Effects of starvation on the formation of daily growth increments in the otoliths of milkfish, Chanos chanos (Forsskål), larvae

The effects of starvation on daily growth and increment formation in the otolith were examined using a double oxytetracycline-labelling method on larval milkfish, Chanos chanos (Forsskål), reared under different feeding regimes. The results indicated that the differences in body and otolith growth between the larvae fed once and three times a day were not significant, and that the otolith growth increment was deposited daily in both groups of fed larvae. In contrast, the starved larvae grew at a slower rate than fed larvae in body length and otolith dimensions, and the otolith growth increment in the starved larvae was not deposited on a daily basis. After undergoing starvation, the larvae were unable to recover their normal growth either in otolith increment deposition or in body and otolith growth even though they were fed. Therefore, the application of ageing techniques based on counting otolith growth increments seems to be inaccurate for starved larvae.     

Daily growth increments in otoliths of milkfish, Chanos chanos (Forsskål), larvae

The formation of daily growth increments of otoliths was studied in the reared larvae of milkfish. The first growth increment was formed during the yolk–sac reabsorption period c .2 days after hatching, and increment formation continued on a daily schedule regardless of growth rate. The initial incremental zone was of amorphous structure, and the subsequent incremental zone was of needle–shaped crystalline structure; the former structure was formed in the yolk–sac reabsorption period of the larva and the latter in the exogenous feeding period. Accordingly, ageing of milkfish larvae is possible by counting growth increments, and timings within the developmental stage of the larvae can be understood by examining the otolith microstructure.     

Linking larval history to juvenile demography in the bicolor damselfish Stegastes partitus (Perciformes: Pomacentridae)

Otolith-based reconstructions of daily larval growth increments were used to examine the effect of variation in larval growth on size and age at settlement and post-settlement growth, survival and habitat preferences of juvenile bicolor damselfish (Stegastes partitus Poey). During August 1992 and 1994, newly settled S. partitus were collected from Montastraea coral heads and Porites rubble piles in Tague Bay, St. Croix, U.S. Virgin Islands (17 degrees 45'N, 64 degres 42' W). Daily lapillar otolith increments from each fish were counted and measured with Optimas image analysis software. S. partitus pelagic larval duration was 23.7 d in 1992 (n = 70) and 24.6 d in 1994 (n = 38) and larval age at settlement averaged 13.0 mm total length both years. Analysis of daily otolith increments demonstrated that variation in larval growth rates and size and age at settlement had no detectable effect on post-settlement survivorship but that larger larvae showed a preference for Montastraea coral at settlement. Late larval and early juvenile growth rates showed a significant positive relationship indicating that growth patterns established during the planktonic stage can span metamorphosis and continue into the benthic juvenile phase. Larval growth rates during the first two weeks post-hatching also had a strong effect on age to developmental competence (ability to undergo metamorphosis) in both 1992 and 1994 with the fastest growing larvae being 8 d younger and 0.8 mm smaller at settlement than the slowest growing larvae. These differential growth rates in early stage larvae established trajectories toward larval developmental competence and may prove important in biogeographical studies of larval dispersal.     

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.     

Effects of temperature,starvation and photoperiod on otolith increments in larval Chinese sucker, <Emphasis Type="Italic">Myxocyprinus asiaticus</Emphasis>

Effects of water temperature, starvation and photoperiod on otolith increment formation in larval Chinese sucker, Myxocyprinus asiaticus, were examined in this study. The results demonstrated that otolith increments of larvae reared under diel temperature fluctuations were very clear and appeared with a high contrast, while those of larvae raised under constant water temperatures were vague or hard to identify. The increment deposition rates were less than 1.0/day in later stage of starvation period. Also, increment deposition was affected by cyclic regimes of water temperature fluctuations, the number of increments corresponded to the cycle times rather than the exact days larvae experienced. However, varying of feeding frequency and photoperiod did not result in any alterations of daily increment formation. Increment width increased obviously with higher rearing temperatures till several days after yolk absorption. However, the width presented an ontogenetic decline during period of endogenous nutrition and the first several days of exogenous nutrition stage. Starvation decoupled the relationship between somatic growth and otolith growth; otolith kept growing, and increment width of starved larvae was similar to those in fed individuals before 9–20 days old; the divergence of increment width from the fed larvae occurred in later stage of starvation period. It can be concluded that temperature regimes and food levels are the major factors affecting increment formation in terms of clarity, deposition rate and width, while photoperiod and feeding frequency have less influence on it.     

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.     

Variability in size-selective mortality obscures the importance of larval traits to recruitment success in a temperate marine fish

In fishes, the growth-mortality hypothesis has received broad acceptance as a driver of recruitment variability. Recruitment is likely to be lower in years when the risk of starvation and predation in the larval stage is greater, leading to higher mortality. Juvenile snapper, Pagrus auratus (Sparidae), experience high recruitment variation in Port Phillip Bay, Australia. Using a 5-year (2005, 2007, 2008, 2010, 2011) data set of larval and juvenile snapper abundances and their daily growth histories, based on otolith microstructure, we found selective mortality acted on larval size at 5 days post-hatch in 4 low and average recruitment years. The highest recruitment year (2005) was characterised by no size-selective mortality. Larval growth of the initial larval population was related to recruitment, but larval growth of the juveniles was not. Selective mortality may have obscured the relationship between larval traits of the juveniles and recruitment as fast-growing and large larvae preferentially survived in lower recruitment years and fast growth was ubiquitous in high recruitment years. An index of daily mortality within and among 3 years (2007, 2008, 2010), where zooplankton were concurrently sampled with ichthyoplankton, was related to per capita availability of preferred larval prey, providing support for the match–mismatch hypothesis. In 2010, periods of low daily mortality resulted in no selective mortality. Thus both intra- and inter-annual variability in the magnitude and occurrence of selective mortality in species with complex life cycles can obscure relationships between larval traits and population replenishment, leading to underestimation of their importance in recruitment studies.     

Recruitment in Japanese sea bass,Lateolabrax japonicas (Cuvier, 1828): effects of timing on spawning and larval quality and quantity

This study aimed to elucidate the causes of variability in larval survival and juvenile abundance (recruitment) within and among cohorts of Japanese sea bass (JSB; Lateolabrax japonicus), a winter‐spawning temperate coastal marine fish. Larvae and settled individuals (settlers) belonging to four cohorts were collected from Tango Bay (the Sea of Japan coast) during eight sampling cruises in 2007 and 2008. Larvae were sampled in January and February each year using an ichthyoplankton net, and settlers were collected in February and March each year using a beam trawl. Age of individual larva and settlers was determined and growth history was back‐calculated from otolith microstructure, and the hatch date distribution was computed. Temperature, daily growth rate, size‐at‐age, hatch date, and density data of larvae and settlers allowed elucidating the effects of the timing of spawning and larval quantity and quality (growth rate and body size) on larval survival and recruitment within and among cohorts of JSB. Results showed that cohorts that hatched earlier in the season had higher quantity of larvae, experienced higher mean temperatures and survived better than cohorts hatched later. Recruitment variability among cohorts is determined largely by the initial quantity of larvae, as this explained >97% of the variability in recruitment among cohorts. Within cohorts, larger hatched larvae grew faster than their smaller conspecifics, and the bigger and faster growing larvae survived and settled. Results from this study suggest the following scenarios for recruitment of JSB: (i) earlier spawning in the season promotes larval survival since earlier cohorts are likely to encounter a better temperature and perhaps food conditions, and therefore recruit better than later cohorts; (ii) the initial quantity of larvae appears to be an important determinant of recruitment variability among cohorts; and (iii) the size‐ and growth‐related mechanisms operating during the larval phase appear to start at the time of the hatch.     

Growth of North Alboran Sea sardine larvae estimated by otolith microstructure, nucleic acids and protein content

Wet mass and DNA, RNA and protein content increased significantly with standard length ( L _S) of sardine Sardina pilchardus larvae, collected in January 1995, in the Bay of Málaga, North Alboran Sea. L _S, wet mass and DNA, RNA and protein content were closely related allometrically to otolith radius ( R ). Larval daily length increments decreased but DNA, protein and wet mass daily increments increased with larval age. Daily length increments showed a negative and poor relationship with long-term otolith growth. In contrast, DNA, protein and wet mass daily increments were positively correlated. Differences between observed and back-calculated otolith radius-at-age indicated that larvae with slow otolith growth were under represented in older age groups, suggesting the existence of growth-selective mortality. Recent otolith growth, estimated from the mean widths of the last six increments, increased with age and R . Individual RNA: DNA and protein: DNA ratios were correlated significantly, although weakly, with L _S and larval growth.     

Growth and otolith microstructure of cod (Gadus morhua L.) larvae

Cod larvae from Irish Sea stocks were reared under differentgrowth conditions, and the otolith growth and increment formationexamined in sagittae and lapilli. Otolith increments were firstdeposited around the time of hatching and increment counts,on average, reflected larval age. The growth rate of fish larvaereared in different sized tanks was significantly different(P < 0.001), but there was no detectable effect on incrementformation. Otolith size was independent of larval size for individuals<5 mm in length. In larvae >6 mm, larger, faster growingindividuals had larger and faster growing otoliths.     

Growth variability of juvenile skipjack tuna (<Emphasis Type="Italic">Katsuwonus pelamis</Emphasis>) in the western and central Pacific Ocean

We examined growth rates of juvenile skipjack tuna using otolith daily increment analysis to clarify geographic differences in early-life stage growth in the western and central Pacific Ocean (WCPO). We used a liner regression model to analyze the relationship between standard length (SL) and age (in days). The slope of growth model was significant difference between regions. There were rapid increases in the otolith mean daily increment width of juveniles at 7 days after hatching (DAH) and 10 DAH in the Western Pacific Warm Pool (WARM) and North Pacific Tropical Gyre area (NPTG), respectively. These periods correspond to the timing at which larvae complete their digestive-system development and start the piscivory. We found significant difference in logarithmic back-calculated SL between WARM and NPTG at 3 DAH (p?<?0.01). Mean growth rates until 10 DAH, when the larvae metamorphose into juveniles, were positively correlated with sea surface temperature (r?=?0.52). These results indicate that geographic difference in the growth of juvenile skipjack tuna caught in the WCPO in boreal winter cause in the larval stage, and that these differences are related to sea surface temperature.     

Is the marginal otolith increment width a reliable recent growth index for larval and juvenile herring?

Marginal otolith increment width analysis was performed on field‐collected larval and juvenile spring‐spawned herring Clupea harengus that experienced variable feeding conditions and high temperatures that were above the optimum for growth. Although drastic zooplankton biomass reduction had a significant effect on increment width, a delay of a few days in the otolith response was observed. More importantly, a very clear, positive temperature effect on marginal increment width was demonstrated in fish characterized by temperature independent somatic growth. These results indicate that under natural conditions it may be impossible to distinguish increment width changes related to variation in feeding conditions from changes caused by temperature fluctuations. Therefore, it was concluded that marginal otolith increment width analysis could not be used as a recent growth index ( I _G) for herring larvae and juveniles exposed to drastic temperature fluctuations. The implication of these results is significant not only for the use of marginal increments as a recent growth index, but also if growth rate backcalculation is to be used as a research method.     

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.     

Nutritional condition of larval milkfish,Chanos chanos,occurring in the surf zone

In order to clarify the nutritional conditions of larval milkfish in the surf zone, the following parameters were examined: 1) DNA and RNA content and RNA/DNA ratio of fed and unfed larvae collected from the surf zone and reared in the laboratory; 2) survival rate of the unfed larvae; and 3) total length, otolith increment counts and RNA/DNA ratio of wild larvae collected daily from the surf zone. The DNA and RNA content of the unfed larvae decreased, but increased in fed larvae. The RNA/DNA ratio decreased in unfed larvae, whereas in the fed larvae it decreased for the first three days after capture and increased thereafter. These results indicated that the values of DNA and RNA content and RNA/DNA ratio could be used as an indicator of nutritional condition of milkfish larvae after 6 days of starvation. Although total length of the wild-larvae did not show serial changes, their otolith increment counts showed continuous increases, indicating that the larvae sojourned in the surf zone for several days. In the same period, RNA/DNA ratios of the wild larvae decreased continuously, the ratios of larvae with fewer otolith increment counts being relatively higher than those of larvae with greater increment counts. Based on these results, the milkfish larvae remaining in the surf zone were concluded as being under insufficient nutritional conditions.     

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.     

The effect of temperature and somatic growth on otolith growth: the discrepancy between two clupeid species from a similar environment

Otolith growth rates of the early life stages of herring Clupea harengus ( n = 472) and smelt Osmerus eperlanus ( n = 348) collected in the Vistula Lagoon (Baltic Sea) during 1997–1999 were analysed. The larvae and early juveniles were not only collected in the same geographical area they were also of the same size (range 15–43 mm standard length, L _S), similar ages and were collected during the same seasons (May to July). Although the two clupeid species experienced very similar environmental conditions, there were significant discrepancies in the analysed relationships. The otolith growth of larval and juvenile smelt was very strongly related to somatic growth while temperature had a minor effect. In herring, the effect of somatic growth, although clearly visible and statistically highly significant, was of less importance than temperature. Furthermore, variation in the otolith size and L _S relationship was affected by temperature and somatic growth in both species, but the variance of otolith size at L _S was higher for herring than for smelt. Although growth backcalculation from otoliths can presently be recommended as an appropriate method for use with both smelt and herring (despite possibly lower precision and accuracy with the latter), other methods referring directly to short-term increment width changes ( e.g. marginal increment analysis) are recommended for smelt but not for herring.     

Nutritional condition of metamorphosing sole: spatial and temporal analyses

Sole Solea solea larvae were collected during five cruises in the Bay of Biscay in 1992 and 1993. The larval growth rate, triacylgycerol (TAG) and sterol (ST) content, and the width of the marginal otolith increments were determined on the same individual larva as indicators of nutritional condition. The TAG content increased during the ontogenetic larval development up to an elevated value corresponding to the end of metamorphosis. During metamorphosis, sole larvae continued to accumulate TAG and to increase in length. Seasonal and yearly variations of growth and nutritional condition of sole larvae at the onset of metamorphosis were more important than spatial variations. Analysis of larval growth showed that, during each cruise, the faster growing larvae were generally those with the highest TAG content (and TAG : ST ratio). In 1993, larvae began to metamorphose earlier and their growth (both larval growth and recent growth) were significantly higher than in 1992. Their relatively low nutritional condition, however, seemed to be the result of a low accumulation of TAG. Sole metamorphosis occurs without growth arrest and the majority of the larvae during this phase are judged to be in good nutritional condition (TAG : ST ratio > 1). In the Bay of Biscay, metamorphosis does not seem to be a critical period in the life cycle of the sole. It is suggested that larvae originating from different cohorts probably have the same chance of survival during or just after metamorphosis when they enter the benthic environment.     

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.     

Anastrepha ludens (Loew) (Diptera: Tephritidae) larvae irradiated at higher doses improve the rearing of two species of native parasitoids

Irradiation doses 40, 80, 120 and 160 Gy were used on 6-, 7-, 8- and 9-days-old Anastrepha ludens (Loew) (Diptera: Tephritidae) larvae. The larvae from the different age groups irradiated with different doses were exposed separately to Neotropical-native Doryctobracon crawfordi (Viereck), Utetes anastrephae (Viereck) and the Asian introduced Diachasmimorpha longicaudata (Ashmead) parasitoids (Hymenoptera: Braconidae). A significant increment in parasitoid emergence directly related to radiation increment on parasitoids D. crawfordi and U. anastrephae was observed. This effect was higher on irradiated young larvae; in D. longicaudata, emergence increment was related to age of larva but not with radiation doses. Similar results were obtained for sex ratio. Host larva weight increased with age, and irradiation had no effect on gaining weight of growing larvae. The host larval mortality 72 hr after exposition had an inverse relationship regarding to its age, although it did not have a negative effect as regards radiation doses. Immature stages of parasitoid/larva (>1 = superparasitism) were higher in 8-days-old larvae parasitized by D. Longicaudata, while in D. crawfordi and U. Anastrephae, superparasitism was absent (<1 immature stage per host larva). Superparasitism was not affected by increased radiation dose. No levels of melanin were detected as indicators of immunological reactions. However, these results are considered to be closely related to the lessening of these reactions due to irradiation. The positive relationship between emergence and irradiation dose to host larvae was present in native species D. crawfordi and U. anastrephae, but absent for exotic D. longicaudata. The data presented here are of great relevance for cost effective mass rearing of these parasitoids.     

果实大小对油茶象幼虫生长的影响

为了明确小果油茶果实大小对油茶象幼虫生长发育的限制作用,采用Logistic方程对油茶象老熟幼虫体质量与其寄主果实体积大小的关系进行了拟合.结果表明: 油茶象幼虫体质量随果实体积增大而增长,符合Logistic模型;油茶象幼虫体质量增长符合边际效应递减原则,可分为快速增长阶段(<3.216 cm³,每果1头;<4.747 cm³,每果2头)和渐进增长阶段(>3.216 cm³,每果1头;>4.747 cm³,每果2头);油茶象寄生的最小果实阈值为1.500 cm³(每果1头)或2.539 cm³(每果2头).明确了落果中油茶象老熟幼虫逃逸的时间格局,果实收集后幼虫逃逸数量逐天递减,逃逸高峰期集中在6:00—10:00,占43.9%,尤以7:00—8:00为甚,占21.1%;幼虫体质量越大,逃逸越早.寄主果实大小对油茶象幼虫生长发育具有限制作用,亲代雌虫选择大果实产卵是增加后代适合度的一种行为适应策略.