Gut morphology in growth hormone transgenic Atlantic salmon

Growth hormone transgenic Atlantic salmon Salmo salar reared at 12–13°C were F₂ generation derived, using eggs from a transgenic F₁ female and fertilized with milt from a non-transgenic male. At the time of tissue sampling the transgenic salmon were growing 1·6 times faster than control salmon. Transgenic salmon tended to have more intestinal folds that were longer than those of control salmon. Consequently, the transgenic salmon had a larger digestive surface area both in the anterior intestine (surface area 1·5 times control) and in the pyloric caeca (surface area 1·2 times control). Most morphological features of the intestine and of the pyloric caeca of transgenic salmon were larger than those of control salmon; in particular, the surface area of the anterior intestine was concordant with the growth rate difference.     

野生与养殖黄鳍鲷消化道形态组织结构

采用常规石蜡组织切片的方法对野生和养殖黄鳍鲷(Sparus latus)消化道的形态组织结构进行了比较观察。结果表明,野生和养殖黄鳍鲷的消化道存在一定差异。(1)形态学研究表明,食道粗而短,胃呈V形,分为贲门部、胃体部和幽门部,胃与肠的连接处有4条幽门盲囊,肠道在体腔内迂回两个回折。野生黄鳍鲷牙齿更为坚硬锋利,体腔中脂肪较少,消化道更为粗短。野生和养殖黄鳍鲷的肠道系数分别为0.71±0.03和0.94±0.12。(2)组织学研究表明,食道黏膜上皮由扁平细胞层和杯状细胞层组成,杯状细胞发达。胃黏膜由单层柱状上皮组成,无杯状细胞,贲门部和胃体部胃腺发达。幽门盲囊组织学特征与肠相似,上皮为柱状上皮,其中的杯状细胞少于肠。肠中,前肠杯状细胞最多,中肠次之,后肠最少。直肠杯状细胞多于肠。野生与养殖黄鳍鲷组织学的区别在于,消化道相同部位养殖鱼的杯状细胞多于野生鱼,野生鱼的肌层厚度大于养殖鱼。黄鳍鲷消化道的形态组织结构与其生活环境和食物是相关的。     

Phylogenetic analysis of intestinal microflora indicates a novel Mycoplasma phylotype in farmed and wild salmon

All studies of the microbial community of the gastrointestinal tract of salmon to date have employed culture-based approaches, typically on pond- or tank-raised, freshwater animals. We present a phylogenetic survey of the bacterial populations present in the distal intestine of salmon from three different marine locations in Europe. This was accomplished through PCR amplification, cloning, and sequencing of partial 16S rDNA genes from microbial community DNA isolated from the contents of the GI tract distal to the pyloric ceca. Using this approach, the intestinal microbial communities of wild salmon from Scotland and pen-raised salmon from Scotland and Norway were compared. The predominating bacterial populations detected were Acinetobacter junii and a novel Mycoplasma phylotype. This Mycoplasma phylotype apparently comprised ~96% of the total microbes in the distal intestine of wild salmon. Substantial differences in intestinal microbial community composition and diversity were observed between the two groups of pen-raised salmon, which, in addition to geographical separation, were raised on different feeds. The microbial profiles found in this study were substantially different from those indicated in earlier culture-based studies for several species of fish, presumably because of the culture-independent techniques employed. Further, analysis of short-chain fatty acids in the digestive tract indicated that the decreasing redox gradient from proximal to distal reaches common to homeothermic animals was absent in salmon, and that the bacterial fermentation levels were much lower than are reported in homeothermic animals.     

Effects of diets containing soybean meal on trypsin mRNA expression and activity in Atlantic salmon (Salmo salar L)

Atlantic salmon develop subacute enteritis in the distal intestine (DI) when fed diets containing soybean meal (SBM) at high levels, a condition accompanied by increased trypsin activity in the DI intestinal content compared to fish fed conventional fishmeal (FM) based diets. To further investigate the responses of Atlantic salmon to dietary SBM, we measured trypsin activity in intestinal contents, quantified pancreatic trypsin mRNA expression, surveyed trypsin mRNA expression in selected tissues and characterized active forms of trypsin in the intestinal wall and brain. Enzyme measurements showed that trypsin activity in the intestinal content of SBM fed fish was lower in the proximal segments of the intestine, but higher in the DI compared to FM fed fish. The difference in enzyme activity was not reflected in a differential expression of pancreatic trypsin mRNA between fish fed the different diets (FM or SBM). Trypsin mRNA was expressed in 18 different tissues (esophagus, stomach, pancreas, pyloric tissue, midintestine, distal intestine, liver, head kidney, kidney, heart, spleen, thymus, brain, eye, gills, gonads, muscle and skin) but was most prominently expressed in tissues of the gastrointestinal (GI) tract and brain. We report for the first time an upregulation of trypsin-like activity in the DI wall using an in-gel trypsin activity assay, as well as modulated activity in the brain of fish fed SBM. The increased activity in the DI wall may contribute to disease severity and higher trypsin activity in the intestinal content.     

Intestinal transport of fructose and glycine in Ophiocephalus punctatus.

The regional variations in the absorption of fructose and glycine have been studied in the intestine and pyloric caeca of the fish, Ophiocephalus punctatus in vivo, by preparing intestinal sacs. Diffusion of amino acids out of the intracellular compartment of the intestine was observed in all the portions of the intestine. The pyloric caeca showed maximum transport of fructose. Absorption of fructose was slightly more in the posterior intestine than in the anterior intestinal sac. Maximum transport of glycine took place in the anterior intestinal sac. Pyloric caeca adsorbed more glycine than did the posterior sac. For both nutrients, the rate of uptake did not differ significantly in the upper and the lower portion of the intestine. In all the portions, the transport of fructose was more rapid than that of glycine. The experiments revealed that though the nutrients are absorbed in the entire length of the intestine, the quantity absorbed varies from one portion to another and is dependent on the nature of the compound absorbed.     

Ontogeny of the Digestive System of Atlantic Salmon (Salmo salar L.) and Effects of Soybean Meal from Start-Feeding

Despite a long history of rearing Atlantic salmon in hatcheries in Norway, knowledge of molecular and physiological aspects of juvenile development is still limited. To facilitate introduction of alternative feed ingredients and feed additives during early phases, increased knowledge regarding the ontogeny of the digestive apparatus in salmon is needed. In this study, we characterized the development of the gastrointestinal tract and accessory digestive organs for five months following hatch by using histological, biochemical and molecular methods. Furthermore, the effects of a diet containing 16.7% soybean meal (SBM) introduced at start-feeding were investigated, as compared to a fishmeal based control diet. Salmon yolk sac alevins and fry were sampled at 18 time points from hatch until 144 days post hatch (dph). Histomorphological development was investigated at 7, 27, 46, 54 and 144 dph. Ontogenetic expression patterns of genes encoding key digestive enzymes, nutrient transporters, gastrointestinal peptide hormones and T-cell markers were analyzed from 13 time points by qPCR. At 7 dph, the digestive system of Atlantic salmon alevins was morphologically distinct with an early stomach, liver, pancreas, anterior and posterior intestine. About one week before the yolk sac was internalized and exogenous feeding was started, gastric glands and developing pyloric caeca were observed, which coincided with an increase in gene expression of gastric and pancreatic enzymes and nutrient transporters. Thus, the observed organs seemed ready to digest external feed well before the yolk sac was absorbed into the abdominal cavity. In contrast to post-smolt Atlantic salmon, inclusion of SBM did not induce intestinal inflammation in the juveniles. This indicates that SBM can be used in compound feeds for salmon fry from start-feeding to at least 144 dph and/or 4-5 g body weight.     

Spawning behaviour of a farmed escaped female Atlantic salmon (Salmo salar)

Excavation of stranded redds revealed differences in spawning behaviour between farmed and wild Atlantic salmon. The redd of a farmed fish contained more egg pockets (nine v . average of two) and fewer eggs per pocket (averages: 459 v . 707). No other pocket measures differed.     

Temporal stability of sea louse Lepeophtheirus salmonis Krøyer populations on Atlantic salmon Salmo salar L. of wild, farm and hybrid parentage

Atlantic salmon salmo salar smolts of wild, hybrid and farmed parentage were individually tagged then reared in a sea cage for 8 months. The fish were sampled three times during this period. On all occasions, farmed Atlantic salmon displayed the highest abundance and density of sea lice Lepeophtheirus salmonis , whilst no significant differences were observed between hybrid and wild Atlantic salmon. Percentage variation between the lowest and highest infected groups was as high as 175 and 144% for L. salmonis abundance and density respectively (sample 2). The temporal stability of interindividual sea lice infection levels was investigated pair‐wise between samples using correlation (sample 1 v . 2, 1 v . 3 and 2 v . 3). When calculated using sea louse abundance, correlations ranged from r ² = 0·11, P  < 0·01 to r ² = 0·39, P  < 0·001, but, when the effects of fish size were controlled for by converting abundance to density, all correlations were <  r ² = 0·1. Therefore, these data indicate that a fish's relative infection level in one sample was a weak predictor of its relative infection level in another sample. This suggests that identification of individual Atlantic salmon that display reduced susceptibility to sea lice, may be problematic.     

Gross anatomical and histomorphological features of the Acanthopagrus schlegelii digestive tract (Bleeker 1854) Perciformes,Sparidae

Acanthopagrus schlegelii is an autochthonous teleost species concerning the remarkable economic importance and prevalent fish cultivated in China as well as in different nations of South-East Asia. Little is known about the digestive tract (DT) morphology of A. schlegelii. Therefore, anatomical and histomorphological aspects of A. schlegelii DT were examined by light and scanning electron microscope (SEM). Anatomically, DT of A. schlegelii was mainly formed of oesophagus, well-developed stomach and fingers like pyloric caeca (four in number), intestinal regions and rectum. Histomorphologically, oesophagus occurred as a shorter tube-like organ presenting a longitudinal folded mucosa that connects oropharynx cavity to stomach. Stomach was a muscular thick-wall organ that included three regions, thickly longitudinal folds were observed in the first (cardiac) and last (pyloric) regions, whereas the second (fundic) region showed folds in different directions. Long villi were observed within pyloric caeca and anterior intestine. Tunica muscularis appeared narrow in the anterior intestine, whereas thicker in the posterior part of the intestine. Collectively, anatomical and histomorphological aspects of A. schlegelii DT are consistent with the carnivorous habit of this species. These data could be a potential source to modify better methods of nutrition and identify the DT pathogenic conditions in farming of this fish.     

Migratory behaviour of wild and farmed Atlantic salmon (Salmo salar) during spawning

Migratory behaviour at spawning of wild and newly-escaped farmed Atlantic salmon was analysed by radio telemetry in the River Alta, North Norway. Spawning areas were located by aerial surveys. Farmed females moved significantly more than wild females ( P <0.01). There was no such difference between the two groups of males. About 83% of the wild fish stayed within identified spawning areas for 1 day or longer. The corresponding figure for farmed salmon was only 43% ( P <0.05). Wild salmon stayed 8.1 days inside spawning areas and farmed salmon 5.2 days. The present results suggest that escaped farmed salmon had reduced spawning success compared with wild fish.     

Salmon lice increase the age of returning Atlantic salmon

The global increase in the production of domestic farmed fish in open net pens has created concerns about the resilience of wild populations owing to shifts in host–parasite systems in coastal ecosystems. However, little is known about the effects of increased parasite abundance on life-history traits in wild fish populations. Here, we report the results of two separate studies in which 379 779 hatchery-reared Atlantic salmon smolts were treated (or not) against salmon lice, marked and released. Adults were later recaptured, and we specifically tested whether the age distribution of the returning spawners was affected by the treatment. The estimates of parasite-induced mortality were 31.9% and 0.6% in the River Vosso and River Dale stock experiments, respectively. Age of returning salmon was on average higher in treated versus untreated fish. The percentages of fish returning after one winter at sea were 37.5% and 29.9% for the treated and untreated groups, respectively. We conclude that salmon lice increase the age of returning salmon, either by affecting their age at maturity or by disproportionately increasing mortality in fish that mature early.     

Differences in digestion and absorption of dietary protein in Atlantic salmon (Salmo salar) with genetically different trypsin isozymes

Digestion and absorption of dietary protein were studied through facilitation of amino acid in the plasma and white muscle after a single feeding. The comparison was made between Atlantic salmon with and without trypsin isozyme TRP-2*92. Higher absorption of dietary protein was associated with the presence of the isozyme, as the post-prandial total levels of free amino acids (FAA) in both plasma and white muscle were significantly higher in salmon with the isozyme than those in salmon without it. Higher digestion rate of the dietary protein in salmon carrying the isozyme was indicated by faster elevation of essential FAA in the plasma and of overall FAA in their white muscle. Other indications which suggest differences in nitrogen metabolism between salmon with and without the isozyme were the observations of significant differences in (a) the levels of lysine, hydroxyproline, alanine, aspartic acid, β-alanine, threonine, valine and a nitrogen-containing compound taurine in plasma, and (b) the levels of alanine, glutamic acid, glycine and anserine in white muscle.
Trypsin activity in the pyloric caeca showed less response to feeding than that in the intestine, but it may have consequence for growth as its activity was significantly higher in growing fish than in non-growing fish.     

Phenotypic flexibility of digestive system in Atlantic cod (Gadus morhua)

This study examined the restoration of the digestive capacity of Atlantic cod (Gadus morhua Linnaeus) following a long period of food deprivation. Fifty cod (48 cm, 1 kg) were food-deprived for 68 days and then fed in excess with capelin (Mallotus villosus Müller) on alternate days. Ten fish were sampled after 0, 2, 6, 14 and 28 days and the mass of the pyloric caeca, intestine and carcass determined. Two metabolic enzymes (cytochrome c oxidase and citrate synthase) were assayed in white muscle, pyloric caeca and intestine, and trypsin activity was measured in the pyloric caeca. A delay of 14 days was required before body mass started to increase markedly, whereas most of the increase in mass of both the pyloric caeca and intestine relative to fish length occurred earlier in the experiment. By day 14, the activities of trypsin and citrate synthase in the pyloric caeca as well as citrate synthase in the intestine had reached maxima. The growth of the digestive tissues and restoration of their metabolic capacities thus occur early upon refeeding and are likely required for recovery growth to take place. The phenotypic flexibility of the cod digestive system is therefore remarkable: increases in trypsin activity and size of pyloric caeca resulted in a combined 29-fold increase in digestive capacity of the fish during the refeeding period. Our study suggests that Atlantic cod are able to cope with marked fluctuations in food availability in their environment by making a rapid adjustment of their digestive capacity as soon as food availability increases.     

Determination of carotenoid and vitamin A concentrations in everted salmonid intestine following exposure to solutions of carotenoid in vitro

Carotenoid (astaxanthin and canthaxanthin) concentrations in everted intestine from rainbow trout (Oncorhynchus mykiss, Walbaum) and Atlantic salmon (Salmo salar, L.) exposed to micelle solubilised carotenoid, have been determined. Following exposure (1 h) to astaxanthin solution (5 mg l(-1)), trout pyloric caeca and mid intestine had higher (P<0.05) mean tissue astaxanthin concentrations (0.50+/-0.08 microg g(-1) and 0.54+/-0.09 microg g(-1), respectively) compared to hind intestine (0.04+/-0.01 microg g(-1); n=11+/-S.E.). Furthermore, the astaxanthin concentration in pyloric caeca (0.50+/-0.08 microg g(-1)) was greater (P<0.05) than that of canthaxanthin (0.11+/-0.01 microg g(-1); n=11, +/-S.E.) when exposed to solutions of similar carotenoid concentration (5.11+/-0.16 mg l(-1) and 5.35+/-0.16 mg l(-1), respectively; n=3+/-S.E.). However, no differences (P>0.05) were recorded between trout and salmon intestinal tissue in terms of astaxanthin concentration following exposure. Trout caeca exposed to astaxanthin solution had significantly (P<0.05) more vitamin A (514.1+/-36.4 microg g(-1)) compared to control tissues (316.5+/-61.7 microg g(-1); n=8+/-S.E.). Vitamin A(1) concentrations in caeca (287.7+/-11.0 microg g(-1)) exposed to astaxanthin solution were significantly higher (P<0.05) compared to controls (174.9+/-26.9 microg g(-1)). However, vitamin A(2) concentrations were not significantly (P>0.05) different (226.3+/-28.2 microg g(-1) and 141.6+/-35.2 microg g(-1), respectively).     

Modeling Parasite Dynamics on Farmed Salmon for Precautionary Conservation Management of Wild Salmon

Conservation management of wild fish may include fish health management in sympatric populations of domesticated fish in aquaculture. We developed a mathematical model for the population dynamics of parasitic sea lice (Lepeophtheirus salmonis) on domesticated populations of Atlantic salmon (Salmo salar) in the Broughton Archipelago region of British Columbia. The model was fit to a seven-year dataset of monthly sea louse counts on farms in the area to estimate population growth rates in relation to abiotic factors (temperature and salinity), local host density (measured as cohort surface area), and the use of a parasiticide, emamectin benzoate, on farms. We then used the model to evaluate management scenarios in relation to policy guidelines that seek to keep motile louse abundance below an average three per farmed salmon during the March–June juvenile wild Pacific salmon (Oncorhynchus spp.) migration. Abiotic factors mediated the duration of effectiveness of parasiticide treatments, and results suggest treatment of farmed salmon conducted in January or early February minimized average louse abundance per farmed salmon during the juvenile wild salmon migration. Adapting the management of parasites on farmed salmon according to migrations of wild salmon may therefore provide a precautionary approach to conserving wild salmon populations in salmon farming regions.