Early development of the digestive tract of cod larvae, Gadus morhua L., during start-feeding and starvation

Cod larvae, Gadus morhua L., were reared in the laboratory and released to a large marine enclosure 4 to 5 days after hatching (6–8° C). The development of the digestive system was studied until day 24 after hatching. Morphological investigations of the jaw apparatus and the digestive tract showed that the larvae are able to absorb ingested food well before exhaustion of the yolk sac. The foregut, and especially the midgut, were particularly active in lipid absorption, and the hindgut was characterized by pinocytotic activity. Duhng the first days of feeding, no distinct prey organisms were observed in the gut, and signs of food absorption in the epithelial cells of the gut were sparse.A distinct red fluorescence, restricted to the hindgut, was observed from day 11 to day 19. On the basis of changes in absorptive pattern in the gut we suggest that changes in digestive and absorptive abilities, as well as in nutritional needs, take place around days 15–17 after hatching.
In starved larvae, signs of degeneration of the gut tissue were first visible in the foregut. By day 9 after hatching, microvilli was degenerated to such an extent that the ability to absorb food must have been severely restricted. If larvae are starved longer than this, they will probably not survive.     

Ontogenetic changes in RNA,DNA and protein contents of Chinese loach,Paramisgurnus dabryanus (Dabry de Thiersant, 1872), larvae and juveniles

The changes in nucleic acid‐based indices and protein variables of Chinese loach, Paramisgurnus dabryanus, larvae and juveniles from hatching to 60 days after hatching (DAH) were conducted to assess its growth potential. The nucleic acid contents were analysed using a UV‐based method (n = 3, rearing temperature 24.4 ± 0.4°C, dissolve oxygen 7.1 ± 0.5 mg L^?1, pH 7.9 ± 0.4). Ribonucleic acid (RNA) concentration significantly decreased from 2 to 5 DAH, then increased rapidly until 10 DAH, declining slightly thereafter. Deoxyribonucleic acid (DNA) concentration increased 2–5 DAH, decreased until 9 DAH, slightly increased again around 26 DAH, and then declined to a relatively stable level. Both RNA‐DNA and protein‐DNA ratios showed a statistically obvious relationship with growth rates. A significantly positive relationship was found between RNA‐DNA ratio and growth rates during the early life stage of Chinese loach. According to the results, growth of Chinese loach is characterized by rapid hyperplasia from hatching through completion of the yolk‐sac stage followed by continued rapid hyperplasia combined with increasing hypertrophy after feeding commences. The stage preceding 17 DAH of Chinese loach P. dabryanus is presumed to be critical for its survival and growth at 24°C.     

The 30kP protease A responsible for 30-kDa yolk protein degradation of the silkworm, Bombyx mori: cDNA structure, developmental change and regulation by feeding

We have cloned and sequenced the cDNA encoding the major component (43-kDa peptide) of 30kP protease A which selectively hydrolyzes 30-kDa yolk proteins of the silkworm, Bombix mori. The deduced amino acid sequence consisted of 318 amino acids and shared sequences conserved in many serine proteases. Northern blot analysis using the cDNA as probe revealed that 43-kDa peptide mRNA began to rise at the last phase of embryogenesis and reached a maximum level at larval hatching. This level was maintained with some fluctuations throughout post-embryonic development. The concentration of 43-kDa peptide increased greatly toward larval hatching coinciding with the changing pattern of mRNA. When larvae were fed, the peptide concentration abruptly decreased and remained near zero throughout post-embryonic development. The decrease in peptide concentration did not occur, however, when the hatched larvae were starved. Thus, the nutritional shift from endogenous yolk to exogenous food plays a key role in 30kP protease A elimination from neonate larvae.     

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.     

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.     

Evaluating the nutritional condition of individual whitefish (Coregonus spp.) larvae by the RNA/DNA ratio

Larvae of Coregonus spp. were reared in the laboratory under different temperature (4, 6 and 8°C) and feeding conditions ( ad libitum , limited, with starvation intervals). Their RNA/DNA ratios were determined with a highly sensitive fluorescence technique. After resorption of their yolk reserves (about 2 weeks after hatching), well fed larvae (RNA/DNA >2.5) could be significantly distinguished from larvae reared under limited food supply (RNA/DNA < 2.5), both at the 6 and 8°C levels. At 4°C, no differences due to the feeding regime were found. During a second series of experiments, larvae were affected by an intestinal disease, which was caused by the ingestion of unsuitable copepod plankton. This disease provoked high mortality, decreased growth and RNA/DNA ratios which were almost as low as in temporarily starved larvae from the first series. Coregonid larvae sampled in Lake Constance during spring 1990 showed RNA/DNA ratios which were unexpectedly low when judged on the basis of mean body length and average ambient temperature. It was obvious from macroscopic observations that some of these wild larvae were severely attacked by the intestinal disease. The low RNA/DNA ratios in field samples are, therefore, interpreted as a sublethal result of this disease.     

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。     

Development of bile salt-dependent lipase in larval turbot

Pancreatic bile salt-dependent lipase (BSDL) was present with 0·5 μg BSDL larva⁻¹ from hatching in turbot larvae. The enzyme content increased during the yolk sac phase to 1·1 μg BSDL larva⁻¹. This suggests that larval turbot are able to digest lipids from the start of exogenous feeding. The BSDL synthesis was stimulated first by food about 5 days after the onset of first feeding. The content per larva increased exponentially in fed larvae to 20 μg BSDL larva⁻¹ on day 23 after hatching and decreased in starved larvae. In contrast, the specific content decreased during the first feeding phase, meaning that smaller larvae had a higher content of enzyme related to their biomass than did bigger larvae.     

Rates of growth and protein synthesis correlated with nucleic acid content in fry of rainbow trout, Oncorhynchus mykiss: effects of age and temperature

Groups of recently hatched fry of rainbow trout, Oncorhynchus mykiss were maintained in the laboratory in order to investigate the effects of age, ration level and temperature on whole body growth, nucleic acid concentrations, protein synthesis rates and enzyme activities. In fry of up to 30 days after hatching, which were feeding but still had some yolk sac, no significant change in mean RNA concentration was observed with ration level. In older fry of 50 days or more, when the yolk sac was completely absorbed and exogenous feeding fully established, the concentration of RNA was correlated with the rate of protein growth. RNA concentrations and activities of citrate synthase and lactate dehydrogenase were significantly different between fed and starved fry. As water temperature was raised (from 5 to 15° C), higher rates of protein growth were brought about by an increase in the rate of protein synthesis and also by increased efficiency of retention of synthesized protein (reduced protein turnover). In fed fry, no change in RNA concentration was found with increasing temperature, while the amount of RNA per cell (RNA: DNA) decreased, indicating that increased rates of protein synthesis were due to increased RNA efficiency.     

Growth and respiration of embryos and larvae of the rabbittish Siganus randalli (Pisces, Siganidae)

Growth and respiration of larval rabbitfish from Guam were examined. Larvae were reared from eggs in 2- to 10-ton tanks and were fed rotifers, Anemia , and artificial feed in succession as development proceeded through metamorphosis. Growth in length was rapid during the 12 h after hatching, then slowed until the larvae began to feed. The yolk sac was usually absorbed by 36 h after hatching. Rates of respiration of larvae and eggs were determined with a dissolved oxygen electrode at various times through development. Larval metabolism increased steadily during the embryonic stages culminating in a metabolic burst immediately after hatching. Respiration rates remained relatively stable from shortly after hatching until the onset of exogenous feeding, after which respiration rates increased with larval size. The respiration rates of post-yolk-sac larvae scaled isometrically with larval dry mass. Daily growth of feeding larvae was 27 to 28% of larval dry mass.     

Developmental change in RNA: DNA ratios of fed and starved laboratory-reared Japanese flounder larvae and juveniles, and its application to assessment of nutritional condition for wild fish

Starved Japanese flounder Paralichthys olivaceus larvae were characterized by relatively lower levels of RNA content throughout their early life stages. Significant differences in the RNA: DNA ratios were found between fed and starved fish, and appeared to increase as starvation proceeded. Ontogenetic changes in RNA: DNA ratios were clearly observed during metamorphosis, especially decreasing during the period from the late-metamorphic to postmetamorphic stages. The criteria established from these laboratory experiments, were applied to the nutritional condition of wild larvae and juveniles collected in Wakasa Bay, Sea of Japan in 1994 and 1995 by measuring RNA and DNA content. Starved fish were mainly found in stage I (settling stage) fish during the late season of settlement in 1995. This suggests that starvation could be associated with settlement in Japanese flounder.     

Ontogenetic- and condition-related effects of starvation on responsiveness in herring larvae (Clupea harengus L.) during repeated attacks by a model predator

The escape behaviour of fed and food-deprived herring larvae (20-30 mm SL) was studied during repeated attacks with a glass probe in order to investigate the causal mechanisms of starvation-induced changes in reaction to predators. Two experiments were set up: one where the fed and starved larvae were of the same age but of different sizes and one with groups of similar size but different ages. Biochemical and morphological condition measures described the condition of individual larvae. Starved larvae showed a lower responsiveness than fed larger larvae of the same age, and the responsiveness in this experiment decreased with decreasing nutritional status of the larvae. However, starved larvae that were of the same size but older than fed larvae showed a higher responsiveness, which could be explained by differences in development of sensory systems. A combination of condition and developmental factors thus explained the differences between starved and fed larvae. Both starved and fed larvae showed decreasing responsiveness over time with repeated attacks with no difference between starved and fed larvae in the relative change over time. The results emphasise the importance of taking into account individual age and/or development when the nutritional condition of wild-caught larvae is incorporated in survival models.     

Developmental and nutritional regulation of the messenger RNAs for fatty acid synthase,malic enzyme and albumin in the livers of embryonic and newly-hatched chicks

Summary The mRNAs for fatty acid synthase and malic enzyme were almost undetectable in total RNA extracted from the livers of 16-day old chick embryos. Both mRNAs increased in abundance between the 16th day of incubation and the day of hatching. In neonates, fatty acid synthase mRNA level was dependent on nutritional status, increasing slowly if the chicks were starved and rapidly if they were fed. The abundance of malic enzyme mRNA decreased in starved neonatal chicks and increased in fed ones. When neonates were first fed and then starved, starvation caused a large decrease in the abundance of both mRNAs. Conversely, feeding, after a period of starvation, resulted in a substantial increase in both mRNAs. The relative abundances of fatty acid synthase and malic enzyme mRNAs correlated positively with relative rates of enzyme synthesis. Thus, nutritional and hormonal regulation of the synthesis of these two lipogenic enzymes is exerted primarily at a pre-translational level.The abundance of albumin mRNA decreased significantly between the 16th day of incubation and the day of hatching but did not change thereafter in fed or starved chicks. The relative stability of albumin mRNA levels after hatching attests to the selectivity of the nutritional regulation of fatty acid synthase and malic enzyme mRNAs. The decrease in albumin mRNA which occurred between 16 days of incubation and hatching contrasts with the increase in albumin mRNA sequences which occurred during late gestation in the fetal rat (20). High levels of albumin in the chick embryo may be related to the lack of an analogue of mammalian alpha-fetoprotein in birds.Abbreviations PIPES piperazine-N,N-bis (2 ethanesulfonic acid) - SDS sodium dodecyl sulfate Postdoctoral Fellow of the Medical Research Council of Canada.     

LC–MS/MS-Based Metabolome Analysis of Biochemical Pathways Altered by Food Limitation in Larvae of Ivory Shell, <Emphasis Type="Italic">Babylonia areolata</Emphasis>

Ivory shell, Babylonia areolata, is one of the commercially important mariculture species in China and South East Asia. Survival varies in the artificial hatching and larval rearing of B. areolata. Food deprivation may be involved in rearing mortality, and so, a better understanding of how larvae respond and adjust to starvation is needed. In this study, the metabolite profiles of newly hatched larvae with yolk (I), larvae with yolk exhaustion (II), larvae suffering 24 h starvation after yolk exhaustion (III), and larvae fed with exogenous nutrients after yolk exhaustion (IV) were analyzed by LC–MS/MS. Principal component and cluster analyses revealed differential abundance of metabolite profiles across groups. When compared to metabolite levels of the I group, significantly up-regulated metabolites included polyunsaturated fatty acids, phospholipids, nucleotide, amino acids, and their derivatives were found in the II group, indicating that organisms relied predominantly on glycerophospolipid metabolism and protein-based catabolism for energy production during this stage. During starvation after yolk exhaustion, the levels of all energy related metabolites were significantly reduced, but an increase in products of purine and pyrimidine metabolism indicated an insufficient energy supply and an increase in cellular disintegration. Larvae fed exogenous nutrients can have significantly improved metabolism compared to starved larvae. These findings suggest that metabolomics, using LC–MS/MS, can be used to assess the physiological status and food-affected metabolic changes affecting B. areolata larvae.     

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%).     

First feeding and subsequent growth performances in piscivorous larvae of Chinese perch Siniperca chuatsi (Perciforms: Sinipercidae)

The success of first feeding is influenced by many factors, such as prey availability, and is critical to subsequent larval growth performances. To test the advantages of prey exposure before complete yolk absorption in piscivorous larvae, feeding incidence and specific growth rate were longitudinally measured in Chinese perch Siniperca chuatsi larvae first fed at different ages. The results showed that Chinese perch larvae were able to capture live piscine prey at 4 DAH (days after hatching), 1 day before complete yolk absorption. The feeding incidence and specific growth rate were higher in larvae first fed at 4 DAH than in larvae first fed at 5 or 6 DAH. These results indicate that prey exposure experience can facilitate the onset of first feeding, and that successful exogenous feeding, even before complete yolk absorption, is important for growth performances of piscivorous fish larvae.     

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.     

Morphological and behavioural development of halibut, Hippoglossus hippoglossus (L.) larvae

Live yolk-sac halibut, Hippoglossus hippoglossus (L.) larvae from rearing experiments at Austevoll Aquaculture Station, Norway, were examined from hatching to past first feeding for developmental morphology and behaviour. The findings include development of the respiratory and circulatory organs, eye pigmentation, mouth formation, organs of the digestive system and the process of yolk absorption, as well as swimming speed and activity levels.
A stomodeum is not present at hatching although drinking is possible through a pair of branchial pits which gradually develop into the operculum and gill basket. The mouth normally opens slowly, the gape being restricted by a transverse septum until bones are formed. The amount of time spent swimming varies from less than 15% of the observation period during the first 2 weeks after hatching to between 70 and 100% around the seventh week after hatching, when individual differences become more apparent. Larvae generally react with a burst of swimming when two come into contact. Speed and duration of swimming seems to be correlated with development of eye pigment, heart size and fin formation. The yolk-sac period is divided into four stages.     

Feeding, morphological changes and allometric growth during starvation in miiuy croaker larvae

We investigated the effects of the timing of first feeding (larvae in F0, F1, F2, F3 and S were first fed on day 3, 4, 5, 6 days after hatching (DAH) and unfed, respectively) on feeding, morphological changes, survival and growth in miiuy croaker larvae at 24°C. The fed larvae initiated feeding on 3 DAH and reached point of no return (PNR) on 6 DAH. Larvae in F0 and F1 groups survived apparently better than F2 group at the end of the experiment on 36 DAH. High larval mortality occurred from 3 to 7 DAH in all feeding groups, accounting for 40% (F0, F1 and F2 groups) to 90% (F3 and S groups) of the total mortality. Larvae in F0 and F1 groups grew better than F2 group throughout the experiment. Eye diameter, body height, head height and mouth gape of the first feeding larvae were more sensitive to starvation than other morphometrics and could be used as indicators for evaluating their nutritional status. Results indicated that delayed first feeding over 1 day after yolk exhaustion could lead to poor larval survival and growth. To avoid starvation and obtain good growth in culturing, larvae feeding should be initiated within 1 day after yolk exhaustion at 24°C.