The effect of starvation on RNA: DNA ratios and growth of larval striped bass, Morone saxatalis

Hatchery reared larval striped bass, Morone saxatilis , 8-days-post-hatching were subjected to various feeding/starvation regimes over a period of 14 days.
Batches of larvae from each treatment were sampled over the 14-day period and subdivided for determination of notochord length and RNA:DNA ratio. The best growth was found in fully fed F1000 larvae (exposed to 1000 Artermia nauplii l⁻¹), which reached 8.2 mm after 11 days and 9.6 mm after 14 days. Starved animals after 11 days had notochord lengths of 4.9 mm. Growth curves from feeding-delayed larvae indicated that animals fed after up to 5 days starvation were capable of complete recovery. F100 larvae (exposed to 100 Anemia nauplii 1^−l) had a slower growth rate than F1000 larvae, reaching a notochord length of 7.3 mm after 14 days. RNA:DNA ratios over time closely followed notochord growth curves, with clear differences between starved, F100 and F1000 larvae being established after only 2 days. Equilibrium RNA:DNA ratios of 3.0 and 2.25 were established in F1000 and F100 larvae, respectively, 6.8 days after the beginning of the experiment. The average lag time between a change from the starved to the fed condition and a change in RNA:DNA ratio as determined by the divergence of the nucleic acid curve from the starved condition was 0.66 days.
In treatments where starvation followed various periods of feeding, larvae regressed in notochord length such that the final length at 14 days reflected the degree of feeding. RNA:DNA ratios in these animals again closely followed growth curves with a lag time of 0.81 days.
It was concluded that RNA:DNA ratios provided very accurate indices of growth in striped bass larvae which were highly sensitive to feeding status.     

Field evaluation by RNA/DNA ratios on post-release nutritional status of released and wild Japanese flounder Paralichthys olivaceus juveniles

A large-scale juvenile Japanese flounder (Paralichthys olivaceus) release-recapture experiment was undertaken to find the optimal release season by evaluating the nutritional status of released fish at different seasons during which food abundance was significantly different. Forty thousand fish were released at depths of 1.5 m for early-release (May 29, 1997) and 2 m for late-release (July 2, 1997) (42.1±3.5 and 40.9±4.2 mm body length, respectively) in an experimental field, Wakasa Bay, the Sea of Japan. Samples were taken, after the releases, at Wada beach at intervals of 1, 2, 3, 6, 10, 16 and 30 days after release (DAR), including pre-surveys before each release. Released fish recaptured from the two different release groups totaled 764; 467 from the early-release group (ER) and 297 from the late-release group (LR). A total of 1956 wild flounder juveniles were simultaneously collected (1041 ER, 915 LR). ER fish were subject to higher food availability and were exposed to less pressure from predation by smaller wild juvenile flounder. RNA/DNA ratios in ER juveniles were significantly higher than those of LR fish during all samples. Especially, RNA/DNA ratios in ER juveniles were higher than in wild juveniles from 3 to 50 DAR. In the LR group, the nutritional status of juveniles was relatively low in shallower water. These findings corresponded well with feeding incidence examined by coworkers. Mass release of hatchery-reared juveniles apparently reduced RNA/DNA ratio of the wild juveniles right after releasing. The present study showed that earlier release of hatchery-reared juvenile Japanese flounder with higher RNA/DNA ratio could increase the possibilities of survival right after release in the nursery ground, and that RNA/DNA ratio appeared to be a good tool in evaluating nutritional status of released juveniles as well as wild juveniles in Japanese flounder.     

Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvae

Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c . 17° C. Non-fed fish reached irreversible starvation at age 5 DAH. Non-fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non-fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non-fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two-thirds to three-quarters of the overall mortality (46–52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non-fed larvae accounted for about a third of the overall mortality (100%).     

Comparison of behavioural development between Japanese flounder (Paralichthys olivaceus) and spotted halibut (Verasper variegatus) during early life stages

Behavioural development was compared between two flatfish species (Japanese flounder and spotted halibut) from hatching to settlement (juvenile stage) in order to speculate on the ecology of their early life stages and to provide fundamental knowledge for improving seedling production techniques for stock enhancement. Fish were cultured under identical rearing conditions (500‐L tank maintained at 17.8 ± 0.4°C, 34 ppt, 10L : 14D light regime and an initial stocking density of 20 larvae L^?1). Behavioural observations were conducted at about 4‐day intervals from hatching to the juvenile stage. Fish were sampled randomly from the rearing tank, and one fish was transferred into a 250‐ml observation container. Behaviour was video‐recorded for 5 min without food and for an additional 5 min with live feed (rotifer or Artemia). All behavioural data were sorted according to eight developmental stages and compared among developmental stages and between species. The average standard length of the spotted halibut was significantly greater than that of the Japanese flounder in all developmental stages, while the development of Japanese flounder was faster than that of the spotted halibut. For Japanese flounder, feeding, swimming and Ohm‐posture (typical shivering behaviour observed during early life stages in flatfishes) frequency were highest before metamorphosis (mean ± SD; 1.0 ± 2.0 attacks min^?1, 24.0 ± 9.6 actions min^?1, 1.1 ± 1.1 counts min^?1, respectively). Spotted halibut expressed feeding behaviour frequently from the beginning of metamorphosis (3.6 ± 5.2 attacks min^?1), had relatively low swimming activity during all developmental stages, and showed a peak of Ohm‐posture frequency during the flexion stage (2.6 ± 1.0 counts min^?1).     

短期饥饿和再投喂对岩原鲤仔鱼生存生长以及RNA/DNA和RNA/蛋白质比率的影响(英文)

研究通过对岩原鲤仔鱼在饥饿和再投喂条件下其生存、生长率、RNA/DNA和RNA/蛋白质比率的测定,评估了仔鱼对饥饿的耐受能力和恢复能力。在(19.5±0.5)℃水温下,将岀膜后第16天的岩原鲤仔鱼随机分成6个组:1个持续投饲对照组,实验组分别禁食1、2、3、4、5d后再投喂,实验共进行10d。每天分别从各组取9尾鱼测定体重、体长、RNA、DNA、蛋白质含量。实验结果显示,饥饿处理组仔鱼存活率和以上各项生长指标均随饥饿时间的增加而下降,在恢复投喂后均表现不同程度的补偿生长,其中饥饿1、2、3d的仔鱼在恢复投喂后显示出完全补偿生长,几乎弥补了饥饿所产生的影响,平均终体重与对照组比较无显著差异。饥饿4、5d的仔鱼显示部分补偿生长,恢复投喂只少量减轻了饥饿的影响,平均终体重与对照组相比存在显著差异。饥饿1、2、3d的仔鱼和4、5d的仔鱼在恢复投喂后分别需要1—2d和4d时间才能达到与对照组无显著差异水平。仔鱼生长率变动范围从0.59%到8.00%WW/day,仔鱼RNA/DNA比率、RNA/蛋白质比率与生长率的回归方程为:GR=3.63RNA/DNA 1.74(R2=0.80)和GR=120.14RNA/Protein 2.33(R2=0.31),两种比率均与生长率呈显著线性相关,RNA/DNA比率对生长变化的拟合度更好。结果表明,仔鱼阶段食物缺乏很可能是影响岩原鲤仔鱼存活、生长的主要因素。RNA/DNA更适合作为评定岩原鲤仔鱼营养条件和生长的指标。     

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.     

Identification and differential expression of microRNAs during metamorphosis of the Japanese flounder (Paralichthys olivaceus)

Background

MicroRNAs (miRNAs) are a class of endogenous small non-coding RNAs of 20–25 nucleotides that play a key role in diverse biological processes. Japanese flounder undergo dramatic metamorphosis in their early development. The metamorphosis is characterized by morphological transformation from a bilaterally symmetrical to an asymmetrical body shape concomitant with extensive morphological and physiological remodeling of organs. So far, only a few miRNAs have been identified in fish and there are very few reports about the Japanese flounder miRNA.

Methodology/Principal Findings

Solexa sequencing technology was used to perform high throughput sequencing of the small RNA library from the metamorphic period of Japanese flounder. Subsequently, aligning these sequencing data with metazoan known miRNAs, we characterized 140 conserved miRNAs and 57 miRNA: miRNA* pairs from the small RNA library. Among these 57 miRNA: miRNA* pairs, twenty flounder miRNA precursors were amplified from genomic DNA. We also demonstrated evolutionary conservation of Japanese flounder miRNAs and miRNA* in the animal evolution process. Using miRNA microarrays, we identified 66 differentially expressed miRNAs at two metamorphic stages (17 and 29 days post hatching) of Japanese flounder. The results show that miRNAs might play a key role in regulating gene expression during Japanese flounder metamorphosis.

Conclusions/Significance

We identified a large number of miRNAs during flounder metamorphosis, some of which are differentially expressed at two different metamorphic stages. The study provides an opportunity for further understanding of miRNA function in the regulation of flounder metamorphosis and gives us clues for further studies of the mechanisms of metamorphosis in Japanese flounder.     

Responsiveness of selected condition measures of herring, Clupea harengus, larvae to starvation in relation to ontogeny and temperature

A laboratory experiment was performed to study the responsiveness of selected condition measures to starvation in herring, Clupea harengus, larvae in relation to temperature and ontogeny. The larvae at two intervals of development, i.e. stage 1 larvae with initial exogenous feeding and stage 2 larvae with established feeding prior to notochord flexion, were reared at three temperatures (5, 8 and 11°C) and subjected to sub-lethal durations of starvation. Temporal changes in standard length, dry weight, DNA concentration (% of dry weight), RNA concentration (% of dry weight), Fulton's condition factor (CF) and RNA/DNA were assessed and compared with fed controls. Starvation led to decreases in dry weight, CF, RNA concentration and RNA/DNA, while it led to an increase in DNA concentration. Higher responsiveness to starvation was observed at higher temperatures, and the magnitude of the changes was higher in stage 2 larvae. The shortest latency in starvation response was found with respect to RNA/DNA which was length independent in the size range studied. RNA/DNA was also significantly related to average DNA growth rate, and the model for DNA growth rate was, SGRDNA=4.49 RNA/DNA + 7.14 T – 0.42 T2 – 37.5 ; n=32, r2=0.85, p < 0.001). While the model seemed to adequately represent the average temperature dependent DNA growth, a relatively low classification success made it unsuitable for depicting individually starving larvae. Critical levels in DNA concentration can be used (2.2% for stage 1 larvae, 2.9% for stage 2 larvae) to differentiate starving larvae (after 3 – 5 days) from feeding larvae. RNA/DNA was the most sensitive and suitable condition index studied in detecting early starvation of herring larvae.     

A review and assessment of the potential use of RNA:DNA ratios to assess the condition of entrained fish larvae

In rivers, lakes, and other aquatic systems throughout the world, intake pipes withdraw huge volumes of water for industrial purposes, including power plant cooling. During this process, large numbers of small-bodied, early life-stages of fish are pulled into pipes (i.e., entrained) and may be subjected to physical, thermal and chemical stress. As a result of such entrainment, these organisms can suffer direct or indirect mortality. However, given that the vast majority of larval fish are likely to die during early life due to natural processes, it is not obvious that entrainment-related mortality will have a strong influence on subsequent adult population sizes. The ability to evaluate if larval fish are dead on arrival, moribund, or in poor condition (i.e., likely to die through natural processes) at the time of entrainment could shed light on likely population-level impacts. To this end, we review the potential use of RNA:DNA ratios to index condition of entrained larval fish. Through a meta-analysis of published research studies, we demonstrate that RNA:DNA ratios of larval fish are responsive to starvation stress, with effect size increasing with duration of starvation. We relate these results to a surrogate measure of irreversible long-term negative impacts to fish populations, and demonstrate that the timescale over which RNA:DNA ratios respond to stress may not be long enough to reflect before-and-after entrainment stress. We also highlight the diverse factors contributing to variation of RNA:DNA ratios, including methodological, ontogenetic, and thermal influences. We believe that the need to account for these influences when comparing among RNA:DNA values limits the utility of broadly using RNA:DNA ratios to evaluate entrainment effects. However, the method shows promise as a quick and efficient means of determining fish condition and, used in proper context (e.g., specific to a given set of environmental conditions; in conjunction with other assessment techniques), may provide a powerful tool in assessing the effects of entrainment on fish populations. Assuming that researchers can account for sources of background variation, RNA:DNA analyses may be most useful for assessing the condition of fish larvae susceptible to entrainment (i.e., physically in the vicinity of the water intake) and/or evaluating whether fish larvae are likely to die from natural processes independent of entrainment.     

Use of multivariate analysis to assess the nutritional condition of fish larvae from nucleic acids and protein content

The nutritional condition of turbot larvae (Scophthalmus maximus) was assessed by a multivariate analysis with DNA, RNA, and protein content as input variables. Special attention was given to the time that feeding began and to the timing and duration of starvation. The combination of the principal components analysis and the stepwise discriminant analysis, both techniques of multivariate analysis, made it possible to allocate the larvae into groups that were defined and identified based on similarities in developmental stage and nutritional condition. The developmental stage was mostly determined by the input variables DNA and protein content, while nutritional condition was determined by the RNA content. In the period studied, the more developed larvae were less resistant to starvation. Furthermore, when initial feeding was delayed as little as 6 h, the variables analyzed were markedly changed, and the effect on the deprived larvae was found to be equivalent to a 3-day delay in development-when compared with the larvae fed immediately after mouth opening. Through this technique, new samples of larvae with unknown history might be classified into groups, using their DNA, RNA, and protein content as input values in the defined classification functions. Results were compared to those obtained using RNA/DNA and RNA/dry weight indices, and the multivariate method was considered to be more sensitive and to provide extra information about larval nutritional history and development.     

Infection with Edwardsiella tarda causes hypertrophy of liver cells in the Japanese flounder Paralichthys olivaceus

To study the direct cause of liver enlargement in the Japanese flounder Paralichthys olivaceus infected with Edwardsiella tarda, the fish were challenged with E. tarda and reared without feeding. The liver of fish exposed to the bacteria was markedly enlarged compared to that of the controls while no severe histopathological change appeared in the organ during the experiments. No notable difference was observed in the crude fat, glycogen, and water content of the liver between challenged and control fish. The size of liver cells and nuclei of the challenged fish was apparently larger than that of the controls. Analysis of crude DNA in the liver suggested that the number of liver cells of starved control fish significantly decreased during the experiment while that of the challenged fish was maintained at a level of the initial control. RNA/DNA ratio of the liver of challenged fish clearly increased while it decreased in the control fish during the experiment. These observations suggest that liver enlargement of flounder infected with E. tarda, at least in the early stage of infection, is not a result of any readily observable histopathological changes and that E. tarda infection causes hypertrophy of the cells, as well as preventing decrease in liver cell number.     

Feeding behaviour of Japanese flounder larvae under laboratory conditions

Tank–reared Japanese flounder larvae, Paralichthys olivaceus , had a major feeding peak in the morning and a secondary peak in the afternoon throughout the larval development, with light being the primary factor regulating their feeding activity. The larvae consumed rotifers in preference to Artemia for up to 10 days, after which the food preference shifted to Artemia . Feeding rates of the larvae prior to 10 days post–hatch depended on prey density, but in the old larvae, feeding rates were independent of prey density. Maximum feeding rate occurred at 19° C. The occurrence of the attack posture, after its onset at first feeding (2 days post–hatch), increased up to 25 days, began to decrease when the larvae prepared to settle down, then disappeared after settlement. The occurrence frequency of the attack posture was positively related to fish density, but inversely related to starvation duration, and occurred most frequently at 19° C. This posture depended on prey density in larvae prior to 10 days post–hatch, but became independent of prey density as the larvae developed. It was obvious that, for flounder larvae, attack posture was a behavioural character closely related to feeding and subject to larval development and environmental factors.     

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.     

Embryonic and larval staging of summer flounder (Paralichthys dentatus)

Early development of flatfishes such as the summer flounder Paralichthys dentatus (Pleuronectiformes) has not been extensively documented, largely because of a dearth of material; however, the recent expansion of flatfish aquaculture has made embryos of P. dentatus readily available for developmental studies. We divide development of P. dentatus embryos and larvae into two main periods, pre- and posthatching, and assign stages within each of those primary divisions. Stages from fertilization to hatching loosely follow the general teleost staging scheme suggested by Shardo ([1995] J Morphol 225:125-167); stages from hatching through metamorphosis are aligned with the series used for Japanese flounder, P. olivaceus (Minami [1982] Nippon Suisan Gakkaishi 48:1581-1588; Fukuhara [1986] Nippon Suisan Gakkaishi 52:81-91). Although length, width, and age may serve as approximate indicators of developmental progression in summer flounder, these characteristics are too variable to form the sole basis of a staging table. Therefore, we define stages by morphological criteria drawn from the development of the jaw apparatus and digestive system, eye migration, and notochord tip flexion. Examination of these morphological features in hatched larvae allows accurate and consistent assessment of developmental stage despite variation in timing and size. The staging scheme for flounder embryonic and larval development presented here should facilitate both experimental and comparative research on summer flounder and other flatfish species.     

Ontogenic changes in tolerance to hypoxia and energy metabolism of larval and juvenile Japanese flounder Paralichthys olivaceus

Changes in tolerances to hypoxia and sodium azide, an indicator of cellular respiration, and activities of various energy metabolism-related chemical components were studied in Japanese flounder Paralichthys olivaceus during its early life stages from 3.5 to 20.5 mm in total length (TL). They showed flexion stage around 10.4 mm TL. Lethal levels of hypoxia increased with growth from 3.5 to 8 mm total TL, and the levels remained high in larvae, until 10.4 mm TL, decreased significantly thereafter. The 50% lethal concentration of sodium azide temporarily increased at 4.5 mm TL, diminished drastically between 4.5 and 10.4 mm TL, and then increased again in post-flexion larvae. Cytochrome c oxidase activity was highest in larvae around flexion, at 10.4 mm TL, and subsequently decreased. In post-flexion larvae at 13.0 mm TL, lactate dehydrogenase (LDH) and creatine kinase activities increased; LDH activity decreased at the juvenile stage. The adenosine triphosphate content and energy charge in fish were consistently higher in the larval stage than in the juvenile stage. These results indicated that, from just before flexion to the post-flexion stage, the energy metabolism of larvae is higher due to activated aerobic and subsequent anaerobic metabolism for metamorphosis; as a consequence, hypoxia tolerance in fish is the lowest during the increase of aerobic metabolism just before and around flexion.     

Loss and gain of the juvenile rudiment and metamorphic competence during starvation and feeding of bryozoan larvae

SUMMARY In many animals, larval structures and juvenile rudiments develop independently. One advantage of this independence is that juvenile rudiments can be expended as a nutrient reserve or for energy conservation. When bryozoan cyphonautes larvae were starved, structures required for settlement and metamorphosis shrank. When the larvae were again fed, these structures grew back. Starvation reduced the size of both the internal sac, a rudiment of postlarval juvenile structures, and the pyriform organ, which functions in sensing and crawling on the substratum at settlement. In contrast, starvation affected neither the size of the larval shell nor the lengths of the ciliary bands used in swimming and feeding. Starved larvae that had reduced the pyriform organ and internal sac did not metamorphose in response to stimuli from a laminarian alga. The laminarian alga did stimulate metamorphosis of the same larvae after renewed feeding, when the larvae had regrown these structures. Thus starved larvae expended body parts needed for settlement and metamorphosis when food was scarce while retaining structures for feeding, swimming, and defense. Starved larvae thereby retained the capacity to regrow structures needed for settlement and metamorphosis when they again encountered food. Advantages from expendable juvenile rudiments may enhance selection for their being developmentally distinct from structures for larval swimming and feeding.     

Comparison of nutritional status of field and laboratory reared Balanus amphitrite Darwin (Cirripedia: Thoracica) larvae and implication of starvation

Experiments were carried out to evaluate the influence of rearing temperature and food concentration (20 and 30 °C, 1×10⁵ and 2×10⁵ cells ml⁻¹) on the starvation threshold and nucleic acid content of the larvae of Balanus amphitrite. The larvae were also field-reared using micro-enclosures. Laboratory-reared larvae were larger in size than the field-reared larvae. An increase in size, DNA content and instar index of the starved II instar larvae was observed indicating that the absence of food may not be fatal to this early instar. The temperature at which larvae were raised and the food concentration had variable influence on the capacity to withstand starvation. Exposure to increased temperatures during starvation eliminated the effect of doubling food concentration during their feeding period prior to starvation. The larvae reared at 20 °C had comparatively lower nucleic acid content. The laboratory-reared larvae had ca. 1.7 times greater RNA:DNA ratio than larvae raised at comparable temperature in the field.     

Assessment of the nutritional status of field-caught larval Pacific bluefin tuna by RNA/DNA ratio based on a starvation experiment of hatchery-reared fish

RNA/DNA ratio is a useful and reliable indicator of the nutritional status of fish larvae and juveniles. In order to assess the nutritional status of field-caught larval Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel), starvation experiments of hatchery-reared larvae were conducted and changes in the RNA/DNA ratio of fed and starved larvae were analyzed. Starvation experiments were conducted every 3 days after first feeding. The survival rate of Pacific bluefin tuna larvae ranged 10-50% after 1 day of starved conditions and growth retardation was observed immediately. These results suggest that Pacific bluefin tuna larvae have a very low tolerance to starvation. The RNA/DNA ratios of fed larvae were approximately 2.0-4.0. On the other hand, the value of starved larvae significantly decreased to 1.0-3.0. The nutritional status of 3 cohorts of field-caught tuna larvae collected in the northwestern Pacific Ocean was examined based on the value of the RNA/DNA ratio of the 1 day starved larvae. 4.35-25.77% of the cohorts were regarded as the “starving condition”, which was negatively correlated to the ambient prey densities. These findings suggest that the nutritional condition of larval Pacific bluefin tuna was influenced by the ambient prey density, and starvation itself and starvation-induced predation could greatly contribute to mortality in the larval period of Pacific bluefin tuna.     

饥饿和再投喂对草鱼鱼种生物化学组成的影响

分析了饥饿１５天和再投喂２１天的草鱼鱼种肝脏和肌肉生物化学组成的变化，结果表明：（１）饥饿降低白肌ＲＮＡ／ＤＮＡ比值，蛋白质含量和肝脏ＲＮＡ／ＤＮＡ比值，使肝脏蛋白质含量升高，再投喂后，肝脏ＲＮＡ／ＤＮＡ比值，蛋白质含量和白蛋白质含量均恢复至正常投喂组水平，白肌ＲＮＡ／ＤＮＡ比值升高并显著高于正常投喂组水平；（２）饥饿状态下，肝脏和肌肉的脂类含量降低，水含量升高，再投喂后，肝脏和肌肉的脂类含量升高