Ontogeny of the digestive tract in stinging catfish, Heteropneustes fossilis (Bloch) larvae.

Heteropneustes fossilis (Bloch) is an important candidate species for diversification of freshwater aquaculture in India. However, high mortality rate during larval rearing is the most serious bottleneck in commercial production of this species. A proper understanding of the ontogenic development of digestive system provides the basis to understand the nutritional physiology of larvae and develop appropriate feeding strategies. In the present study, the ontogenical development of the digestive tract in H. fossilis larvae was studied from hatching until 30 day post-hatching (dph) at 29 °C. At hatching (2.8 ± 0.2 mm standard length, SL), the digestive tract was undifferentiated and attached dorsally to the yolk sac. At 1 dph (2.9 ± 0.2 mm SL), the mouth opened and oral valves were visible. At 2 dph (3.0 ± 0.3 mm SL), goblet cells were observed in the buccoparyngaeal cavity. At this age, exogenous feeding started and the intestine was differentiated into the anterior and posterior regions, and the rudimentary liver and pancreas were also seen. Small supranuclear vacuoles were observed in the enterocytes of the posterior intestine at 2 dph. Zymogen granules were observed in acinar cells of pancreas by 3 dph, and islets of Langerhans were visible at 4 dph (3.5 ± 0.1 mm SL). At the same age, most of the yolk sac reserves were consumed, whereas they were completely exhausted by 5 dph (3.9 ± 0.5 mm SL). Between 4 and 6 dph, the liver elongated in size and started to accumulate lipids in the hepatocytes. Gastric glands were detected at 4 dph, and the pyloric sphincter was completely differentiated at 9 dph (6.1 ± 0.4 mm SL) as an epithelial fold that separated stomach from the anterior intestine. By 13 dph (8.6 ± 0.2 mm SL), profuse gastric glands were visible inside longitudinal mucosal folds of the stomach. The formation of gastric glands and their development were noticed as the last events in the development of the digestive tract in H. fossilis. This indicated the end of the larval period and the commencement of the juvenile stage. Considering these observations, it is suggested that H. fossilis larvae have a morphologically complete digestive tract by 13 dph. The findings of the study on the development of the digestive system in H. fossilis may help in synchronising the larval stage of development and feeding strategies and would be helpful in improving larval rearing techniques for catfish species.

Histological study of the gastrointestinal tract in longfin yellowtail (Seriola rivoliana) larvae.

This work contributes basic knowledge on larval development of Seriola rivoliana. A histological study describes the development of the digestive tract and accessory glands in S. rivoliana larvae reared under laboratory conditions at 24 °C from hatching to 30 days post-hatching (DPH). At hatching (2.6 ± 0.12 mm), larvae had an undifferentiated digestive tract with a closed straight tube and a large yolk sac with an oil globule. The liver and pancreas were observed at 1 and 2 days, and the mouth and anus opened at day 2. Enriched rotifers were visible in their digestive tract. At the beginning of the pre-flexion stage, a mixed nutritional period was observed. At day 3, exogenous feeding began; the digestive tract became differentiated into the buccopharynx, esophagus, an undifferentiated stomach, and the intestines. Zymogen granules were visible in the exocrine pancreas. At day 4, supranuclear vacuoles were present in the posterior intestine, indicating the beginning of intracellular digestion. At day 5, goblet cells were present in the esophagus and became functional at day 7 in the esophagus and intestine. The buccopharynx goblet cells developed at day 15. The presence of gastric glands and differentiation of the stomach in the fundic, cardiac, and pyloric regions during the post-flexion stage occurred at day 20. This was the onset of the juvenile period and the beginning of weaning; however, a long co-feeding phase is recommended. Pyloric caeca were observed at day 30 (13.6 ± 1.6 mm). These results provide valuable information on S. rivoliana larvae biology and digestive physiology, which should be useful to improve cultivation techniques and identify ecological features involved in ontogeny.

Morphological and histological changes in digestive tract development during starvation in the miiuy croaker.

A histological method was used to describe the ontogenetic development of the digestive tract of laboratory-reared miiuy croaker (Miichthys miiuy) and to evaluate the effects of short-term food deprivation on the morphology and histology of the digestive tract. Larvae and juveniles were maintained at 24 °C in a thermostatically controlled system. Three starvation experiments were conducted during different developmental stages: 1-7 days after hatching (dah; prior to benthic swimming); 26-35 dah (during settling); and 42-53 dah (after benthic swimming). According to the structural changes in the ontogenetic development of the digestive tract, three stages were observed. The first stage was from hatching to 3 dah; the digestive tract was undifferentiated in newly hatched larvae and then showed remarkable morphological changes and differentiation. During this period, larvae depended on endogenous nutrition. The second stage (4-20 dah) was a critical period in which larvae transitioned from endogenous feeding to exogenous feeding and the digestive tract fully differentiated into the buccopharynx, oesophagus, stomach, anterior intestine and posterior intestine. Goblet cells and vacuoles appeared in the digestive tract, and pharyngeal teeth and taste buds developed. During the third stage (20-36 dah), the gastric glands developed and the stomach differentiated into the fundic, cardiac and pyloric regions. At 25 dah, pyloric caeca developed and mucosal folds and spiral valves were clearly distinguishable. After 30 dah, the digestive tract did not undergo any noticeable differentiation, indicating the complete development of the digestive system. The wet weight and SGR (specific growth rate) of miiuy croaker larvae and juveniles greatly decreased when they were deprived of food, and compensatory growth was observed in re-feeding juveniles. The livers of starved larvae and juveniles were atrophied and dark coloured, the intestines were transparent and thin, and the stomach cubages were reduced. The histological effects of starvation were mainly evident in the degeneration of cells in digestive organs, as seen in the shrinkage and separation of cells and the loss of intercellular substances in the liver, pancreas, intestine and stomach. These changes became more severe with increased duration of starvation. In addition, the histological structure of the digestive tracts of starved larvae and juveniles partly recovered after re-feeding, and the effects of starvation on miiuy croaker were age dependent.

Ontogeny of the digestive tract of Centropomus parallelus larvae.

Development of the digestive tract and accessory glands of larvae of the fat snook Centropomus parallelus was examined under light microscopy, from hatching to 60 day post-hatching (dph). At hatching, the digestive tract is straight and composed by a cubic cell layer. The exogenous feeding starts at 3 dph, concomitantly with the mouth opening and subdivision of the rudimentary stomach and esophagus. At 4 dph, the intestine has three sectins, and vacuoles are observed in the posterior section, indicating the beginning of protein digestion and absorption. The pharyngeal teeth appear at 9 dph, and goblet cells appear at 13 dph in the esophagus. Gastric glands appear at 30 dph, marking the beginning of weaning. The disappearance of supranuclear vacuoles in the posterior intestine occurs at 35 dph, suggesting efficiency of extracellular digestion. This study shows that C. parallelus larvae is able to start weaning 15 days earlier than reported in earlier studies, increasing the success of larviculture.

Digestive system development and study of acid and alkaline protease digestive capacities using biochemical and molecular approaches in totoaba (Totoaba macdonaldi) larvae.

The present study aimed to describe and understand the development of the digestive system in totoaba (Totoaba macdonaldi) larvae from hatching to 40 days post-hatch (dph) from morphological and functional perspectives. At hatch, the digestive system of totoaba was undifferentiated. The anus and the mouth opened at 4 and 5 dph, respectively. During exogenous feeding, development of the esophagus, pancreas, liver and intestine was observed with a complete differentiation of all digestive organs. Expression and activity of trypsin and chymotrypsin were observed as early as at 1 dph, and increments in their expression and activity coincided with changes in food items (live and compound diets) and morpho-physiological development of the accessory digestive glands. In contrast, pepsin was detected later during development, which includes the appearance of the gastric glands between 24 and 28 dph. One peak in gene expression was detected at 16 dph, few days before the initial development of the stomach at 20 dph. A second peak of pepsin expression was detected at day 35, followed by a peak of activity at day 40, coinciding with the change from live to artificial food. Totoaba larvae showed a fully morphologically developed digestive system between 24 and 28 dph, as demonstrated by histological observations. However, gene expression and activity of alkaline and acid proteases were detected earlier, indicating the functionality of the exocrine pancreas and stomach before the complete morphological development of the digestive organs. These results showed that integrative studies are needed to fully understand the development of the digestive system from a morphological and functional point of views, since the histological organization of digestive structures does not reflect their real functionality. These results indicate that the digestive system of totoaba develops rapidly during the first days post-hatch, especially for alkaline proteases, and the stomach becomes functional between 20 and 24 dph allowing the weaning process to begin at this age.

Effect of novel fiber ingredients on ileal and total tract digestibility of energy and nutrients in semi-purified diets fed to growing pigs.

BACKGROUND: Consumption of different dietary fibers may influence the digestibility of carbohydrates and other nutrients. Therefore the objectives of this experiment were to determine the effect of novel fiber ingredients on the apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of gross energy (GE), dry matter (DM), crude protein (CP) and total dietary fiber (TDF) in pigs and to calculate the standardized digestibility of analyzed TDF in four novel fiber ingredients. RESULTS: The AID of DM and GE in diets containing novel fiber ingredients was less (P < 0.05) than in a maltodextrin diet. Addition of cellulose or pullulan, but not resistant starch (RS) 60, RS 75 or soluble corn fiber 70, reduced (P < 0.05) the AID of CP. The average ileal and total tract endogenous losses of analyzed TDF were calculated at 25.25 and 42.87 g kg⁻¹ DM intake, respectively. CONCLUSION: Addition of novel fiber ingredients to a maltodextrin-based diet had different effects on the AID of DM, CP, GE and TDF. Measurements of the standardized digestibility of analyzed TDF may be a better indicator of TDF fermentability than measurements of AID and ATTD of TDF, because some endogenous metabolites may be analyzed as TDF.

Gut-associated bacteria throughout the life cycle of the bark beetle Dendroctonus rhizophagus Thomas and Bright (Curculionidae: Scolytinae) and their cellulolytic activities.

Dendroctonus rhizophagus Thomas and Bright (Curculionidae: Scolytinae) is an endemic economically important insect of the Sierra Madre Occidental in Mexico. This bark beetle has an atypical behavior within the genus because just one beetle couple colonizes and kills seedlings and young trees of 11 pine species. In this work, the bacteria associated with the Dendroctonus rhizophagus gut were analyzed by culture-dependent and culture-independent methods. Analysis of 16S rRNA sequences amplified directly from isolates of gut bacteria suggests that the bacterial community associated with Dendroctonus rhizophagus, like that of other Dendroctonus spp. and Ips pini, is limited in number. Nine bacterial genera of γ-Proteobacteria and Actinobacteria classes were detected in the gut of Dendroctonus rhizophagus. Stenotrophomonas and Rahnella genera were the most frequently found bacteria from Dendroctonus rhizophagus gut throughout their life cycle. Stenotrophomonas maltophilia, Ponticoccus gilvus, and Kocuria marina showed cellulolytic activity in vitro. Stenotrophomonas maltophilia, Rahnella aquatilis, Raoultella terrigena, Ponticoccus gilvus, and Kocuria marina associated with larvae or adults of Dendroctonus rhizophagus could be implicated in nitrogen fixation and cellulose breakdown, important roles associated to insect development and fitness, especially under the particularly difficult life conditions of this beetle.

Ontogeny of the digestive tract in butter catfish Ompok bimaculatus (Bloch) larvae.

The ontogeny of the digestive tract was studied histologically in butter catfish Ompok bimaculatus from hatching to 30 days post-hatching (dph). At hatching, the digestive tract of butter catfish consisted of a straight tube with a smooth lumen dorsally attached to the yolk sac. Between 1 and 2 dph, the mouth opened, oral valves were visible and canine-like teeth and taste buds were detected. During this period, intestine was differentiated into the anterior and posterior intestine, and the digestive accessory glands were also developed. Exogenous feeding started at 2 dph, and there was a 2-day mixed endogenous-exogenous feeding period. Most of the yolk sac reserves were consumed between 2 and 3 dph, and by 5 dph, the yolk sac was completely depleted and no longer visible in histological sections. Between 3 and 4 dph, several vacuoles (neutral lipids) were observed in the intestine and also in hepatocytes, indicating a functional absorption of nutrients from food. At 8 dph, differentiation of gastric glands was noticed, and by 9-11 dph, there were abundant gastric tubular glands arranged along numerous longitudinal folds. During the same period, pyloric sphincter appeared as an epithelial fold that separated the stomach from the anterior intestine. From 12 dph to the end of the study at 30 dph, no noticeable histological modifications were observed. The development of gastric glands is considered as the last major events in digestive tract development and their presence designates the end of larval period and the onset of the juvenile period. Hence, it is suggested that, butter catfish larvae have a morphologically complete digestive tract by 12 dph. These findings on the development of the digestive system in butter catfish may lead to a better understanding of the ontogeny and would be useful to improve the larval rearing techniques of this promising catfish species for freshwater aquaculture diversification.

Ontogeny of the digestive tract and enzymes in rock bream Oplegnathus fasciatus (Temminck et Schlegel 1844) larvae.

Histological development of the digestive tract and specific activities of three digestive enzymes (trypsin, alkaline phosphatase, and pepsin) were studied in rock bream Oplegnathus fasciatus from hatching to 50 days after hatching (DAH). At hatching, the digestive tract appeared as an undifferentiated straight tube and differentiated into the buccopharynx, esophagus, stomach, intestine, and rectum at mouth opening by 3 DAH. The taste bud and mandibular teeth were present in the buccopharyx at 8 DAH. The goblet cells appeared in the esophagus at 8 DAH and in the buccopharyx at 9 DAH. The stomach anlage was formed at 2 DAH and developed into cardia, fundus, and pylorus at 14 DAH. The gastric glands were visible at 16 DAH, and the pepsin was firstly detected on 22 DAH. At 2 DAH, the intestinal valve appeared and divided the intestine into anterior intestine (AI) and posterior intestine (PI). The rectum was differentiated from the PI at 3 DAH. The supranuclear vacuoles were visible in the rectum by 6 DAH, and the lipid inclusions were present in the AI at 8 DAH. The alkaline phosphatase was detected at 1 DAH, and the increase in its activity indicated the maturation of the intestine after 40 DAH. The hepatocytes and pancreatic cells were differentiated from the blast cells at 2 DAH, and the acidophilic zymogen granules in the exocrine pancreas were observed simultaneously. The trypsin was detected by 1 DAH and increased to the maximum at 19 DAH, followed by a decrease as the stomach became functional.

Kiwifruit (Actinidia deliciosa), compared with cellulose and psyllium, influences the histology and mucus layer of the gastrointestinal tract in the growing pig.

Kiwifruit (KF) fiber, a mixture of soluble and insoluble fibers, elicits mucosal changes in the gastrointestinal tract (GIT). This study aimed to define the nature of these changes in mucosal features throughout the GIT of the growing pig in response to semi-synthetic iso-fiber diets containing cellulose (CEL, low GIT luminal functionality) as the sole fiber source (4.5%), or diets where half of the CEL was replaced by either PSY fiber (PSY husk, high GIT luminal functionality) or KF fiber (consumed as intact fruit). Entire male growing pigs (n = 24, 21 kg bodyweight) received the three diets (n = 8) for 42 d. GIT tissues, digesta, and feces were sampled. The partial replacement of CEL increased (P≤ 0.05) the ileal (KF 22% and PSY 33%) and colonic (PSY 86%) mucus layer thickness, whereas it decreased the rectal crypt depth (KF -26%), and small intestinal (duodenum to ileum) villus length (PSY -17%). The number of duodenal goblet cells was 77% higher (P≤ 0.05) for KF than CEL. Pigs fed the KF-containing diet had greater (P≤ 0.05) apparent ileal organic matter digestibility and apparent total tract organic matter digestibility compared with CEL, but the lowest amount of fermented organic matter in the large intestine. In conclusion, partial substitution of CEL with PSY or KF at a constant, practically-relevant dietary fiber intake, affected several measures of GIT functionality with effects being specific to the added fiber.

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.

Early development of the digestive tract (pharynx and gut) in the embryos and pre-larvae of the European sea bass Dicentrarchus labrax.

The European sea bass Dicentrarchus labrax is a marine teleost important in Mediterranean aquaculture. The development of the entire digestive tract of D. labrax, including the pharynx, was investigated from early embryonic development to day 5 post hatching (dph), when the mouth opens. The digestive tract is initialized at stage 12 somites independently from two distinct infoldings of the endodermal sheet. In the pharyngeal region, the anterior infolding forms the pharynx and the first gill slits at stage 25 somites. The other three gill arches and slits are formed between 1 and 5 dph. Posteriorly, in the gut tube region, a posterior infolding forms the foregut, midgut and hindgut. The anus opens before hatching, at stage 28 somites. Associated organs (liver, pancreas and gall bladder) are all discernable from 3 dph. Some aspects of the development of the two independent initial infoldings seem original compared with data in the literature. These results are discussed and compared with embryonic and post-embryonic development patterns in other teleosts.

Ontogenic development of the digestive tract in larval and juvenile Vimba bream, Vimba vimba.

In this study we examined the ontogenic development of the digestive tract of Vimba bream (Vimba vimba, Family: Cyprinidae) during the first 60 days of life (hatching to 60 days after hatching [DAH]). Samples of developing Vimba bream were randomly selected at various stages of development: 1-8, 10, 15, 20, 25, 30, 40, 50, and 60 DAH. For the histological and histochemical studies on the development of the alimentary canal, tissue sections prepared from the sampled hatchlings were stained with hematoxylin-eosin and periodic acid-Schiff and observed under a light microscope. The histological structures of both the mouth and esophagus were fully developed at 5 and 7 DAH, respectively. Intestinal differentiation was observed at 2 DAH, while mucosal folds appeared on the intestinal bulb at 7 DAH. At 5 DAH, with the appearance of goblet cells in the epithelium of the mouth, pharynx, and esophagus, the larvae showed secretion activity in these organs. At 6 DAH, secretion was observed in the intestine; at this stage of development, the surface of the gastrointestinal tract was covered in a neutral mucous-like layer of polysaccharide. The histological observations indicate that the early development of the digestive tract in Vimba vimba enables larvae to efficiently ingest and digest exogenous feed very quickly after hatching.

Foregut morphology and ontogeny of the mud crab Dyspanopeus sayi (Smith, 1869) (Decapoda, Brachyura, Panopeidae).

The morphology of the foregut of the Say's mud crab Dyspanopeus sayi was described in adults and larvae. The ossicle system was illustrated based on a staining method with Alizarin-Red. The gastric teeth and cardio-pyloric valve were dissected and examined using optical and scanning electron microscopy. In the adults, the morphology of ossicles and gastric teeth of D. sayi is very similar to the related species Rhithropanopeus harrisii. The foregut of first zoea (ZI) presented a functional cardio-pyloric valve while the filter press was lacking. The filter press was observed in the pyloric chamber from ZII. The most significant changes in morphology take place after metamorphosis from ZIV to megalopa, including the occurrence of the gastric mill. The organization and morphology of many megalopal foregut ossicles are recognizable in the adult phase, although the morphology of the gastric teeth differs from the morphology of adults. A correlation of gastric mill structures with food preferences and their contribution to the phylogeny are briefly discussed.

Expression and activity of trypsin and pepsin during larval development of the spotted rose snapper Lutjanus guttatus.

The present study aimed to describe and understand the development of the digestive system in spotted rose snapper (Lutjanus guttatus) larvae from hatching to 40 days post-hatch (dph). The mouth opened between 2 and 3 dph, at that moment the digestive tract was barely differentiated into the anterior and posterior intestine, although the liver and pancreas were already present. Gastric glands were observed until 20 dph, followed by the differentiation of the stomach between 20 and 25 dph. Trypsinogen expression and trypsin activity were detected at hatching, increasing concomitantly to larval development and the change in the type of food. Maximum levels of trypsinogen expression were observed at 25 dph, when animals were fed with Artemia nauplii, and maximum trypsin activity was detected at 35 dph, when larvae were fed with an artificial diet. On the other hand, pepsinogen gene expression was detected at 18 dph, two days before pepsin enzymatic activity and appearance of gastric glands. Maximum pepsin activity was also observed at 35 dph. These results suggest that in this species weaning could be initiated at an earlier age than is currently practiced (between 28 and 30 dph), since larvae of spotted rose snapper develop a functional stomach between days 20 and 25 post-hatch.

Metamorphic remodeling of a planktotrophic larva to produce the predatory feeding system of a cone snail (Mollusca, Neogastropoda).

I used histological sections and 3D reconstructions to document development through metamorphosis of the foregut and proboscis in the conoidean neogastropod Conus lividus. A goal was to determine how highly derived features of the post-metamorphic feeding system of this gastropod predator develop without interfering with larval structures for microherbivory. A second goal was to compare foregut development in this conoidean with previous observations on foregut development in the buccinoidean neogastropod Nassarius mendicus. These two neogastropods both have a feeding larval stage, but they show major differences in post-metamorphic foregut morphology. Basic events in development of the proboscis and proboscis sheath in C. lividus and N. mendicus were similar. However, the elongate buccal tube of C. lividus forms during metamorphosis as a composite of apical epidermal tissue that grows inward and ventral foregut tissue that extends outward. The larval mouth is not carried through metamorphosis. Comparative observations on foregut development in caenogastropods, which now include data on C. lividus, suggest that the foregut incorporates dorsal and ventral modules having different ontogenetic and functional fates. This developmental modularity may have facilitated evolutionary diversification of the post-metamorphic foregut. Foregut diversification in predatory gastropods may have been further fast-tracked by developmental uncoupling of larval and post-metamorphic mouths.