The physiology of digestion in fish larvae

Synopsis The acquisition, digestion, and assimilation of food is critical for the growth and survival of fish larvae; a fish larva either grows or it perishes. Fish larvae are characterized by digestive systems and diets that differ from adults. Larvae undergo a pattern of trophic ontogeny, changing diet with increasing size, and these changes result in differences in digestive requirements. At first feeding, the larval alimentary canal is functional, but is structurally and functionally less complex than that of adults. The larval alimentary canal remains unchanged histologically during the larval period before transformation. During transformation, major changes that result in the development of the adult alimentary canal occur. The ontogeny of the alimentary canal differs in different taxa, and experimental evidence suggests that functional differences exist as well. Assimilation efficiency may be lower in larvae than it is in adult fishes, due to a lack of a morphological and functional stomach in larvae, but the question of improving assimilation efficiencies during larval development before transformation remains unresolved.     

Digestion of Pollen Components by Larvae of the Flower-Specialist Bee Chelostoma florisomne (Hymenoptera: Megachilidae)

Pollen digestion in larvae of the solitary bee Chelostoma florisomne (Megachilidae), a pollen-specialist (oligolectic) species on Ranunculus spp. (Ranunculaceae), was investigated using histological techniques. Serial sections from the anterior-, median-, and posterior-midgut/hindgut regions of the larval alimentary canal were selectively stained and examined for disappearance of lipids, proteins, and carbohydrates from ingested Ranunculus pollen grains. During digestion, pollen contents were observed to gradually extrude through the grain apertures. Most of the digestion of lipids and proteins occurred in the anterior- and median-midgut, whereas carbohydrates disappeared more slowly and mainly in the median- and posterior-midgut. In the hindgut, pollen comprised mainly empty exine shells, which were crushed and often broken, suggesting that some components of the wall are degraded during digestion, causing collapse of the outer, chemically resistant wall layer (exine). Lipids were completely digested, but small quantities of proteins and carbohydrates were often still present in grains in the posterior midgut/hindgut. The pollenkitt appeared to be completely absorbed, with none evident in the posterior midgut or in larval feces. The findings indicate that this oligolectic bee has the digestive equipment necessary to effectively remove and absorb the nutrients present in the pollen of its restricted food source. Comparison with similar studies in adult honey bees suggests that differing digestive abilities might be an underlying factor in pollen specialization in bees.     

Specific features of digestive function development in larvae of some salmonid fish

We studied the activities of digestive enzymes responsible for the digestion of food carbohydrate and protein components in plant-eating fish at various stages of larval development. The activities of all digestive enzymes tend to rise during larval development. Species specific features of the alimentary canal functioning have been described.     

Specific Features of Digestive Function Development in Larvae of Some Salmonid Fish

We studied the activities of digestive enzymes responsible for the digestion of food carbohydrate and protein components in plant-eating fish at various stages of larval development. The activities of all digestive enzymes tend to rise during larval development. Species specific features of the alimentary canal functioning have been described.     

From the anther to the proctodeum: Pear (Pyrus communis) pollen digestion in Osmia cornuta larvae

Modifications of the pollen grains of Pyrus communis Linneaus that occur during the digestion by Osmia cornuta (Latreille) larvae were studied histochemically. We compared the features of the pollen grains found in the anthers, in the larval cell provisions and in the alimentary canal of the 5th instar larvae. Modifications were already evident in the provisions and consisted of protoplast protrusions through the apertures and a decrease in the number of starch-containing pollen grains. After pollen grains were ingested by the larvae, the protoplast appeared retracted from the pollen wall. Pollen digestion began in the anterior part of the midgut, where we observed: (1) disorganised intine at the apertures; (2) disappearance of DAPI staining of nuclear pollen DNA; (3) fewer pollen grains containing starch than in the anthers; (4) some empty pollen grains. Pollen grains in the proctodeum appeared extremely compressed and crushed. Some grains appeared to be unaffected by the digestive process. We hypothesise that the protrusion of the intine and of the protoplast from the apertures in bee provisions could be considered a kind of pre-treatment necessary to initiate the digestion process in the larval alimentary canal.     

Development of the digestive system of Argentine hake,Merluccius hubbsi,larvae

The Argentine hake Merluccius hubbsi is an important fishery resource of the Southwestern Atlantic Ocean and it is also a potential species for cultivation. In this work, the digestive system development in field-caught hake larvae was studied using histological and histochemical approaches. The digestive tract of larvae was divided into: oropharyngeal cavity (OPC), esophagus, stomach (that develops in the preflexion stage), and intestine. The annexed digestive glands consisted of the liver and the exocrine pancreas. At the beginning of the preflexion stage, teeth were developed in the OPC. There were mucous cells in the esophagus secreting different glycoconjugates from hatching. The enterocytes in the posterior intestine exhibited supranuclear vesicles associated with protein absorption. Mucous cells were observed in the posterior intestine in the preflexion stage and, in the anterior region, ending the flexion stage. Each type of glycoconjugates has a specific role. Acidic mucins lubricate and protect from mechanical damage, sialomucines protect from bacterial infections and neutral mucins regulate the acidity of mucus secretion, protect against abrasion and participate in the formation of the chyme, indicating a pregastric digestion. The liver was present since hatching with pancreatic tissue inside and increased in size acquiring the typical structure with hepatocyte cords, sinusoids, vacuoles, and hepatic duct. The hepatocytes vacuolization increased with larval development. The pancreas became extra-hepatic, with basophilic acinar cells and acidophilic zymogen granules. Throughout the ontogeny, the increased structural and functional complexity of the digestive system reflected the transition to exogenous feeding and nutritional increasing needs.     

Ontogeny of the digestive tract in sharpsnout sea bream Diplodus puntazzo (Cetti, 1777)

The ontogeny of the digestive tract was studied histologically and histochemically in sharpsnout sea bream Diplodus puntazzo from hatching (0 DAH, Days After Hatching) until day 57 (57 DAH). At hatching, the digestive tract appeared as a histologically undifferentiated straight tube lying dorsally to the yolk sac. When the mouth opened at 3 DAH, the digestive tract was differentiated into buccopharynx, oesophagus, incipient stomach and intestine. The pancreas, liver and gall bladder were also differentiated at this stage and both the bile and pancreatic duct had opened into the anterior intestine. Active feeding began in 50% of larvae at 4 DAH, although permanence of yolk reserves until 7 DAH suggests a period of both endogenous and exogenous feeding. Nutrient absorption was first visible from 5 DAH, as colourless supra- and infranuclear vacuoles in the anterior intestinal mucosa, suggesting a lipid content, as well as supranuclear, eosinophilic vacuoles, containing protein, in the posterior intestinal mucosa. Early caecal development could be detected from 10 DAH, whereas gastric glands appeared at 30 DAH, indicating the transition from larval to juvenile stage and the acquisition of an adult mode of digestion. Goblet cells appeared in the digestive tract of sharpsnout sea bream larvae shortly after first feeding. The mucus content of goblet cells varied with the digestive region and, in the buccal cavity and oesophagus, also with the developmental phase. This study provides knowledge for better husbandry practices in the aquaculture industry, as well as for the implementation of future nutritional studies.     

慈菇蛋白酶抑制剂对亚洲玉米螟消化酶的影响

亚洲玉米螟幼虫中肠消化酶主要为胰蛋白酶：利用慈菇蛋白酶抑制剂研究它对玉米螟消化酶的影响,发现这种抑制剂体外强烈抑制玉米螟幼虫中肠消化酶：同时我们又比较了长时间取食（三龄至五龄第二天）和短时间取食(四龄未取食48小时)抑制剂的幼虫体内胰蛋白酶活性,当它们短时间取食抑制剂后,体内消化酶水平迅速下降,取食更长时间时,胰蛋白酶活力下降更明显,仅为对照的27．2%。由此可见,慈菇蛋白酶抑制剂严重影响了玉米螟的正常消化,阻断了玉米螟营养与食物间的联系．使玉米螟生长发育不良。     

The ontogeny of the alimentary tract of larval pandora, Pagellus erythrinus L.

The ontogenesis of the alimentary tract and its associated structures (liver, pancreas, gall bladder) was studied in common pandora Pagellus eythrinus L., a promising species for diversification in Mediterranean aquaculture. Mass production of pandora has been limited so far by high larval and juvenile mortalities, which appear to be related to nutritional deficiencies. The development of the larval digestive system was studied histologically from hatching (0 DAH) until day 50 (50 DAH) in reared specimens, obtained by natural spawning from a broodstock adapted to captivity. At first feeding (3–4 DAH) both the mouth and anus had opened and the digestive tract was differentiated in four portions: buccopharynx, oesophagus, incipient stomach and intestine. The pancreas, liver and gall bladder were also differentiated at this stage. Soon after the commencement of exogenous feeding (5–6 DAH), the anterior intestinal epithelium showed large vacuoles indicating the capacity for absorption of lipids, whereas acidophilic supranuclear inclusions indicating protein absorption were observed in the posterior intestinal epithelium. Both the bile and main pancreatic ducts had opened in the anterior intestine, just after the pyloric sphincter, at this stage. Intestinal coiling was apparent since 4 DAH, while mucosal folding began at 10 DAH. Scattered mucous cells occurred in the oral cavity and the intestine, while they were largely diffused in the oesophagus. Gastric glands and pyloric caeca were firstly observed at 28 DAH and appeared well developed by 41 DAH, indicating the transition from larval to juvenile stage and the acquisition of an adult mode of digestion.     

幼虫密度对草地螟食物利用率及消化酶活性的影响

为了阐明草地螟Loxostege sticticalis大发生种群幼虫取食行为特征, 在室内条件下（温度22±1℃, 相对湿度70%）对不同幼虫密度［1, 10, 30头/瓶（650 mL）］饲养草地螟幼虫的食物利用率及消化酶活性进行了研究。结果表明： 幼虫中等（或高）密度对草地螟幼虫相对中肠重量、 相对取食量、 粪便干重、 食物利用率和近似消化率及总蛋白酶和亮氨酸氨肽酶活性影响显著。幼虫相对中肠重量以10头/瓶的幼虫密度最大, 1头/瓶的幼虫密度最小。随着幼虫密度的增加, 幼虫相对取食量和粪便干重增加, 而虫体干重减轻, 幼虫食物利用率降低。幼虫密度30头/瓶的幼虫相对取食量和粪便干重显著高于1和10头/瓶的, 而30头/瓶的幼虫食物利用率显著低于1头/瓶的。幼虫近似消化率随幼虫密度的逐渐增加而显著降低。幼虫密度10头/瓶的幼虫总蛋白酶和亮氨酸氨肽酶的活性显著高于1和30头/瓶的, 而淀粉酶的活性受幼虫密度影响不显著。随幼虫密度的增加, 幼虫相对中肠重量与总蛋白酶和亮氨酸氨肽酶活性变化趋势较为一致, 消化酶活性的变化可能与相对中肠重量大小有关。因此, 幼虫密度是影响草地螟幼虫取食行为的重要因子, 这些结果为阐明草地螟大发生种群与一般种群的为害特征提供了重要理论依据。     

A comparison of the molar efficiency of two insect-eating mammals

The extent to which the different molar morphologies of two similar-sized mammals, Petaurus breviceps (sugar glider) and Dasyuroides byrnei (kowari), could affect the digestion of larval insect nitrogen was investigated. Nitrogen digestibility of Tenebrio larvae treated with a proteolytic enzyme (trypsin) increased with decreasing larval piece size. However, it was found that the molars of P. breviceps , with their minimal shearing capacity compared with D. byrnei , can only compress rather than finely comminute Tenebrio larvae. As a result, P. breviceps have less efficient nitrogen digestibility than D. byrnei whose shearing molars can finely comminute larvae. Petaurus breviceps molars are inefficient at breaking down insects possibly because of functional constraints, where the molars must perform several different tasks with competing morphological demands, or because of phylogenetic constraints.     

Anti-nutritional effects of a moderate dose of soybean agglutinin in the rat

This study was conducted to investigate the effects of a moderate dose of purified soybean agglutinin on performance and nitrogen digestibility in rats as well as to determine its effects on the protein, DNA and RNA content of the small intestine and pancreas. Twenty-four Sprague - Dawley rats were randomly allotted into one of four groups for a 10-day nitrogen balance experiment. The four groups of rats were fed 7 g of a casein-cornstarch based diet or a similar diet supplemented with 0.1, 0.2 or 0.4 mg/g purified soybean agglutinin. All experimental diets were adjusted to an identical nutrient level. Dose of soybean agglutinin had no significant effect on rat performance. Incorporation of soybean agglutinin in the diet reduced apparent protein digestibility and the utilization of dietary protein by increasing nitrogen loss from the faeces and urine. Fresh pancreatic weight increased in rats fed soybean agglutinin at a level of 0.4 mg/g in the diet compared to the control, but the dry pancreatic weight and the protein content of the pancreas did not differ among the four groups. However the DNA and RNA content of the pancreas had a tendency to increase with a higher level of soybean agglutinin. The weight of the jejunum and its protein, DNA and RNA content were not significantly affected by soybean agglutinin, but the dry weight and the RNA of the jejunum tended to increase with higher levels of soybean agglutinin in the diet. In conclusion, purified soybean agglutinin, at moderate levels in the rats diet, had negative effects on digestive function, such as nitrogen digestibility, nitrogen retention and nitrogen balance. As the level of soybean agglutinin increased, the effects became more pronounced. Meanwhile, hypertrophy of the pancreas was observed with higher doses of soybean agglutinin incorporation in the diets.     

Absence of the major zymogen granule membrane protein, GP2, does not affect pancreatic morphology or secretion

The majority of digestive enzymes in humans are produced in the pancreas where they are stored in zymogen granules before secretion into the intestine. GP2 is the major membrane protein present in zymogen granules of the exocrine pancreas. Numerous studies have shown that GP2 binds digestive enzymes such as amylase, thereby supporting a role in protein sorting to the zymogen granule. Other studies have suggested that GP2 is important in the formation of zymogen granules. A knock-out mouse was generated for GP2 to study the impact of the protein on pancreatic function. GP2-deficient mice displayed no gross signs of nutrient malab-sorption such as weight loss, growth retardation, or diarrhea. Zymogen granules in the GP2 knock-out mice appeared normal on electron microscopy and contained the normal complement of proteins excluding GP2. Primary cultures of pancreatic acini appropriately responded to secretagogue stimulation with the secretion of digestive enzymes. The course of experimentally induced pancreatitis was also examined in the knock-out mice because proteins known to associate with GP2 have been found to possess a protective role. When GP2 knock-out mice were subjected to two different models of pancreatitis, no major differences were detected. In conclusion, GP2 is not essential for pancreatic exocrine secretion or zymogen granule formation. It is unlikely that GP2 serves a major intracellular role within the pancreatic acinar cell and may be functionally active after it is secreted from the pancreas.     

Potential role of cathepsin B in the embryonic and larval development of clam Meretrix meretrix

This study was designed to investigate the possible role of Meretrix meretrix cathepsin B (MmeCB) in embryonic and larval development. MmeCB mRNA expression profile was revealed by semi-quantitative RT-PCR. The level of MmeCB mRNA expression was low in trochophore stage but high in pedveliger stage. MmeCB protein expression was detected in the digestive gland, velum, and epidermis along the edges of the shell in D-larvae and pedveligers by immunocytochemistry. In post larvae, MmeCB protein expression was noticed abundant in the digestive gland, whereas a modest expression was identified in the gill filament. The average shell length of larvae hatched from embryos treated with 0.01, 1, and 10?μmol/L Ca074Me (a cathepsin B inhibitor) was significantly shorter than that of control groups. The metamorphosis rates of larvae treated with 0.01 and 1?μmol/L Ca074Me were significantly lower than that of control groups in 4-day larvae, but not in 5-day larvae. Taken together, these results indicated that MmeCB may have stimulatory effects on embryonic development, metamorphosis, and larval growth during M. meretrix larval development.     

Effects of rearing density on larval growth and activity of digestive enzymes in Lymantria dispar L. (Lepidoptera: Lymantriidae)

Density dependent responses of 4th, 5th and 6th instar gypsy moth larvae were studied at the level of larval mass, midgut loading and activities of three digestive enzymes (alpha-amylase, trypsin and leucine aminopeptidase). High density significantly reduced larval mass while midgut loading (expressed as relative midgut mass) did not change except in the 5th instar where it was increased at high density. Specific amylase and leucine aminopeptidase activities were not affected by crowding. Specific trypsin activity was on average higher in crowded than in isolated larvae. High density also affected the correlations between midgut protein content and activities of two proteolytic enzymes suggesting differences in regulatory mechanisms of insect digestion. The importance of these changes for survival under stressful conditions is discussed.     

Food and secretagogue stimulation decrease the digestive enzyme content remaining in the rat pancreas

The aim of the study reported here was to investigate changes in the digestive enzyme content in the pancreas after food and secretagogue stimulation. Rats from which food had been withheld overnight were either fed (between 6 and 8 a.m.) or not before euthanasia and pancreatic excision (at 8 a.m.: 21 not fed and 21 fed) and at 4 (12 p.m.: six not fed and six fed) and 8 h later (4 p.m.: six not fed and six fed). Another 16 rats were anesthetized, fitted with jugular vein and pancreatic duct catheters, and infused with the secretagogues, CCK-33 and secretin, during 1.5 h of pancreatic juice collection before euthanasia and pancreatic excision. The pancreata were homogenized, and total soluble protein and individual enzyme (trypsin and amylase) tissue contents were analyzed. Results indicated lower amounts of protein and enzymes remaining in the pancreata of the fed, compared with non-fed rats. Enzyme values indicated recovery within four hours in fed rats, but non-fed rats also had increased values during daytime. High enzyme secretion during the high dose of hormonal stimulation was reflected in lower enzyme values remaining in the pancreas, compared with that in response to low-dose stimulation. Results indicated that stimulation of the pancreas, either by food ingestion or exogenous secretagogues, lowers the amounts of digestive enzymes remaining in the pancreas, and imply that stimulation and circadian rhythms influence the pancreatic enzyme content at euthanasia. This finding should be borne in mind in interpretation of data from pancreatic studies.     

猪对两种黑麦原料消化性的研究

分别以HH91和Pluto两种黑麦作为饲料来源进行消化试验.结果 表明,喂饲HH91黑麦组日粮中干物质、粗蛋白、粗纤维、无氮浸出物、有机物等的表观消化率、总能的表观消化率、日粮可消化蛋白质的利用系数和N平衡等均高于Pluto组,其中粗纤维的表观消化率有极显著性的差异( P<0.01),有机物表观消化率差异性显著(P<0.05),其余指标差异不明显(P >0.05).喂饲HH91黑麦组日粮中粗脂肪、粗灰分和总能的表观消化率则低于Pluto组,但差异不明显( P >0.05).     

西江鲤仔稚鱼生长及消化酶活性变化

为了探究了鲤(Cyprinus carpio)仔稚鱼的生长过程中主要消化酶活性变化规律, 实验测定了鲤从孵化出膜到40 日龄(日龄, Day after hatching)仔稚鱼期间的生长、可溶性蛋白含量和几种消化酶活性变化。结果显示: 仔稚鱼全长以及体重在15 日龄后增速加快, 特定生长率为14.81%。淀粉酶、脂肪酶、胰蛋白酶, 糜乳蛋白酶、碱性磷酸酶以及氨基肽酶在1 日龄仔鱼体内均能检测到活性。在仔稚鱼发育过程中, 其可溶性蛋白含量先下降后上升。仔鱼摄食前消化酶的活性出现一定的上升, 随着仔稚鱼消化系统发育以及营养方式的转变, 其消化酶活性从3到25 日龄处于不断的变化状态, 而25 日龄到实验结束鲤仔稚鱼的消化酶处于一种相对稳定的状态, 标志着其消化功能趋于完善。根据不同发育时期鲤消化酶活性的变化, 设计有机可腐化的材料制备人工鱼巢以提高人工鱼巢的生态修复功能, 降低饥饿对仔稚鱼成活率的影响。     

梨小食心虫幼虫中肠中高表达消化酶和解毒酶基因的筛选

【目的】挖掘梨小食心虫Grapholita molesta幼虫中肠中高表达消化酶和解毒酶基因,为今后研究以肠道为靶标的新型农药和转基因作物提供理论依据。【方法】基于梨小食心虫4龄幼虫中肠转录组高通量测序数据的FPKM值,筛选高表达基因,进行GO功能注释和KEGG通路富集分析,并使用BLAST软件进行比对筛选高表达的消化酶和解毒酶基因,利用MEGA对这些高表达的消化酶和解毒酶及其他鳞翅目昆虫的同源蛋白进行系统发育分析。利用qRT-PCR技术对梨小食心虫幼虫不同龄期中肠中的高表达代表性消化酶和解毒酶基因表达量进行定量分析和验证。【结果】在GO数据库中注释了103 677个在梨小食心虫4龄幼虫中肠中高表达基因,包括细胞组分、分子功能和生物学进程三大类功能共41个分支。KEGG通路分析表明,10 846个高表达基因参与了5类生化代谢通路。筛选到具有完整开放阅读框的消化酶基因17个[5个胰蛋白酶(trypsin, TRY)基因、3个氨肽酶(aminopeptidase, APN)基因和9个羧肽酶(carboxypeptidase, CP)基因]和解毒酶基因32个[11个谷胱甘肽S-转移酶(glu...