.     

骨唇黄河鱼耳石早期形态发育和轮纹特征研究

研究了骨唇黄河鱼仔稚鱼耳石在实验室养殖条件下的发育过程和生长特点,确证了轮纹沉积规律。结果表明,在14.0-17.8℃孵化条件下,微耳石和矢耳石在受精后96h 30min出现,星耳石在出膜后第16天出现。仔稚鱼生长过程中矢耳石形状变化较大,由出膜时的圆形发育到稳定时的箭矢状。微耳石由近圆形发育成贻贝形,其中心核位置随发育明显偏移。星耳石形状不规则,从出现时的心形发育成为星芒状。微耳石和矢耳石在前后轴方向上后区的生长快于前区（P0.05）;在背腹轴方向上,微耳石腹区的生长快于背区（P0.05）,矢耳石背区的生长快于腹区（P0.05）,两对耳石的前后区半径之和与全长均呈线性相关。微耳石和矢耳石的第1个轮纹均在出膜后第2天形成,新增的轮纹数（微耳石IL,矢耳石IS）与出膜后的天数（D）表现出显著的线性相关,方程分别为: IL=0.9911D-1.0008（R2=0.9971,n=220,P0.001）和IS=0.9925D-0.10873（R2=0.9919,n=161,P0.001）,方程的斜率与1均无显著差异（P0.05）,表明两对耳石轮纹沉积均呈日周期性,生长轮为日轮。研究结果丰富了骨唇黄河鱼的发育生物学资料,可为研究其自然种群早期生活史提供参考。       

不同温度对三叶虫萤卵孵化和初孵幼虫发育的影响

本文研究了三叶虫萤Emeia pseudosauteri在不同恒温设置和室内变温条件下卵孵化率和初孵幼虫存活率,并通过直接最优法和直线回归法计算出了三叶虫萤卵的发育起点温度和有效积温。结果表明:12~30℃恒温条件下,卵的孵化率随着温度升高显著下降(P<0.05),且均低于室内变温条件(P<0.05)下的孵化率;初孵幼虫在恒温15℃下的存活率最高,为73.13%;低于12℃和高于30℃恒温中初孵幼虫均无法存活;在恒温条件12~30℃下,卵的发育历期随温度升高而缩短,其中恒温12℃下最长,发育历期为42.96 d(n=3),恒温30℃下最短,发育历期仅12.75 d(n=3)。通过直接最优法计算出三叶虫萤卵的发育起点温度为3.52℃,有效积温分别为382.20 d·℃。上述结果为三叶虫萤的人工繁育提供了参考。     

Effects of growth rates on the otolith increments deposition rate in capelin larvae (Mallotus villosus)

Otolith microstructure analysis was applied to known age capelin larvae (Mallotus villosus) in order to examine the formation of daily increments. In two validation experiments, newly hatched yolk sac larvae were stocked into eight 10 m³ plastic bags where environmental conditions were kept as natural as possible. The bags were terminated after 35-79 days, the surviving larvae were collected and the otoliths were analysed. Survival in the bags varied between 39 - 71% with average individual length growth rates of 0.25 mm day^- 1. The ages of most larvae were underestimated and the accuracy in age estimation was generally low. Highest accuracy was found for fast growing larvae. On average, the larvae started to form increments about 12 days after hatching, and the increment width increased with age and/or length of the larvae. Larvae showing low body growth rates had fast otolith growth relative to body length.     

三峡库区木洞江段翘嘴鲌早期生长特征研究

2013 年 910 月在三峡库区木洞江段采集翘嘴鲌(Culter alburnus)幼鱼, 摘取微耳石进行耳石微结构分析, 推算了翘嘴鲌幼鱼的日龄及孵化日期, 探讨其早期生活史阶段的生长特征。结果显示, 采集 97 尾翘嘴鲌幼鱼, 体长范围为 4098 mm。翘嘴鲌幼鱼的微耳石形状为不规则扁椭球形, 耳石横截面磨片上具有一个核和一个原基。耳石原基的直径为11.627.8 m, 平均值为(18.63.8) m。耳石核中心到第一个生长轮的距离为(13.04.7) m。翘嘴鲌幼鱼的日龄为 44104d, 推算其孵化日期为 2013 年 6 月 9 日至 8 月 17 日, 高峰期为2013 年7 月9 日至7 月22 日。耳石半径与体长、日龄与体长之间均呈显著的线性关系(P0.05)。耳石日轮宽度随着日龄的增加不断变化显示, 三峡库区翘嘴鲌早期生活史阶段的生长速率不断变化, 日平均生长率为0.774 mm/d。       

Early ontogeny of Ancherythroculter nigrocauda and effects of delayed first feeding on larvae

Development of embryos and larvae in Ancherythroculter nigrocauda Yih et Woo (1964) and effects of delayed first feeding on larvae were observed after artificial fertilization. The fertilized eggs were incubated at an average temperature of 26.5°C (range: 25.7–27) and the larvae reared at temperatures ranging from 21.8 to 28°C. First cleavage was at 50 min, epiboly began at 7 h 5 min, heartbeat reached 72 per min at 24 h 40 min and hatching occurred at 43 h 15 min after insemination. Mean total length of newly hatched larvae was 4.04 ± 0.03 mm (n = 15). A one‐chambered gas bladder was observed at 70 h 50 min, two chambers occurred at 15 days, and scales appeared approximately 30 days after hatching. Larvae began to feed exogenously at day 4 post‐hatch at an average temperature of 24°C. Food deprivation resulted in a progressive atrophy of skeletal muscle fibres, deterioration of the larval digestive system and cessation of organ differentiation. Larval growth under food deprivation was significantly affected by the time of first exogenous feeding. Starved larvae began to shrink, with negative growth from day 6 post‐hatch. The point of no return (PNR) was reached at day 11 after hatching. Mortality of starved larvae increased sharply from day 12 after hatching.     

Tetracycline tagging in coregonid embryos and larvae

Coregonus peled (Gmelin) embryos at the eyed stage were immersed in tetracycline hydrochloride (TC) solution (600 mg l⁻¹) and fluorescent marks on the otoliths from fish were identified under a UV light microscope. Three weeks after treatment, when the larval fish had hatched, multiple primordia of the sagitta had fluorescent bands whose locations suggest that calcification begins before formation of the otolith's core. Upon hatching, increments were few or absent, and daily increments started forming after hatching. In coregonid larvae immersed in TC solution immediately after hatching, the fluorescent band was only 1 day's growth increment wide in the otolith. The age of larvae based on ring counts after marking corresponded to the actual age, but further studies are required. Triple marks due to 35-h immersions in TC solution separated by 5–7 day feeding periods were clearly readable in the otoliths. One month after treatment the fluorescent marks were identified under UV light on otoliths from every fish. In treated embryos, 38% of fish had marks 3 months after TC immersion, whereas in treated larvae 60–80% of fish grown up to 38.7 mm were marked.     

Rearing of Procypris rabaudi during early life-history stages

The early life‐history of Chinese rock carp Procypris rabaudi was investigated during a 56‐day rearing period: 318 artificially propagated P. rabaudi larvae were reared throughout metamorphosis in a small‐scale recirculation system (345 L water volume, 10 × 18 L rearing tanks, 150 L storage and filter compartment with bioballs, 20–30 larvae L^?1) at the Institute of Hydrobiology, Wuhan, Hubei Province, China. The newly hatched larvae had an initial total length of 8.93 ± 0.35 mm SD (n = 10) at 3 days post‐hatch and reached an average total length of 33.29 mm (±1.88 mm SD, n = 10) 56 days after hatching. Length increment averaged 0.45 mm day^?1, resulting in a mean growth of 24.4 mm within the 56‐day period. High mortality rates of up to 92% derived from an introduced fungus infection and subsequent treatment stress with malachite green. Our results indicate that Chinese rock carp can be raised successfully from artificially fertilized eggs. We therefore assume this species to be a candidate for commercial aquaculture.     

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 shape analysis and daily increment validation during ontogeny of larval and juvenile European chub Squalius cephalus

This assesses features of otoliths from laboratory-reared embryos, larvae and juvenile European chub Squalius cephalus from hatching to 180 days post-hatching (dph). We observed the development of the three pairs of otoliths (lapilli, sagittae and asterisci) and more precisely shape changes, as well as timing and deposition rate of increments of the lapilli. The lapilli and the sagittae were present at hatching, whereas the asterisci formed between 20 and 30 dph. The lapillus and sagitta shapes were round until 20 dph. From 60 dph the anterior and the posterior rostra of the sagittae were well developed, but very thin, making this otolith too fragile to manipulate for further studies of shape and validation of otolith increment deposition rate. The lapilli provided reliable age estimates for free embryos, larvae and juveniles up to 120 dph. However, caution should be taken when ageing fish older than 150 dph as an underestimation was noticeable. The regression of the number of otolith increments on age showed a slope and an intercept not significantly different from 1 and 0, respectively, which indicated that otolith growth increments were deposited on a daily basis, with the first microincrement occurring at hatching. Increment counts were consistent between three interpreters, indicating a consistent and reliable age estimate. This study validates that the otolith increment deposition rate can be used to assess hatching dates and daily growth of wild S. cephalus under 150 dph and in environments similar to the conditions used in this study.     

Maternal transfer of cadmium tolerance in larval Oreochromis mossambicus

Exposing female tilapia to Cd did not affect reproduction and egg quality, nor the survival of their offspring. The LT ₅₀ of Cd-exposed larvae (within 24 h post hatching) from Cd-treated female Oreochromis mossambicus (mean ±S.E.=10·9±0·5 days, n =4) was greater than that of Cd-exposed larvae from control females (6·9± 1·2 days, n =4). A substantial amount of metallothionein mRNA (MT mRNA) was found in both oocytes and newly hatched larvae from Cd-treated females, but MT mRNA levels were low in newly fertilized eggs. The amount of MT mRNA was very low in all these stages in the control group. Cadmium could not be detected at any stage for either control or Cd-treated group, and metallothionein protein levels were also very low in both groups. The early appearance of MT mRNA in oocytes and newly hatched larvae from Cd-treated females may result in early translation after hatching and explain their tolerance to Cd.     

An alternative method for the preservation of tropical fish larvae

Preservation of newly hatched fish larvae in a 30% ethanol freshwater solution kept at −19° C allowed accurate measurement of morphology and otolith dimensions with minimal error due to shrinkage compared to other concentrations of ethanol or gluteraldehyde.     

Observation of the embryonic development in Pseudoplatystoma coruscans (Siluriformes: Pimelodidae) under light and scanning electron microscopy

Pseudoplatystoma coruscans is a very popular species for tropical fish culture as it has boneless meat of delicate taste and firm texture. Few studies on fish reproductive biology refer to the morphological features of eggs. The goal, therefore, of this present work was to perform a structural and ultrastructural analysis of fertilization and embryonic development in P. coruscans. The incubation period, from fertilization to hatching, lasts 13 h at 28/29 degrees C and 18 h at 27 degrees C. The oocytes had a mean diameter of 0.95 mm and hatched larvae were 2.55 mm in diameter. Analysing their development, we observed round, yellow oocytes that bore a double chorion membrane and a single micropyle. At 10 s after fertilization, several spermatozoa were detected attached to the oocyte surface. After 1 min of development, a fertilization cone that obstructed the micropyle could be observed. Segmentation started between 20 and 30 min after fertilization, when the egg cell was then formed. The first cleavage occurred between 30 and 45 min after fertilization, prior to reaching the morula stage (75 and 90 min after fertilization). The epiboly movement started at 120 and 180 min after fertilization and ended at 360 and 480 min after fertilization. Differentiation between cephalic and caudal region was detected after 420 and 600 min after fertilization and larvae hatched between 780 and 1080 min after fertilization. Seven main embryonic development stages were identified: egg cell, cleavage, morula, blastula, gastrula, segmentation with differentiation between cephalic and caudal regions, and hatching.     

Seasonal changes in the physiology of brook trout, Salvelinus fontinalis (Mitchill), in a sub-Arctic river system

Wild herring larvae were sampled from the Firth of Clyde, Scotland in 1980 and 1981 to assess the suitability of otolith ageing methods for herring larval studies. The ages and growth rates were estimated directly from otolith ring counts, by comparison of ring counts with the results of validation studies on reared larvae of known age, and by back-calculation. Growth rates based on otolith data were compared with indirect calculations based on length at capture. The assumption of daily ring deposition, even allowing for a period of lag before the initiation of daily ring deposition, led to incorrect predictions for age at yolk-sac absorption, and back-calculations led to overestimated growth rates, indicating that ring deposition does not begin at hatching and that light microscope counts give a rate different from one ring per day in wild herring larvae.     

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

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

Age and 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.