Pyloric Ceca Research Articles

Anionic Trypsin from the Pyloric Ceca of Pacific Saury (Cololabis saira): Purification and Biochemical Characteristics

Anionic trypsin from Pacific saury (Cololabis saira) pyloric ceca was purified to homogeneity by ammonium sulfate precipitation, ion-exchange chromatography, and gel filtration chromatography. It was purified to 53.7-fold with a yield of 6.1%. The apparent molecular weight of the enzyme was about 24 kDa, as determined by size exclusion chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). On native-PAGE, trypsin showed a single band. The purified anionic trypsin displayed optimal activity at pH 8.5 and 55°C. The enzyme was stable at neutral and alkaline pH and in the temperature range of 20–50°C. The stability was affected by the calcium ion. The activity of purified anionic trypsin was completely inhibited by soybean trypsin inhibitor and N-p-tosyl-L-lysine chloromethyl ketone (TLCK) and partially inhibited by ethylenediaminetetraacetic acid (EDTA). NaCl (0–30%) decreased the activity in a concentration-dependent manner. The kinetic trypsin constants Km and Kcat were 0.19 mM and 210 s−1, respectively, while the catalytic efficiency (Kcat/Km) was 1105.26 s−1 mM−1. The N-terminal amino acid sequences of anionic trypsin, IVGGYECQAH, were found and were homologous to those of trypsin from other fish species.

Testing Protein Digestibility in Red Grouper Epinephelus Morio using In Vitro and In Vivo Methods

The digestibility of pre-selected ingredients was evaluated for Epinephelus morio using pH-stat and multi-enzyme extract (stomach, intestine, and ceca). The degree of hydrolysis (DH) was tested with acid and alkaline proteases using crustacean meals, squid meal, fish protein concentrate (FPC), fish meal, dried whey, as well as canola paste (w/ or w/o phytase), soybean meal (w/ or w/o phytase), soyprotein concentrate (SPC), and wheat gluten. SPC produced DH values between 3.6-4.1%, obtained from the three different parts of the digestive tract. Canola paste produced high DH in the stomach by adding phytase to 0.8 and 2% feed. This process was repeated under alkaline conditions for DH, with 0.6-2.6% in the pyloric ceca, and 1-2.2% in the intestine. The DH from stomach with crustacean meals (shrimp meal and crab meal) ranged from 32-87%, while values for dried whey from the ceca and intestine ranged from 6-7.4%. It did not differ from crab meal with values of 4.5 and 8.7% from pyloric ceca and intestine respectively. Based on the above results, 4 diets were developed using shrimp meal, dried whey, soy protein concentrate, and canola+phytase. The DH, FAA (fish amino acid) and SDS-PAGE (analysis of protein gels) for each diet were analysed. After an in vivo test, results on juveniles fed whey protein diet (WPd) and CPd+ ranked high (95% and 92% respectively) compared with other treatments. pH-Stat provided consistent results regarding digestibility of selected protein sources. Therefore, dried whey, shrimp meal, and canola+phytase ranked first to be included in E.morio feed formulation with a pool of 55% of these components, complemented with a minimum of fish meal, FPC, grains and wheat gluten

A new reliable reference gene UBA52 for quantitative real-time polymerase chain reaction studies in pyloric cecal tissues of the starfish Asterias rubens.

The starfish Asterias rubens is one of the most abundant echinoderm species in the White, Barents, North, and Baltic Seas. This species is an important component of marine ecosystems and a model object for certain biological studies, in particular those requiring quantitative estimation of gene expression. As a rule, expression at the transcriptional level is estimated by real-time qPCR using the ΔΔCt method, which allows the comparison of the copy number of target gene transcripts in samples with unknown mRNA/cDNA concentration. Application of this method requires normalization of the results relative to genes with stable expression levels (reference genes). The identification of reference genes is still a challenging task since data of this kind are missing for certain taxa, whereas the use of "standard" endogenous control genes without additional tests might lead to erroneous conclusions. We performed a preliminary analysis of the expression of many housekeeping genes in the pyloric ceca of A. rubens by high-throughput sequencing under normal and heat shock conditions. For one of them, the ubiquitin gene UBA52, low variation of expression (not greater than 2-fold) was shown using real-time qPCR. Tissues of pyloric ceca of normal adults and underyearlings and of adults after heat shock were used. The data obtained suggest that the UBA52 gene may be used as reference for normalization of gene expression at the mRNA level in the starfish A. rubens and probably in closely related species.

A novel, non-invasive and in vivo approach to determine morphometric data in starfish

Starfish (Echinodermata: Asteroidea) are present in most benthic ocean habitats and play an important ecological role as keystone species or by dominating through sheer individual numbers. In order to assess nutritional and reproductive states in ecological studies on asteroids, invasive techniques to calculate organ indices are conventionally used. We present a non-invasive method that enables imaging and morphometric measurements in starfish in vivo. We used a clinical 1.5T magnetic resonance imaging (MRI) scanner to produce sectional images of three starfish species and employed these image stacks to generate 3D models of the pyloric ceca, gonads and the endoskeleton. In comparison to pre-clinical MRI scanners, that provide higher resolutions, clinical MRI is not limited to small objects, but allows the investigation of larger samples such as the starfish used in the present study. Volume data from MRI-based 3D reconstructions were compared to conventional invasive measurement techniques as well as high resolution MRI scans and were tested for inter-observer effects. Here we show that MRI is a suitable method for precise imaging and volumetric measurements in fixed and living marine specimens. Compared to other methods, it allows not only the production of time series data on single individuals as well as populations, but also non-destructive analyses of valuable specimens, such as museum material.

Comparative infectivity of three larval nematode species in three different salmonids

Host specificity of parasites may depend both on ecological and physiological factors. Basic descriptions of the susceptibility/resistance of fish to specific nematodes are needed in order to reveal mechanisms in the host-parasite relation. Rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), and Atlantic salmon (Salmo salar) were orally infected with larval stages of three different anisakid nematodes-Hysterothylacium aduncum, Contracaecum osculatum, and Anisakis simplex-and parasite survival and location was subsequently recorded for up to 14 days post infection (dpi). H. aduncum was most prevalent and numerous in brown trout 2 dpi, but a large proportion of the worms were recovered dead. No tissue penetration was observed. Rainbow trout exhibited the highest susceptibility to C. osculatum larvae at 2, 7, and 14 dpi. Mean intensities and mean abundances were lower in brown trout and salmon at all time points. The pyloric cecum was penetrated in rainbow trout on two occasions. A. simplex larvae established more successfully in salmon compared to rainbow trout; brown trout exhibited the highest natural resistance. Mean intensity and mean abundance was highest in rainbow trout at 2 and 7 dpi, but not after 14 days. A range of tissues, including muscle and liver, were found penetrated by larvae, but the pyloric ceca were the preferred microhabitat for Anisakis in both rainbow trout and salmon. It can be concluded that closely related salmonids differ in susceptibility towards different anisakid larvae and these parasites select different microhabitats in the hosts. The physiological basis for this specificity is discussed.

Involvement of dietary salt in shaping bacterial communities in European sea bass (Dicentrarchus labrax)

Bacteria associated with the digestive tract of multicellular organisms have been shown to play a major role in their hosts' functioning. In fish, it has been proposed that food fermentation occurs inside the pyloric ceca, pouch like organs found in their digestive tract. However, this notion remains controversial. Furthermore, changes in pyloric cecal bacterial populations under different diets have yet to be demonstrated in fish. In this study, we explore the changes occurring in the bacterial community residing in the pyloric ceca of carnivorous fish fed different diets, which were shown to induce different growth rates. Our results revealed that different diets do indeed induce distinct bacterial compositions within the pyloric ceca. We found that, when salt was added to a low fish meal diet, the bacterial changes were accompanied by a significant enhancement in weight gain, hinting at a possible involvement of the bacterial community in energy harvest.

Ontogenetic Development of the Digestive Tract in Larvae of American Shad

AbstractThe American Shad Alosa sapidissima was introduced into China for aquaculture in 2003. The histological characteristics of the digestive tract of American Shad larvae were examined from hatching to 33 d after hatching (DAH) with the aim of cultivating the larvae efficiently. The fertilized American Shad eggs were imported from Oregon and incubated in barrels with spring water maintained at 20.3–21.9°C in Qingyuan, Guangdong Province, China. The larvae were transferred to cement pools (water temperature at 24.0–25.0°C) at 13 DAH. Larvae were fed Artemia nauplii starting at 3 DAH, Artemia nauplii supplemented with gradually increasing proportions of commercial formulated feed after 18 DAH, and then only the formulated feed by 30 DAH. Based on the source of nutrition and structural changes in the digestive tract, larval development was divided into three stages: (1) lecitotrophic (0–2 DAH), (2) lecitoexotrophic (3 DAH), and (3) exotrophic (4–33 DAH). At 0 DAH of the lecitotrophic stage, the digestive system was undifferentiated and contained a large acidophilic yolk sac. By 1 DAH, the mouth and anus opened, the liver appeared, and the buccopharynx and intestine began to differentiate. The lecitoexotrophic stage began at the start of exogenous feeding, which led to the disappearance of the yolk sac. During the exotrophic stage, the esophagus could be differentiated into two different regions by 4 DAH. The intestinal tract developed quickly and differentiated into an obvious foregut and hindgut by 11 DAH. The primary stomach formed by 8 DAH and completely developed by 19 DAH with the presence of a few gastric glands. By 25 DAH, many gastric glands and a number of pyloric ceca were observed. The results of the study show the quick development of the digestive system in American Shad and we suggest initiating the weaning process at 23–25 DAH in the larvae.

Characterization of cholecystokinin-producing cells and mucus-secreting goblet cells in the blacktip grouper, Epinephelus fasciatus

The characteristics and distributions of cholecystokinin (CCK)-producing cells and mucus-secreting goblet cells were investigated in the digestive tract of the blacktip grouper (Epinephelus fasciatus). CCK-producing cells were scattered throughout the digestive tract. The highest frequency of CCK-producing cells was observed in the anterior intestine portion and pyloric ceca, with a very small number of cells distributed as far as the rectum. Mucus-secreting goblet cells were found to differ remarkably in their regional distributions and relative frequencies. High frequencies of mucus-secreting goblet cells were found in the digestive tract, mainly in the anterior intestine portion and pyloric ceca, but not the esophagus; the frequency decreased slightly toward the rectum. Our result suggests that food digested by gastric acid in the stomach moves on the anterior (including the pyloric ceca) and mid intestine portion, thereby ensuring effective stimulation of the CCK-producing cells. In addition, the distribution pattern of the CCK-producing cells closely resembled that of mucus-secreting goblet cells. In E. fasciatus, CCK-producing cells and mucus-secreting goblet cells seem to be well adapted to promoting optimal control of the digestive process.

Selection for high muscle fat in rainbow trout induces potentially higher chylomicron synthesis and PUFA biosynthesis in the intestine

Two lines of rainbow trout divergently selected for muscle fat content, fat line (F) and lean line (L) were used to investigate the effect of genetic selection on digestion, intestinal nutrient transport and fatty acid bioconversion, in relation to dietary starch intake. This study involved a digestibility trial for 2weeks using Cr2O3 as inert marker, followed by a feeding trial for 4weeks. For the entire duration, juvenile trout from the two lines were fed diets with or without gelatinized starch. Blood, pyloric ceca, midgut and hindgut were sampled at 24h after the last meal. Transcripts of the proteins involved in nutrient transport and fatty acid bioconversion were abundant in the proximal intestine. GLUT2 transcripts were slightly higher in the F line ceca than in the L line. Dietary starch intake did not enhance the transcription of intestinal glucose transporters, SGLT1 and GLUT2; but it was associated with the higher expression of ApoA1 and PepT1 in the midgut. Significantly, the F line exhibited higher intestinal mRNA levels of MTP, ApoA4, Elovl2, Elovl5 and D6D than the L line, linked to chylomicron assembly and fatty acid bioconversion. Apparent digestibility coefficients of protein, lipid and starch were high in both lines, but not significantly different between them. In conclusion, we found a higher potential of chylomicron synthesis and fatty acid bioconversion in the intestine of F line, but no adaptive transcriptional response of glucose transporters to dietary starch and no genotypic differences in nutrient digestibility.

Trout oral VP2 DNA vaccination mimics transcriptional responses occurring after infection with infectious pancreatic necrosis virus (IPNV)

Time-course and organ transcriptional response profiles in rainbow trout Oncorhynchus mykiss were studied after oral DNA-vaccination with the VP2 gene of the infectious pancreatic necrosis virus (IPNV) encapsulated in alginates. The profiles were also compared with those obtained after infection with IPNV. A group of immune-related genes (stat1, ifn1, ifng, mx1, mx3, il8, il10, il11, il12b, tnf2, mhc1uda, igm and igt) previously selected from microarray analysis of successful oral vaccination of rainbow trout, were used for the RTqPCR analysis. The results showed that oral VP2-vaccination qualitatively mimicked both the time-course and organ (head kidney, spleen, intestine, pyloric ceca, and thymus) transcriptional profiles obtained after IPNV-infection. Highest transcriptional differential expression levels after oral vaccination were obtained in thymus, suggesting those might be important for subsequent protection against IPNV challenges. However, transcriptional differential expression levels of most of the genes mentioned above were lower in VP2-vaccinated than in IPNV-infected trout, except for ifn1 which were similar. Together all the results suggest that the oral-alginate VP2-vaccination procedure immunizes trout against IPNV in a similar way as IPNV-infection does while there is still room for additional improvements in the oral vaccination procedure. Some of the genes described here could be used as markers to further optimize the oral immunization method.

Structural and functional characterization of pituitary adenylyl cyclase-activating polypeptide (PACAP)/PACAP-related peptide (PRP) and its receptor in olive flounder (Paralichthys olivaceus)

We identified full-length cDNAs encoding pituitary adenylyl cyclase-activating polypeptide (PACAP), PACAP-related peptide (PRP), and PACAP-specific receptor (PAC1R) from olive flounder, Paralichthys olivaceus. Two variant mRNA forms were created by alternative splicing. Comparison of genomic and cDNA sequences of the PRP-PACAP precursor revealed that skipping of exon 4 within PRP resulted in two variant transcripts: a long form encoding both PRP and PACAP and a short form encoding PACAP only. Both transcripts were constitutively observed only in the brain, whereas the short form appeared in gut tissues, such as the intestine and pyloric cecum in fish challenged with a pathogen, but not in healthy fish. Furthermore, expression of the long PRP/PACAP transcript gradually increased in the intestine of flounder challenged with bacteria, suggesting that PRP and/or PACAP may serve as a regulator(s) of the immune system, especially in the gastrointestinal tract of olive flounder. The biological functions of PACAP and PRP were investigated by exogenous treatment of flounder embryogenic cells (hirame natural embryonic cells, HINAE cells) with synthetic peptides of fPACAP-38 and/or fPRP-45. Intracellular cyclic adenosine monophosphate (cAMP) production in PAC1R-overexpressing HINAE cells was regulated by fPACAP-38 in a concentration-dependent manner, but was not regulated by fPRP-45. Results from real-time quantitative polymerase chain reaction revealed that PAC1R mRNA was specifically induced by fPACAP-38 but not by fPRP-45; PACAP significantly increased TNF-α mRNA but not growth hormone (GH) mRNA in HINAE cells; however, PRP affected GH but not TNF-α mRNA expression. These results suggest that the expression ratio of PRP and PACAP is regulated at the transcriptional level depending on the tissues and conditions, and that the unique biological roles of PRP and PACAP differ from that of mammalian PRP.

Proteome Analysis of Pyloric Ceca: A Methodology for Fish Feed Development?

Changing the protein source of fish feed from fish meal to alternative sources of protein will affect traits such as fish growth, quality, and feed utilization. The present investigation was initiated to introduce a two-dimensional gel electrophoresis based proteomic workflow as a tool to investigate feed effects on fish by analyzing protein changes in the fish gut. The workflow was used to study the effect of substituting fish meal in fish feed by alternative sources of protein. Rainbow trout divided into five groups were fed for 72 days with feeds varying in protein composition. By two-dimensional gel electrophoresis proteins extracted from the pyloric ceca were separated, making it possible to measure the abundance of more than 440 protein spots. The expression of 41 protein spots was found to change due to differences in feed composition. By mass spectrometry 31 of these proteins were identified, including proteins involved in digestion (trypsinogen, carboxylic ester hydrolase, and aminopeptidase). The many expression changes indicated that the trout, when adapting to differences in feed formulation, alter the protein composition of the gut.

Oral immunization of rainbow trout to infectious pancreatic necrosis virus (Ipnv) induces different immune gene expression profiles in head kidney and pyloric ceca

Induction of neutralizing antibodies and protection by oral vaccination with DNA-alginates of rainbow trout Oncorhynchus mykiss against infectious pancreatic necrosis virus (IPNV) was recently reported [1]. Because orally induced immune response transcript gene profiles had not been described yet neither in fish, nor after IPNV vaccination, we studied them in head kidney (an immune response internal organ) and a vaccine entry tissue (pyloric ceca). By using an oligo microarray enriched in immune-related genes validated by RTqPCR, the number of increased transcripts in head kidney was higher than in pyloric ceca while the number of decreased transcripts was higher in pyloric ceca than in head kidney. Confirming previous reports on intramuscular DNA vaccination or viral infection, mx genes increased their transcription in head kidney. Other transcript responses such as those corresponding to interferons, their receptors and induced proteins (n=91 genes), VHSV-induced genes (n=25), macrophage-related genes (n=125), complement component genes (n=176), toll-like receptors (n=31), tumor necrosis factors (n=32), chemokines and their receptors (n=121), interleukines and their receptors (n=119), antimicrobial peptides (n=59), and cluster differentiation antigens (n=58) showed a contrasting and often complementary behavior when head kidney and pyloric ceca were compared. For instance, classical complement component transcripts increased in head kidney while only alternative pathway transcripts increased in pyloric ceca, different β-defensins increased in head kidney but remained constant in pyloric ceca. The identification of new gene markers on head kidney/pyloric ceca could be used to follow up and/or to improve immunity during fish oral vaccination.

Proteins and Enzymes from Marine Resources

Sea products are valuable resources of natural substances such as lipids, polysaccharides, enzymes, vitamins, and proteins. In this issue, a variety of fish proteases (trypsin, alcalase, etc.) have been characterized and sometimes purified. Many of these enzymes display potentially interesting new biochemical properties for industrial applications. Their potential adequacy for biotechnological applications such as chitin extraction was demonstrated. Biochemical characteristics of crude alkaline protease extracts from the viscera of goby (Zosterisessor ophiocephalus), thornback ray (Raja clavata), and scorpionfish (Scorpaena scrofa) were studied. At least four caseinolytic proteases bands were observed in zymogram of each enzyme preparation. These proteolytic preparations were successfully used in the deproteinization of shrimp wastes for chitin extraction. Furthermore, a trypsin was purified from the pyloric ceca of Pacific cod (Gadus macrocephalus) using chromatographic methods. The cod trypsin was successfully applied to catalyze dipeptide synthesis using series of “inverse substrates.” A Mackerel trypsin was also purified from defatted viscera by supercritical carbon dioxide, and its biochemical properties were studied. Recent biotechnological progresses require the research of new bioactive peptides from natural resources that can be used as an alternative to chemical products in various applications (food, cosmetics, drugs, etc.). Sea products proteins digestion using bacterial proteases generated protein hydrolysates displaying interesting biochemical properties and antioxidant activity. Antioxidative activities and biochemical properties of protein hydrolysates with different hydrolysis degrees, prepared from cuttlefish (Sepia officinalis) using an Alcalase and Bacillus licheniformis NH1 proteases were determined. The antioxidant activities of cuttlefish protein hydrolysates increased with increasing the hydrolysis degree. Antioxidative activity was concentration dependent. Furthermore, both Alcalase and NH1 protein hydrolysates were able to retard lipid peroxidation and β-carotene-linoleic acid oxidation. In addition, cuttlefish protein hydrolysates have a high percentage of essential amino acids and could be used as supplement to poorly balanced dietary proteins. Furthermore, carbohydrate-binding lectins were also extracted from many marine resources. This issue highlights the potential of sea products as valuable resources of bioactive peptides and proteins such as hydrolytic enzymes, lectins, and antioxidants. These resources might be of great interest for industrial biotechnological processes using safe and natural materials such as peptides or enzymes. Dicer is an RNase III enzyme with two catalytic subunits, which catalyzes the cleavage of double-stranded RNA to small interfering RNAs and micro-RNAs, which are mainly involved in invasive nucleic acid defense and endogenous genes regulation. In addition, Dicer is thought to be involved in defense mechanism against foreign nucleic acids such as viruses. A paper focused on the recent progress of Dicer-related research and discussed potential RNA interference pathways in aquatic species. Dicer is abundantly expressed in embryos, indicating the importance of the protein in early embryonic development. Nabil Miled Moncef Nasri Hideki Kishimura Faouzi Ben Rebah

Purification and characterization of trypsin from the pyloric ceca of orange-spotted grouper, Epinephelus coioides

Trypsin from the pyloric ceca of orange-spotted grouper, Epinephelus coioides, was purified by fractionation with ammonium sulfate, ionic exchange, and affinity chromatography. The protein was purified 161.85-fold with a yield of 4%. Purified trypsin had an apparent molecular weight of 24kDa according to an SDS-PAGE analysis. Optimal profiles of temperature and pH of the enzyme were 50°C and 8-10, respectively, using Nα-benzoyl-L: -arginine ethyl ester as the substrate. The results of thermal and pH stability assays showed that the enzyme was stable at temperatures of up to 50°C and in the pH range of 6-8. Trypsin activity decreased with an increasing NaCl concentration (0-0.6M). The activity of purified trypsin was effectively inhibited by a soybean trypsin inhibitor and N-p-tosyl-L: -lysine chloromethyl ketone, and was slightly inhibited by iodoacetic acid, ethylenediaminetetraacetic acid, 1-(L: -trans-epoxysuccinyl-leucylamino)-4-guanidinobutane, and pepstatin A. Protein identification of the purified protease showed that the sequences of two peptides, LGEHNI and NLDNDIML, were highly homologous to other fish trypsins. The measurement of trypsin activity in different tissues showed that the highest activity was detected in pyloric ceca, followed by anterior intestine, middle intestine, hind intestine and spleen, but very low activities were found in other tissues. An inverse relationship between the trypsin activity in four tissues of pyloric ceca, anterior intestine, middle intestine and hind intestine and fish body weight as a result of increased pepsin in stomach indicated grouper growth status was increased.

Cold-adapted structural properties of trypsins from walleye pollock (Theragra chalcogramma) and Arctic cod (Boreogadus saida)

Complementary DNA clones encoding trypsins were isolated from pyloric ceca of cold-adapted fish, walleye pollock (Theragra chalcogramma) (WP-T) and Arctic cod (Boreogadus saida) (AC-T). The isolated full-length cDNA clones of WP-T and AC-T were 852 and 860 bp, respectively, and both cDNAs were contained an open reading frame of 726 bp. WP-T and AC-T seemed to be synthesized as preproenzyme that contains a signal peptide, an activation peptide, and a mature trypsin. Although the amino acid sequence identities of WP-T and AC-T to that of bovine trypsin were 64 and 63%, respectively, they completely conserved the structural features for catalytic function of trypsin. On the other hand, WP-T and AC-T possessed the four Met residues (Met135, Met145, Met175 and Met242) in their molecules and the deletion of Tyr151 and substitution of Pro152 for Gly in their autolysis loops when aligned with the sequences of tropical-zone fish and bovine trypsins. In addition, the contents of charged amino acid residues at the N-terminal regions (positions 20–50) of WP-T and AC-T were extremely higher than those of other fish and bovine trypsins. Moreover, one amino acid (Asn72) and two amino acids (Asn72 and Val75) coordinating with Ca2+ in bovine trypsin were exchanged for another amino acids in WP-T (His) and AC-T (His and Glu), respectively, and the contents of negative charged amino acids at their Ca2+-binding regions were lower than those of tropical-zone fish and bovine trypsins. Therefore, it was considered that these structural characteristics of WP-T and AC-T are closely related to their lower thermostability.

Different utilization of plant sources by the omnivores jundiá catfish (Rhamdia quelen) and Nile tilapia (Oreochromis niloticus)

Plant sources are receiving special attention as feedstuffs in aquafeeds because of fish meal and oil shortage. However, studies about the effects of dietary fibre in fish are scarce. The inclusion of plant ingredients containing different levels of dietary fibre – broken rice (BR), ground corn (GC), wheat bran (WB), citrus pulp (CP) and soybean hulls (SH) were evaluated for the omnivores jundia catfish and Nile tilapia. Tilapia is a typical omnivore with long intestines, whereas jundia has short intestines and no pyloric ceca. Fibrous sources (CP, WB and SH) were less digestible for both species than the starchy ones (BR and GC). However, jundia presented less ability to utilize the starch and protein from plant sources than tilapia. Growth of tilapia followed plant sources digestibility but no significant differences were detected for jundia, probably because of its slower growth rate. Muscle layer was thicker in the distal intestine of jundia fed CP diet, which possibly indicates an adaptation to propel the large volume of viscous digesta along the intestine. Therefore, despite its lower ability to utilize starchy plant sources, jundia showed an adaptive capacity to utilize fibrous diets, which is in agreement with its omnivorous feeding habit.

Ontogeny of salinity tolerance and evidence for seawater-entry preparation in juvenile green sturgeon, Acipenser medirostris

We measured the ontogeny of salinity tolerance and the preparatory hypo-osmoregulatory physiological changes for seawater entry in green sturgeon (Acipenser medirostris), an anadromous species occurring along the Pacific Coast of North America. Salinity tolerance was measured every 2weeks starting in 40-day post-hatch (dph) juveniles and was repeated until 100% survival at 34‰ was achieved. Fish were subjected to step increases in salinity (5‰12h(-1)) that culminated in a 72-h exposure to a target salinity, and treatment groups (0, 15, 20, 25, 30, 34‰; and abrupt exposure to 34‰) were adjusted as fish developed. After 100% survival was achieved (134dph), a second experiment tested two sizes of fish for 28-day seawater (33‰) tolerance, and gill and gastrointestinal tract tissues were sampled. Their salinity tolerance increased and plasma osmolality decreased with increasing size and age, and electron microscopy revealed three types of mitochondria-rich cells: one in fresh water and two in seawater. In addition, fish held on a natural photoperiod in fresh water at 19°C showed peaks in cortisol, thyroid hormones and gill and pyloric ceca Na(+), K(+)-ATPase activities at body sizes associated with seawater tolerance. Therefore, salinity tolerance in green sturgeon increases during ontogeny (e.g., as these juveniles may move down estuaries to the ocean) with increases in body size. Also, physiological and morphological changes associated with seawater readiness increased in freshwater-reared juveniles and peaked at their seawater-tolerant ages and body sizes. Their seawater-ready body size also matched that described for swimming performance decreases, presumably associated with downstream movements. Therefore, juvenile green sturgeon develop structures and physiological changes appropriate for seawater entry while growing in fresh water, indicating that hypo-osmoregulatory changes may proceed by multiple routes in sturgeons.

First Records of Known Endoparasitic Species of Pseudempleurosoma Yamaguti, 1965 (Monogenoidea: Dactylogyridae) from Tetraodontid and Rachycentrid Fish Off the Northern Coast of the Yucatan Peninsula, Mexico

Monogenoideans infecting the rectum of the wild checkered puffer fish, Sphoeroides testudineus (Tetraodontidae), and the pyloric ceca of the cultured cobia, Rachycentron canadum (Rachycentridae), from the northern coast of the Yucatan Peninsula, Mexico, were morphologically identified as Pseudempleurosoma carangis Yamaguti, 1965 and Pseudempleurosoma gibsoni Santos, Mourão and Cárdenas, 2001 (Dactylogyridae), respectively. Morphometric comparison between the paratypes of P. carangis and those from S. testudineus showed that the latter differ only in the length of the body, germarium, and dorsal anchors. Similarly, a small form of P. gibsoni based on body size was detected in the present study. These metric differences may be attributable to the host effect, i.e., S. testudineus/R. canadum versus Caranx lugubris (Carangidae) (type host of P. carangis) from Hawaii and Paralonchurus brasiliensis (Sciaenidae) (type host of P. gibsoni) from Brazil, or by the degree of maturity, or both. In view of these considerations, new illustrations and several supplemental observations for P. carangis and P. gibsoni are provided. The present findings also represent new geographical records, and new sites of infection, e.g., rectum and pyloric ceca, for species of Pseudempleurosoma, and the first known endoparasitic monogenoideans infecting tetraodontid and rachycentrid fishes in Mexico.

Comparative morphology and cytology of the alimentary tract in lizardfishes (Teleostei, Aulopiformes, Synodontidae)

AbstractFishelson, L., Golani, D., Russell, B., Galil, B. and Goren, M. 2012. Comparative morphology and cytology of the alimentary tract in lizardfishes (Teleostei, Aulopiformes, Synodontidae). —Acta Zoologica (Stockholm) 93: 308–318.This study compares the morphology and cytology of the alimentary tract in several species of lizardfishes (Synodontidae, Teleostei) of the genera Saurida, Synodus, and Trachinocephalus, in relation to their diets and bathymetric distribution. All the studied species feature a large, pouch‐like stomach, with the intestine beginning at the stomach’s anterior apex, adjacent to the esophageal opening. In the more ‘microphagous’Synodus spp. and Trachinocephalus, the intestine bends twice before reaching the anus, whereas in the more ‘macrophagous’Saurida spp., the intestine extends straight to the anus. The species differ also in the number and form of their pyloric ceca, the length of the intestine and in the percentile relationship between stomach length and standard body length. Along the alimentary tract folds and villi protrude into the lumen, their numbers differing on various sites of the tract. Three cell types make up the gastric gland system: (1) pyramidal cells forming the tubular gastric glands in the lamina propria; among them are large, pale secretary cells; (2) groups of neck cells that surround the pits of the tubules; and (3) groups of large and granule‐rich cells at the end portion of the stomach. All species are carnivorous and uniform in morphology, the differences in the alimentary tract found between the more shallow‐water species of Synodus and Trachinocephalus, and the deeper‐dwelling Saurida, seem to be only partly correlated with the differences in diet.