Somatic growth and otolith microstructure of larval and juvenile pacific cod <Emphasis Type="Italic">Gadus macrocephalus</Emphasis>

ABSTRACT:   Microstructures of sagittae and lapilli were examined in relation to somatic growth for reared larvae and juveniles of Pacific cod. The Laird–Gompertz model was fitted to the daily age and somatic growth relationship. Growth increments were deposited on a daily basis in both kinds of otoliths, with a check formed at hatching. Two subsequent checks and an accessory primordia (AP) occurred in the sagittae. The lapillus was adequate for increment width measurement through the early life stages. Sagittal and frontal plane of sagitta was adequate for measurement in the pre-AP and post-AP formation stages, respectively. The shift of desirable plane was caused by changes in otolith and increment shapes with AP formation. Back-calculated total lengths using the biological intercept method did not significantly differ with certain body lengths ( P  > 0.05), suggesting validity of back-calculation in this species. Using the back-calculated total length, morphological and ecologic changes that seemed to affect checks and AP formations are discussed.     

Otolith microstructure of brown sole <Emphasis Type="Italic">Pseudopleuronectes herzensteini</Emphasis>: validation of daily ring formation and the occurrence of microstructure denoting metamorphosis

Brown sole Pseudopleuronectes herzensteini larvae and juveniles were reared to validate daily otolith ring formation. At 15°C, a check (a distinct ring) formed on the sagittae and lapilli at 6 days after hatching, and clear increments regularly formed outside the check. For both otoliths, the relationship between the number of days after hatching and number of increments was linear, and the slope of the line was approximately 1; therefore, daily formation was validated. At 12°C, the check formed on the lapillus 8 days after hatching. Accessory primordia (AP) began forming on the sagittae of metamorphosing larvae, and the shape of the sagittae became complicated. AP were not formed on the lapillus; concentric rings were formed throughout larval and juvenile stages. Wide and obscure increments formed on the lapilli during metamorphosis (metamorphosing zone, MZ). Based on MZ, concentric rings that have formed on the lapilli of juveniles can be separated into larval and juvenile rings. The morphs of large juveniles’ lapilli were bilaterally asymmetric, and the blind-side lapilli were most suitable for otolith microstructure analysis. This study provides fundamental information for otolith microstructure analysis in wild brown sole.     

东海条石鲷仔鱼耳石日轮与生长的关系

2009年4月15日-5月5日在浙江省舟山水产研究所条石鲷(Oplegnathus fasciatus)人工繁殖期间,逐日选择胚胎和仔鱼样本,连续解剖观察发育后期胚胎和前期仔鱼,光镜观察仔鱼矢耳石和微耳石的形态、日轮数,测定其直径,研究条石鲷的耳石日轮和生长。结果表明,受精后约26h,条石鲷胚胎听囊内出现1对矢耳石和1对微耳石;仔鱼孵出第2天形成第1个轮纹,之后每天形成1轮,孵化后天数(N)和矢耳石日轮数(D)的关系为N=D+1;在第8天左右,矢耳石上出现第2条明显的标记轮,为初次摄食轮。仔鱼耳石长径(rs,μm)与鱼体体长(L,mm)呈线性相关,其关系式为rs=18.146L-44.436;矢耳石长径rs与微耳石长径rl之间存在线性相关,其关系式为rs=0.6125rl+1.9882。根据结果确认,矢耳石轮纹可作为条石鲷仔鱼日龄的判别依据。     

An individual-based model for the direct conversion of otolith into somatic growth rates

Otolith increment width and larval fish data (length and weight) were used to develop an individual‐based model (IBM) to describe daily resolved growth rates of North Sea herring (Clupea harengus) larvae (Autumn Spawners) caught during International Herring Larvae Surveys in the ICES area IVa from 1990 to 1998. The model combines sagittal otolith readings (core and individual increment measurements), larval standard length and weight data, and solves an over‐determined set of linear system equations for all parameters using the method of least square residuals. The model consists of a matrix, which describes the increment width formation of 119 larvae, a vector containing their length/weight measurements, and a vector describing residuals. The solution vector yields age‐dependent maximum somatic growth rates of herring larvae up to an age of 41 days with sizes ranging from 10 to 25 mm. The observed environmental temperature in which larvae dwelled was relatively uniform. Therefore, measured increment width was individually used to determine daily growth from any single larva in relation to their potential maximum growth under optimal feeding conditions. The results are discussed with respect to the spatial and temporal variability of larval occurrence. Finally, an analysis of error estimation of the larval growth characteristics is presented.     

Interannual variability in hatching period and early growth of juvenile walleye pollock, Theragra chalcogramma, in the Pacific coastal area of Hokkaido

Juvenile walleye pollock of the Japanese Pacific population were collected from the Funka Bay [spawning ground; 16–64 mm fork length (FL)] in spring and the Doto area (nursery ground; 70–146 mm FL) in summer. Hatch dates were estimated by subtracting the number of otolith daily increments from sampling dates, and their early growth was back‐calculated using otolith radius–somatic length relationships. Interannual change of the hatching period was observed during 2000–02, and the peaks ranged from mid‐February in 2000 to early‐April in 2002. In 2000, when a strong year class occurred, early life history of the surviving juveniles could be characterized by early hatching and slower growth in the larval stage (<22 mm length). Higher growth rate in 2001 and 2002 did not always lead to good survival and recruitment success. Even though their growth was slow in 2000, the larvae hatched early in the season had larger body size on a given date than faster‐growing larvae hatched in later season in 2001 and 2002. Bigger individuals at a certain moment may have advantage for survival. The delay of hatching period may result in higher size‐selective mortality, and as a necessary consequence, back‐calculated growth in 2001 and 2002 could shift towards higher growth rate, although abundance of such a year class would be at the lower level. Variability in spawning period, early growth and their interaction might have a strong relation to larval survival through cumulative predation pressure or ontogenetic changes in food availability.     

Validation of daily increment formation in otoliths of immature and adult Japanese anchovy <Emphasis Type="Italic">Engraulis japonicus</Emphasis>

In order to validate daily increment formation in otoliths of immature and adult Japanese anchovy Engraulis japonicus, three rearing experiments using chemical marking of otoliths were conducted on adult anchovy in summer 2004 and immature anchovy in summer 2005 and in winter 2006. In the two experiments conducted in summer, the number of otolith microincrements between alizarin complexone (ALC) marks showed that microincrements were formed daily. In the summer 2005 experiment, immature anchovy under conditions of reduced daily food rations also showed daily microincrement formation. Average increment width was 0.9 μm in adults and 1.8–3.1 μm in immature anchovy. In contrast, no clear increments were observed between ALC marks on the otoliths from the experiment in winter 2006, and scanning electron microscope (SEM) observations failed to confirm clear increment formation. We consider that low water temperatures (<13–14°C) restricted otolith growth and lowered the contrast between the discontinuous and the incremental zones of the otolith increments. For age estimation of Japanese anchovy, clear increments wider than about 1 μm in the otolith can be regarded as daily increments. However, daily age estimation of immature and adult anchovy that experience low water temperatures in winter may be difficult due to the obscurity of the increments.     

Occurrence and distribution during the post-settlement stage of two Choerodon species in shallow waters around Ishigaki Island, southern Japan

The recruitment patterns of black-spot tuskfish Choerodon schoenleinii were compared with those of orange-dotted tuskfish (OT) C. ancholago. Individuals at the settlement and juvenile stages were collected using a push net in the intertidal zone and a seine net in seagrass beds. Relative values of standard length to total length (TL) for the two Choerodon species indicated an inflection point at approximately 10?C20?mm TL, suggesting that both species complete metamorphosis at a similar size. However, their temporal and spatial occurrence patterns were distinct. Newly settled individuals (postflexion stage) of black-spot tuskfish were collected mainly within foliage of Sargassum plants of the intertidal zone around March?CApril, while those of OT occurred in both the intertidal zone and seagrass beds mainly in May and June. In seagrass beds, the abundances of both species increased from May or June; however, the TL of black-spot tuskfish was bigger than that of OT. Therefore, black-spot tuskfish progressively migrate to seagrass beds after settling and completing metamorphosis in the intertidal zone, indicating that they utilize two different habitats as nursery grounds. Early spawning and migration from the intertidal zone by this species contributed to the occurrence of relatively large individuals in seagrass beds.     

Transpositional feeding rhythm of loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis> from larvae to juveniles and its ontogenesis under artificial rearing conditions

The diel feeding rhythm and ontogenesis during early life stage of loach Misgurnus anguillicaudatus were investigated under experimental conditions (light: L 06:00–18:00, D 18:00–06:00 h). Morphological and behavioral developments of loach from newly hatched to 40 days after hatching were observed. Larvae were able to prey on daphnia 3–4 days after hatching at 23 ± 0.5°C. As the larvae grew, they showed an increasing feeding capacity and a distinct feeding rhythm. Feeding intensity and incidence for day-4 larvae were highest at 10:00 and 16:00 h. The highest levels of feeding intensity for day-12 larvae occurred at 08:00, 12:00, and 18:00 h as did feeding incidence. By day 20, when the larvae metamorphosed, the highest levels of feeding intensity occurred at 06:00, 18:00, and 24:00 h and were concurrent with the highest feeding incidence. After metamorphosis, feeding capacity had again increased considerably and, in contrast to the earlier stages before day 20, feeding intensity for day-30 juveniles peaked at 05:00 and 20:00 h, about 1–2 h after the maximum feeding incidence. The feeding rhythm of loach juveniles at day 40 was almost the same as the day-30 juveniles. The estimated maximum daily feeding rates were 43.1%, 33.4%, 19.0%, 12.8%, and 5.8% of body weight on days 4, 12, 20, 30, and 40, respectively. Thus, loach was found to have different feeding rhythms in the pre- and post-metamorphosis stages, with the highest feeding activity in daytime during the larval planktonic stage before metamorphosis, and intensely nocturnal feeding behavior during the juvenile benthic stage after metamorphosis.     

Effects of different step‐wise temperature increment regimes during egg incubation of Atlantic cod (Gadus morhua L.) on egg viability and newly hatched larval quality

We carried out an experiment to determine how rapidly the early incubation temperature of Atlantic cod eggs can be increased without affecting normal embryonic development and hatching. Atlantic cod eggs were incubated at a constant low temperature (4.5 ± 0.5°C; T5 – control) and four temperature increment treatments where the temperatures were increased stepwise from 4.5°C at zygote stage to 9.5 ± 05°C (T1‐8 h, T2‐32 h, T3‐64 h and T4‐96 h). Embryonic cell symmetry, embryonic mortality, hatching success and larval skeletal abnormalities, length and yolk sac volume were recorded. Larval samples were also taken at hatch for histological analysis. Except for higher egg mortality and lower hatching success in the T1, the differences among experimental groups were minor. Cell asymmetries and embryo mortalities were not significantly different between the control and T2–T4 treatment groups. Control larvae were significantly longer and had smaller yolk reserves at hatch than T1–T4 larvae and larvae from T2 had the largest yolk reserves. Tissue and organ histology of hatched larvae were similar. Considering embryonic cleavage pattern, hatching success and larval morphology and histology, a gradual increment of temperature in 32 h seems to be the better choice for future developmental programming studies in Atlantic cod.     

Faster growth before metamorphosis leads to a higher risk of pseudoalbinism in juveniles of the starry flounder <Emphasis Type="Italic">Platichthys stellatus</Emphasis>, as suggested by otolith back-calculation

The mechanism underlying malformation during flatfish metamorphosis is not clear. Here, the relationship between growth before metamorphosis and the occurrence of malformation after metamorphosis was examined in individuals reared in a single tank. Otoliths of starry flounder Platichthys stellatus larvae were labeled with alizarin complexone before metamorphosis [12 days after hatching (DAH)]. The positive linear regression between the lapillus otolith diameter and body length at 12 DAH enabled the estimation of individual larval size after completion of metamorphosis. At 12 DAH, the average body length of the typical pseudoalbino juveniles was significantly greater (5.37 mm) than that of the normal juveniles (5.13 mm) (P < 0.01, n = 100). In addition, of the larvae that were estimated to measure less than 4.8 mm at 12 DAH, approximately 80% metamorphosed into normal juveniles, whereas more than 60% of the larvae that measured more than 5.4 mm became pseudoalbino juveniles. These results indicate that the larvae that grow rapidly during the first 12 days are more likely to become pseudoalbino individuals after metamorphosis.     

Effects of the timing of initial feeding on growth and survival of loach (<Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>) larvae

The effects of delayed first feeding on growth and survival and starvation on the point-of-no-return of loach Misgurnus anguillicaudatus larvae were studied by evaluating morphometric characteristics under controlled conditions. Larvae began to feed exogenously at 3 days after hatching (DAH) and the PNR occurred between 9 and 10 DAH at 23 ± 1.0°C. The experimental design included a conventional feeding regime with initial feeding from 3 DAH as a control, delayed first feeding for 4, 5 and 6 DAH. Morphometric characteristics (head depth, body depth, eye diameter, mouth diameter, musculature height, total length and yolk sac volume) were evaluated under different initial feeding time (3, 4, 5 and 6 days after hatching). Loach larvae initiated first feeding at 4, 5 and 6 days after hatching achieved comparatively lesser growth performance in all morphometric characteristics than that of 3 days at the end of the experiment. By day 6, significant differences were observed between 3 and 6 days initial feeding larvae for all morphometric characteristics except eye diameter and mouth diameter. Similarly, significant differences were noticed between 3 and 5 days initial feeding. However, there were no significant differences in head depth, body depth, eye diameter, mouth diameter, and total length between 3 and 4 days initial feeding until 12 DAH. After 15 days rearing, significant differences in all morphometric characteristics appeared between 3 and 4 days initial feeding and followed to the end of the experiment. It was also observed that the yolk absorption in loach larvae was completed by 6 days irrespective of the differences in the initial feeding. The yolk volume of 4 and 5 DAH larvae initiated first feeding at 3 days (0.0125 ± 0.0015; 0.0077 ± 0.0009 mm³) had significant differences compared with yolk volume of larvae initiated first feeding at 4 days (0.0081 ± 0.0011; 0.0039 ± 0.0004 mm³), 5 days (0.0079 ± 0.0010; 0.0017 ± 0.0002 mm³) and 6 days (0.0082 ± 0.0011; 0.0016 ± 0.0001 mm³). Survival rates of four treatments were estimated daily for 30 days and significant differences were observed between the treatments at the end of the experiment. The final survival rate was higher when the loach larvae initiated feeding at 3 days (75.9%) when compared with 4 days (31.8%), 5 days (14.5%) and 6 days (6.4%). The present study suggests that the first feeding of loach larvae should be initiated at 3 DAH for achieving better growth and survival or else bad growth performance will engender if the first feeding is delayed.     

Organogenesis of exocrine pancreas in sharpsnout sea bream (<Emphasis Type="Italic">Diplodus puntazzo</Emphasis>) larvae: characterization of trypsin expression

The ontogeny and differentiation stages of digestive systems related with trypsin expression in larvae of sharpsnout sea bream, Diplodus puntazzo, were investigated from hatching to 40 DAH (days after hatching), and total lengths and weights of larvae were determined. Histologic and enzymatic techniques were used to explain the functional development of the pancreas including trypsin activity. The pancreas was identified as a compact structure located in the region slightly posterior to the liver. At 3 DAH, first anus and then mouth opened. Incipient pancreas secretion polyhedral cells could be first observed as zymogen granules. During larval metamorphosis, the pancreas became diffuse, spreading throughout the mesentery in proximity to the stomach, the anterior intestine and the pyloric caeca. The specific activity of trypsin (42.54 ± 6.8 mU/mg protein⁻¹) was found as early as after hatching at larvae size of 2.87 ± 0.34 mm at 0 DAH. Activity further increased until 10 DAH, especially after exogenous feeding. The highest trypsin activity was detected at 25 DAH as 119.26 ± 11.6 mU/mg protein⁻¹. It is concluded that exocrine pancreas organogenesis is the main critical step in the development of digestive system that results in zymogen granules accumulation and increased trypsin activity.     

Effect of shelter acclimation on the post-release survival of hatchery-reared black-spot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis>: laboratory experiments using the reef-resident predator white-streaked grouper <Emphasis Type="Italic">Epinephelus ongus</Emphasis>

A critical component of many releasing projects is the identification and subsequent implementation of optimal release strategies that can decrease post-release predation mortalities. We performed laboratory experiments to investigate whether acclimation to shelters affects the post-release survival of hatchery-reared black-spot tuskfish Choerodon schoenleinii in the presence of a reef-resident predator, the white-streaked grouper Epinephelus ongus. Tuskfish were exposed to groupers under three different experimental conditions/treatments: (1) acclimation of fish to shelters prior to their exposure to groupers; (2) no acclimation of fish to shelters, but with shelters available during their exposure to groupers; (3) fish not acclimated to shelters and no shelters available during their exposure to groupers. Tuskfish that were acclimated to shelters utilized shelters more frequently than did non-acclimated fish, and the survival rate of acclimated fish was higher than those of fish in the other treatments. These results suggest that pre-release acclimation to shelters improves the post-release survival of hatchery-reared black-spot tuskfish.     

Early life history of the black anglerfish Lophius budegassa Spinola, 1807 in the Mediterranean Sea using otolith microstructure

The early life history of the black anglerfish, Lophius budegassa was investigated by otolith (lapilli) increment analysis. Samples of demersal juvenile L. budegassa ranging from 54 to 196 mm total length were collected during bottom trawl surveys in the central Adriatic Sea. By counting increments presumed to be deposited daily in the lapillar otoliths, 88 specimens of L. budegassa were successfully aged. Age estimates of juveniles ranged between 79 and 204 days, indicating that probably the pelagic phase of this species is relatively short and settlement occurs at less than 3 months of life. The analysis of check marks in the core area of lapilli enabled us to determine the period of endogenous feeding, which would last between 15 and 24 days after hatching. Back-calculated hatching dates and, consequently, the spawning season of L. budegassa in the Adriatic Sea was spread over a long period, lasting at least from February to June. The length at age relationship gave an estimate of mean growth rate of approximately 0.8–1.02 mm/day, indicating a faster growth rate of 0+ juveniles L. budegassa than previously thought. The implications of these findings on age estimates discrepancies between previous ageing studies on L. budegassa carried out using different calcified structure (sagittae or illicia) are discussed.     

Seasonal changes in otolith and somatic growth in age-0 Pacific saury <Emphasis Type="Italic">Cololabis saira</Emphasis>

We evaluated the seasonal changes in otolith and somatic growth of age-0 Pacific saury Cololabis saira in 223 fish collected between June and November 2002. We calculated the age in days of each individual by measuring otolith growth increments under a scanning electron microscope. The age was correlated with body length and otolith radius. We also observed seasonal changes in the rate of increase in body length and otolith radius and in the pattern of otolith growth. Until August, both body length and otolith radius increased with age. Thereafter, the otolith radius continued to increase, whereas the rate of somatic growth decreased. As a result, the ratio of otolith radius to body length increased. After August, the percentage of otoliths with unreadable increments on their edge increased due to the formation of hyaline zones. Otoliths grew both radially and in thickness until July, but gradually stopped growing in thickness after August. Beginning in October, more than 80% of otoliths only grew radially. After August, the otolith not only continued growing but the morphological growth pattern also changed.     

Seasonal changes in otolith increment width trajectories and the effect of temperature on the daily growth rate of young sardines

We studied the otolith microstructure and growth of sardine, Sardina pilchardus, in the North Aegean Sea (eastern Mediterranean Sea), using samples of larvae and juveniles that had hatched in winter (November–January) and winter–spring (February–May), respectively. The juveniles had developed during an extended period coinciding with marked pelagic ecosystem changes (from winter, mixed conditions to summer, stratified waters). To examine the relationship between environmental changes and the observed variability in their otolith increment–width trajectories (width‐at‐age), we summarized the shape of trajectories with a four‐parameter set estimated from a growth model fit to each width trajectory. The individual parameter sets were then related to the potential oceanographic conditions that fish experienced during their development, derived from a hydrodynamic–biogeochemical model (POM‐ERSEM), implemented in the sampling area. Substantial seasonal effects were demonstrated on the otolith microstructure (platykurtic versus leptokurtic trajectories in winter‐mixed versus summer‐stratified conditions), which were related to the progressive sea surface warming. In a subsequent step, in order to study the effect of oceanographic conditions on larval and juvenile daily growth rates, a GAM (Generalized Additive Model) analysis of otolith increment widths was carried out, using model‐derived oceanographic parameters and taking into account the ‘inherent otolith growth’, expressed by the explanatory variables ‘previous increment width’ and ‘Age’. Results showed a strong and positive, linear effect of temperature on the growth rate of winter‐caught larvae, whereas in juveniles, which had developed within a wide range of temperatures, an optimum temperature for growth was observed at around 24°C.     

依耳石显微结构判断安氏新银鱼的早期生活史

安氏新银鱼的矢耳石呈不规则卵圆形。60尾样品(体长37~52 mm)耳石长半径y与体长x呈线形关系,y=260.335+2.6234x。光镜下观察了耳石制片的显微结构。耳石中心圆形的核平均直径(25.17±2.40)μm(SD,后同)。核中心原基平均直径(7.80±2.22)μm。核周围为同心环纹,即日轮。耳石上日轮数73~101,78.3%的样品分布于83~97日轮范围内。前10个日轮平均间距最窄,为1.76μm,之后日轮间距逐渐增宽,60~70日轮平均间距最宽(2.70μm),而后日轮间距又变窄。依日轮间距推算的体长生长,前10日龄平均日增长0.34 mm,以后生长加快,60~70日龄平均日增长最快,为0.52 mm。依据采样日期,日轮数和胚胎发育期推断,样品鱼的产卵期为4月中旬至5月中旬,出生日期为4月下旬至5月下旬。从最初2~3个日轮间距最宽,4~10日轮间距较窄判断,其卵黄营养期为3~4 d,混合营养期为6~7 d。部分样品在48~72日轮处有过渡轮,应是由近海(盐度27~30)到河口(盐度6~18)盐度急剧变化诱导形成的,表明幼鱼有到河口摄食洄游的习性。     

Otolith size differences during early life of dwarf and cannibal Arctic char (Salvelinus alpinus)

In Arctic and alpine lakes, Arctic char [Salvelinus alpinus (L.)] often form two distinct morphs: invertebrate feeders (‘dwarfs’) and piscivores (‘giant or cannibals’). Here, we test for early life history growth variation in dimorphic Arctic char as a proximate explanation for the observed life history variation between the two forms. Char were sampled in 11 alpine and Arctic Norwegian lakes. Dwarfs (defined as sexually mature char less than 15 cm long; N = 304) had a mean total length of 105 mm, whereas the typical cannibal (body length above 20 cm; N = 153) was 388 mm long. A positive correlation between egg size and otolith hatching ring were ascertained in a separate hatching experiment with brown trout (Salmo trutta) and it is assumed that this relationship also is valid for Arctic char, and otolith size was used as a proxy for length. Otolith hatching ring from Arctic char cannibals was larger (mean ± SD; 187 ± 24 μm) than those from dwarfs (mean ± SD; 164 ± 23 μm). There were only minor size differences between dwarfs and cannibals during the next three years, after which dwarfs usually matured. Two mutually nonexclusive, proximate explanations for the differentiation into separate morphs (dwarfs and cannibals) are therefore maternal effects and/or genetic based differentiation. The high catchability of large piscivorous char and low production in alpine and Arctic lake ecosystems may make these stocks particularly vulnerable to overexploitation.     

Structural development of Pacific red snapper Lutjanus peru from hatching to the onset of first feeding

Successful rearing of larval fish requires culture conditions and feeding strategies matching the ontogenetic status of larvae. This study describes the external morphology and development of organs and structures involved in the feeding process (i.e. sensorial organs, mouthparts and digestive system) from hatching until first feeding in Pacific red snapper. Hatching occurred 26 h after fertilization at 26°C and total length (TL) was 2.45 ± 0.08 mm. The larvae showed an undifferentiated eye and digestive tract. At 48 hah, TL was 3.31 ± 0.12 mm. Yolk and oil globule were still present. The mouth was still closed, but the Meckel's, quadrate, hyoid and hyomandibular cartilages were present. The retina was formed by 5 layers, and a thin layer of pigment epithelium was observed in the outer nuclear layer (ONL). At 70 hah, TL was 3.44 ± 0.22 mm. A remnant of oil globule was still present. The mouth and anus were open. At 93 hah, the number of cones in the ONL of the retina have increased and there was more pigment in the pigment epithelial layer. A joint between Meckel's and the quadrate cartilage and also a joint between the hyomandibular cartilage and the skull were present. The presence of live feed was detected in the digestive tract of these larvae. Based on these observations, the Pacific red snapper larvae is functional to start ingesting live feed between the 3rd and 4th day after hatching.     

大黄鱼仔稚鱼不同发育阶段矢耳石形态发育和微结构特征

对人工培育大黄鱼(Larimichthys crocea)的生长发育与矢耳石形态及微结构特征进行研究,结果表明:(1)大黄鱼矢耳石上的轮纹是每日形成的,第1日轮在孵化后第2天形成,与其初次摄食相对应。(2)大黄鱼卵黄囊期和前弯曲期仔鱼的耳石形态为圆形,进入弯曲期耳石长轴迅速伸长,在后弯曲期耳石形态变为椭圆形。进入稚鱼期,矢耳石开始形成次生核。随后次生核数量逐渐增加,在孵化后47～78 d的个体中,次生核数量稳定在5～7个,耳石近似盾形。(3)根据耳石日轮宽度推算的大黄鱼稚鱼在其仔鱼期生长率(b)与第1个次生核的形成时间(tsp1)之间存在明显的线性关系,表明生长较快的个体形成次生核的时间较早,进入稚鱼期所需的时间更短。以上结论表明,大黄鱼矢耳石可以反演其早期生活史阶段的生长发育特征。