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Abstract The study was carried out to evaluate wedge wire screen as a potential tool for collecting fish faeces from the tank outlet water. Apparent digestibility (AD) estimates of carbon (AD C), nitrogen (AD N), sulphur (AD S), organic material (AD ORG) and individual amino acids obtained by the wire screen were compared with stripping. Three diets, with fishmeal, soybean meal (SBM) or rapeseed meal (RSM) as main protein source were extruded and fed to triplicate groups of 120-g rainbow trout (Oncorhynchus mykiss). Faeces were obtained by gentle stripping from the distal abdomen, and by collection from a wedge wire screen 15, 30, 60, 120 and 240 min post feeding. AD ORG , AD N and AD S obtained by collection on the screen were significantly (P <.05) higher than those obtained by stripping, except for some values for AD C. Differences in AD between stripping and faeces collected with the wire screen were lower than reported for other methods of collection from water media. Most of the increase in AD of nutrients for wedge wire screen occurred during the first 15 min after defecation. The AD ORG , AD C , AD N and AD S were lowest in the RSM diet. The AD of amino acids followed the same pattern as AD N. AD S in the rapeseed diet was particularly low (54.7%), compared to the fishmeal (72.4%) and SBM diet (70.1%). In addition to AD of cysteine, low digestibility of glucosinolates, its degradation products and other sulfonated components are likely reasons for the low AD S. Faeces from the RSM based diet had higher dry matter (DM) concentration than the SBM based diet. Faecal DM recovery for SBM was lowest among the diets for both collection methods. The low DM recovery for the SBM faeces did not affect AD estimates of faeces at the different time intervals, possibly due to simultaneous leakage of nutrients and indigestible marker. In conclusion, the use of wedge wire screen for collection of faeces represents an interesting supplement to stripping. The AD estimates had low random variation and nutrient leaching during faeces collection were dependent on dietary composition. Highlights • The digestibility estimates from the wire screen had low variation within time points and dietary treatments. • Digestibility results obtained for faeces collected from water should not be used as indicator for fecal nutrient loss • Feed composition and characteristics play a significant role in nutrient loss from faeces. [ABSTRACT FROM AUTHOR]

An increase in salinity of the aquatic habitat can be an environmental stress factor for fresh aquatic organism, including fish. The present study investigated the impact of salinity and diet composition on digestibility and intestinal morphology of Nile tilapia. Triplicate groups of 35 fish weighing 35 g were fed a “Control” and “Test” diet and kept at salinity of 0‰ and 15‰ for 8 weeks. The diets were formulated using a different soybean meal content to create a contrast in alterations in intestinal morphology. Six fish per treatment were sampled for intestinal morphology analysis at the end of weeks 1, 4 and 8. The proximal, middle and distal intestine were processed for quantitative histology, in order to count the number of goblet cells and eosinophilic granulocytes; and to measure the thickness of lamina propria and sub-epithelia mucosa. The study showed that a salinity of 15‰ increased the nutrient digestibility; however this enhanced digestibility diminished over time. The intestinal morphology was influenced by both the salinity as well as the dietary soybean meal content. For soybean meal, the impact on morphology was largest in the proximal region of the intestine, whereas for salinity the largest impact was in the distal region. The negative effect of increased soybean meal on the lamina propria thickness was enhanced at a salinity of 15‰ and aggravated in time. Difference in nutrient digestibility induced by the salinity seemed not to be related to alterations in the intestinal morphology. [ABSTRACT FROM AUTHOR]

Carbohydrate utilization by fish varies with feeding habits and feed processing. Extruded aquafeeds have increased digestibility of carbohydrate sources resulting from the cooking and gelatinization of this nutrient, making it readily available for all aquatic species. This study aimed at determining the effects of extrusion cooking of feeds in the digestibility of different dietary carbohydrate sources for dourado. Isonitrogenous and isoenergetic diets (530 g kg−1 crude protein and 20.80 MJ kg−1 gross energy) containing either corn, toasted cassava flour, wheat flour, broken rice, cassava starch, or corn starch, in extruded or pelletized form and added of chromic oxide as inert marker, were fed to groups of juvenile dourado (73.97 ± 12.0 g; n = 40) stocked in 500-L polyethylene tanks. Extrusion cooking improved the digestibility of energy and/or starch of corn, cassava starch, wheat flour, rice and corn starch ( P < 0.05), but did not affect digestibility of toasted cassava flour ( P > 0.05). It is thus fair to infer that dourado, despite being a carnivorous species, is properly fit to digest wheat flour, rice and corn starch in natural form. [ABSTRACT FROM AUTHOR]

The serial replacement of fish meal (anchovetta) by canola meal (CM) (100, 200, 300 g kg − 1 as either solvent extracted (SE) CM or expeller extracted (EX) CM was undertaken to investigate the effects of increasing dietary CM levels on feed intake, growth, protein and energy retention, plasma biochemistry and the expression of a suite of hepatic genes in barramundi (Asian seabass; Lates calcarifer ) over an eight week feeding trial. An additional diet using lupin kernel meal (LM) to replace the fish meal was also included as a comparative reference. Eight iso-digestible nitrogenous (423 ± 29 g kg − 1 ) and iso-digestible energetic (14.6 ± 8 MJ kg − 1 DM) diets were formulated. Each diet was randomly allocated to triplicate groups of fish in seawater tanks (600 L), and each tank was stocked with 15 fish (53.4 ± 7.0 g). Fish were fed once daily (9:00–10:00) to apparent satiation, and uneaten feed was collected to determine feed consumption. The results showed that the survival, feed intake, growth, FCR, energy and protein retention of fish fed the diet containing SE CM were similar or even higher to those of fish fed the fish meal reference diet (FM) and the LM diet. Fish fed with the diet containing 300 g kg − 1 SE CM did not show any changes in biochemistry and gene expression in a suite of detoxification genes. However, the diet with 300 g kg − 1 EX CM depressed feed intake, growth performance and increased feed conversion ratio (FCR). Transcription of genes involving in fatty acid synthesis and the TCA cycle were not changed by different diets. The down regulation of gene expression in certain detoxification genes ( Lc CYP1A1 , Lc CYP3A , Lc CYP2N and Lc GST ) was observed in fish fed with the diet containing 300 g kg − 1 EX CM compared to the FM control diet and other experimental diets. In general, the SE CM can be used up to 300 g kg − 1 diet without negative performance effects or signs of clinical plasma biochemistry. By contrast the maximum acceptable level of the EX CM for barramundi was only 200 g kg − 1 . Higher inclusion level of the EX CM induced negative effects on growth performance, feed utilisation, plasma biochemistry and gene expression in relation to detoxification. Statement of relevance Previous research has demonstrated that canola meal is a potential plant protein source for fish meal replacement in diets for many fish species. The present work is designed to be the first to assess both two types of Australian canola meal in regard to different processing methods (solvent extraction and expeller extraction) in use for barramundi (Asian seabass) diets. The research not only assesses effects of canola meal on growth performance and feed utilisation but also investigate effects of canola meal use on fish health status using broad approach including plasma chemistry, histology and gene expression analysis. The present findings provide practical information for barramundi's diet formulation using canola meal as an additional plant ingredient. These also provide implications of potential health effects relating to using canola meal for barramundi. [ABSTRACT FROM AUTHOR]

Symptoms indicating digestive malfunction have been observed in cultivated salmon over the last 10–15 years, at least partially as a consequence of use of new feed ingredients. The present knowledge on many aspects of digestive functions in fish is limited, in particular for Atlantic salmon. Strengthening is needed to understand the mechanisms underlying challenges to gastrointestinal health and to find means to prevent their development. The present paper supplies information regarding digestive enzyme optima and stability, chyme pH and enzyme activities along the digestive tract of Atlantic salmon. The data presented includes new data from four studies on Atlantic salmon as well as a review of comparative literature from various other fish studies. The four experiments comprised salmon of different sizes, kept in salt or fresh water, and fed high fish meal diets with different protein to energy ratios (P/E). These studies showed an average pH in the stomach chyme, i.e. across diets and experiments, of 4.8 (SD = 0.7), whereas the observed pH optimum for pepsin was 3.0. In the intestinal chyme, pH increased throughout the intestine from a mean of 8.1 (SD = 0.23) in the proximal intestine to 8.4 in the mid intestine (SD = 0.27) and distal intestine (SD = 0.29). Total proteolytic activity of chyme in the proximal intestine, measured as the sum of the work of all proteolytic enzymes on casein as substrate, showed its maximum at pH 8.8, i.e. clearly above prevailing chyme pH. For the individual proteolytic enzymes, pH optimum varied from 7.10 for elastase 1 to 8.98 for trypsin. Chyme pH did not appear to be influenced by fish size, but was significantly higher in the fish raised in fresh water than in those raised in salt water. In the intestinal chyme pH showed a significant negative regression on diet P/E. For the investigated pancreatic enzymes in the intestinal chyme, the activity in the chyme decreased from proximal to distal regions and faecal activities were very low compared to the activities in the proximal intestine. The activity profile for leucine aminopeptidase (LAP), however, trended to increase from mid to distal intestine. Chyme enzyme activities along the intestinal tract did not differ clearly between the experiments and no clear relationship between P/E on enzyme activities along the intestinal tract was observed. Remarkable in vitro stability was observed for the proteolytic enzyme activities. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of diets with different plant protein ingredients on proximate composition, tissue metabolites and tissue fatty acid composition, as well as hepatic and intestinal histological modifications in Senegalese sole ( Solea senegalensis). Fish (21.5 ± 2.8 g body weight) were fed six isonitrogenous and isoenergetic diets during 11 weeks. A control diet containing fish meal as the main protein source was compared with five experimental diets replacing 30% fish meal protein by different plant protein sources: soybean meal ( SBM), soybean protein concentrate ( SPC), soybean protein isolate ( SPI), wheat gluten meal ( WGM) or pea protein concentrate ( PPC). The inclusion of different plant protein did not significantly affect growth and proximate composition of fish. The hepatosomatic index was not significantly different to the control group; however, utilization of WGM significantly increased hepatocyte size. Plasma protein values and muscle triglycerides were influenced by the inclusion of SBM and WGM in the diets respectively. Feeding fish on SBM, WGM and PPC diets significantly enhanced n-6 fatty acid levels in muscle, particularly linoleic acid. None of the plant protein ingredient used in the diets decreased arachidonic, eicosapentaenoic as well as docosahexaenoic acid values in liver and muscle. Overall, histological studies did not reveal the existence of any intestinal alterations induced by the inclusion of different plant proteins. Despite moderate changes produced by SBM, SPC and WGM, inclusion of dietary plant protein ingredients has no major impact on growth, tissue and blood biochemistry, fatty acid profile and gut integrity of Senegalese sole juveniles. [ABSTRACT FROM AUTHOR]

This is the first study investigating the plant-herbivore interaction between Sarpa salpa, which has overgrazed seagrass transplants in Portugal, and the seagrasses Cymodocea nodosa, Zostera marina and Zostera noltii, which have been considered for restoration. When offered the choice between the three seagrasses in outdoor tanks, adult S. salpa clearly preferred Z. noltii. Testing the seagrasses separately, mean ± s.d. feeding rates ranged from 21 ± 11 g seagrass fresh mass kg−1 fish mass day−1 for Z. marina to 32 ± 9 g seagrass fresh mass kg−1 fish mass day−1 for C. nodosa and 40 ± 11 g seagrass fresh mass kg−1 fish mass day−1 for Z. noltii (temperature = 16° C). Food-processing rate in S. salpa did not differ between seagrasses, and there was no evidence of a regulation of processing rate according to food intake. Seagrasses differed substantially in nitrogen content and C:N, with C. nodosa containing the highest nitrogen content and lowest C:N (2·5 ± 0·1% and 14·0 ± 1·0), followed by Z. noltii (2·1 ± 0·1% and 17·0 ± 1·0) and Z. marina (1·4 ± 0·1% and 26·0 ± 2·0). Food-processing rate in S. salpa and the nutritional value of the seagrasses were not correlated with the observed feeding preference and rate. The study suggests that C. nodosa and Z. marina are less at risk of overgrazing by S. salpa and might thus be preferable to Z. noltii for seagrass restoration in areas with noticeable abundances of this fish. [ABSTRACT FROM AUTHOR]

Modern feeds for industrial salmon farming are presently formulated to fulfill specific digestible protein (DP, grams per kg feed, hereafter called units) and digestible energy (DE, Mega Joule (MJ) per kg feed) specifications. In the present study, 299 feed samples and accompanying fecal samples were obtained from 43 different farming sites for Atlantic salmon along the coast of Norway between October 2010 and February 2013. Apparent digestibility coefficients for protein and fat were calculated from protein and fat in feed and fecal matter, using analyzed crude fiber contents as a digestibility marker. Overall mean apparent protein and fat digestibilities were 87.1% (±4.9; overall mean±S.D.) and 92.5% (±3.7), respectively. Linear mixed models with rearing site as random effect were applied to evaluate factors that influenced the apparent digestibility of protein and fat, feeding intensity and energy intake. Apparent digestibility of fat tended to increase over the study period, and both feed type and feed manufacturing company, and water temperature influenced the digestibility significantly. Digestible energy content (DE, MJ/kg) was significantly negatively associated with feeding intensity, but not with total digestible energy intake. Variation at site level was significant in all analyses, and was moderate for the digestibility analyses and high regarding feeding intensity and energy intake. Digestibility assessments were used to assess accuracy, precision and agreement between optimized and realized digestible protein (DP, %) and DE level of feeds, using the mean difference between the two sets of observations and a fixed contribution of dietary energy from starch. Overall mean difference between realized and optimized DP and DE was −0.28units and −0.56MJ/kg, respectively, and there were significant differences between feed manufacturing companies. The results indicated that field digestibility assessments can be used to validate nutritional and economical value of feeds in commercial salmon farming. [ABSTRACT FROM AUTHOR]

Abstract: The effects of dietary probiotics on growth performance, health status of the digestive system and on the blood parameters of juvenile rainbow trout (Oncorhynchus mykiss, Walbaum) were investigated. Compared to the controls, diets supplemented with Kocuria SM1 and Rhodococcus SM2 for 14days caused no significant (P>0.05) change on the growth of fish, although SM2 led to an increased specific growth rate. SM1 or SM2 started to colonize in the gut after 7days of administration reaching a maximum, i.e. ~90–100% of total bacterial population, at 14days. Yet, the probiotics disappeared from the gut once administration ceased. Structural differences were not noted in the pyloric caeca and foregut, but the overall condition of the midgut and hindgut improved in fish receiving probiotics. The profile of digestive enzymes, as determined by the use of API ZYM, and stress indicators, i.e. serum hemoglobin, urea, creatinine and glucose, was not affected by any of the experimental diets (P>0.05). [Copyright &y& Elsevier]

Abstract: To investigate the effect of dissolved oxygen level ([O2]) on maintenance metabolism, feeding metabolism, aerobic swimming performance and their metabolic interaction in juvenile southern catfish (Silurus meridionalis Chen), we measured the following: (1) the resting oxygen consumption rate (MO2rest) over a range of water [O2] and from this we calculated the critical oxygen tension (P crit) of fasting fish; (2) the postprandial MO2 response (10% body mass meal size) at water [O2] of 1, 2, 4 and 8mgO2 L−1; and (3) the swimming performance of fasting and digesting fish at water [O2] of 1, 2, 4 and 8mgO2 L−1 at 25°C. The MO2rest remained constant over a broad range of water [O2] but then dropped markedly upon reaching the P crit (16.4% saturation). Hypoxic groups presented lower peak postprandial MO2 (MO2peak) (1mgO2 L−1 group), larger energy expenditure and longer digestive process (both 1 and 2mgO2 L−1) than those of normoxic groups. Both critical swimming speed (U crit) and the active metabolic rate (MO2active) of fasting fish remained unchanged over a decrease in water [O2] from 8 to 4mgO2 L−1 and then decreased significantly with further decreases in water [O2]. These parameters in fed fish showed a pronounced decrease as water [O2] decreased from 8 to 1mgO2 L−1. Feeding caused a significantly lower U crit in the 2mgO2 L−1 water [O2] group, a significantly higher MO2active in both the 2 and 8mgL−1 water [O2] groups and a significantly higher metabolic scope (MO2active − MO2rest) in both the 2 and 4mgO2 L−1 water [O2] groups compared to fasting fish. The MO2 increased greatly with swimming speed in the higher water [O2] groups, whereas it leveled off as swimming speeds approached the U crit in the lower water [O2] groups. Within all water [O2] groups, feeding caused a higher MO2 compared to fasting fish when fish swam at the same speeds, except in the 1mgO2 L−1 group. This finding showed that the critical water [O2] for maintenance of metabolism, digestion, swimming and postprandial swimming increased sequentially due to the increasing O2 demand, which challenges respiratory capacity. With the administration of the medium-sized meal that was used in this study, the metabolic mode of juvenile southern catfish changed from an additive mode during normoxia to a digestion-priority mode under moderate hypoxia and to locomotion-priority mode under hypoxia. [Copyright &y& Elsevier]

Abstract: A 10-week feeding trial in seawater floating cages (1.5×1.5×2.0m) was conducted to investigate the effects of dietary canola meal (CM) levels on growth, survival, digestion and selected immune parameters of Japanese seabass (initial average weight 8.3±0.15g). Six isonitrogenous (crude protein 43%) and isoenergetic (20kJg− 1) practical diets were formulated by replacing 0 (the control), 10, 20, 30, 40, and 50% of protein from fish meal with CM. Each diet was randomly fed to triplicate groups of fish, and each cage was stocked with 20 fish. Fish were fed twice daily (06:30 and 16:30) to apparent satiation. The results showed that with increasing dietary CM levels, the survival, specific growth rate (SGR) and feed efficiency (FE) decreased. The survival was significantly lower compared to the control group (P <0.05) with a 40% substitution level. Fish fed the diet with 20% or more protein from CM had significantly lower SGR than the control group (P <0.05), but there was no significant difference in FE at this level (P >0.05). The activities of digestive enzymes and apparent digestibility coefficients of dry matter, protein, lipid and phosphorus significantly decreased with increasing dietary CM level. A similar trend was observed in the immune response where lysozyme activity significantly decreased compared with the control group when the substitution level was more than 20%. Results of the present study indicated that protein from CM could substitute less than 20% for fish meal protein without influencing the growth of Japanese seabass. The higher substitution levels of CM induced negative influences on growth, survival and serum lysozyme of Japanese seabass. [Copyright &y& Elsevier]

Stomach contents of 1603 small yellow croaker Pseudosciaena polyactis, sampled from seasonal bottom trawl surveys in the central Yellow Sea between March 2001 and January 2002, were examined. The results showed that small yellow croaker was a carnivorous predator and >30 prey species were identified from stomach contents analysis. Crustaceans (mainly euphausiids and decapods) were the most important prey, occurring in 93·1% of the stomachs containing food, and accounting for 77·6% of the total food by mass. Feeding activity was highest in autumn and lowest in spring and winter. Decapods were more important in summer, whereas euphausiids were more important during other seasons. Ontogenetic differences were found in the diet composition and feeding activity within the range of size (standard length, LS) studied. The importance of fishes and decapods increased with LS, whereas euphausiids, copepods and amphipods decreased in importance with LS. Dietary breadth increased markedly for adults. A positive relationship was found between LS and prey size. In each season the maximum diel feeding activity occurred at 0800 and 2400 hours, indicating that there was crepuscular and nocturnal feeding by small yellow croaker. [ABSTRACT FROM AUTHOR]

The digestion, absorption and post absorptive metabolism of a radiolabelled triacylglycerol (TAG; triolein) and a free fatty acid (FFA; oleic acid), delivered by tube feeding, was studied in herring Clupea harengus larvae, using metabolic chambers and video analysis. In general, a large amount of the delivered lipid was evacuated. Most of the evacuation occurred between 2 and 6 h after tube feeding although a group of larvae responded by rapidly evacuating the lipid (>50% before 2 h). The volume of the tube-fed lipid affected its utilization. A small volume of triolein (9·2 nl, representing c. 6% of gut filling capacity) resulted in a lower proportion of fast evacuating larvae and improved utilization (lower evacuation and higher absorption: body incorporation and catabolism) compared with 50·6 nl ( c. 17% of gut filling capacity). Increases in the volume of tube fed triolein enhanced only marginally label absorption and led to a steep rise in evacuation. At a comparable high volume (50·6 nl), oleic acid, which does not require digestion, was better absorbed and less evacuated than triolein. The video observation of the lipid digestive process revealed a considerable gut contractile activity that appeared effective in processing the tube fed lipid. Also, the gut wall seemed very sensitive to physical pressure. Signs of chemical degradation during lipid digestion were also noted. The metabolic studies, together with video image analysis, suggested that the limiting step for the utilization of high dietary lipid levels may have been the lipid absorption into the enterocytes and transport into the body, rather than lipid digestion. The results support the notion that the rate of lipid digestion and absorption in fishes is slower than that of mammals. [ABSTRACT FROM AUTHOR]