Freshwater fish biodiversity restoration in floodplain rivers requires connectivity and habitat heterogeneity at multiple spatial scales.

With a sixth mass extinction looming and freshwater biodiversity declining at unprecedented rates, evaluating ecological efficacy of river restoration efforts is critical in combatting global biodiversity loss. Here, we present a comprehensive study of the functioning for fishes of 46 river restoration projects in the river Rhine, one of the world's most heavily engineered lowland rivers. Floodplains with permanent, either one- or two-sided lateral connectivity to the main channel, favour total fish abundance, and are essential as nursery areas for riverine fishes. Habitat heterogeneity had a strong positive effect on species richness but was negatively related with fish abundances. However, the effects of environmental variables varied between ecological groups and spatial scales. Surprisingly, richness of critical rheophilic fishes declined with large-scale habitat heterogeneity (~1000 m), while it increased at small scales (~100 m), possibly because of the presence of unfavourable habitats for this ecological group at larger scales. Clearly, there is no one-size-fits-all design for river restoration projects. Whether a river section is free-flowing or impounded dictates the scope and efficacy of restoration projects and, within a river section, multiple complementary restoration projects might be key to mitigate freshwater fish biodiversity loss. An essential element for success is that these projects should retain permanent lateral connection to the main channel.

30 years of large river restoration: How long do restored floodplain channels remain suitable for targeted rheophilic fishes in the lower river Rhine?

The ecological efficacy of river restoration projects may change over time, resulting in the loss of their ecological function for targeted species. The goal of this study was to evaluate the rheophilic nursery function of restored floodplain channels over time, by analysing 30 years of monitoring data from 12 restoration projects in the lower river Rhine. We hypothesised that the nursery function would change over time, caused by the combined effects of decreasing flow conditions and succession processes affecting habitat heterogeneity. We found that nursery area suitability for rheophilic fish was almost 4 times higher in two-sided connected channels than in one-sided connected channels, although the response trends of rheophilic fish were similar for both water body types. These response curves showed clear optima with channel age, for rheophilic fish abundance at 13 to 14 years post-restoration, indicating optimal nursery conditions. On the other hand, rheophilic species richness showed a steadily decreasing trend with channel age, suggesting aging channels became less suitable as nursery areas for most rheophilic fish species. The presence of permanent flow was found to be the main driving factor in explaining both rheophilic fish community trends and habitat succession in individual restored channels. We did not observe an effect of habitat heterogeneity on nursery function for rheophilic fish. To create and maintain optimal nursery conditions in restored floodplain channels of strongly anthropogenically influenced rivers such as the river Rhine, we propose a management strategy involving cyclic rejuvenation through human intervention, focusing on restoring permanent flow, with a frequency of on average every 15 years, depending on the rate of aggradation and targeted rheophilic species. We also propose a thorough investigation of the relationship between habitat heterogeneity and nursery success in floodplain channels, as a next step in the identification of suitable nursery areas for rheophilic fishes.

Integration of Algae to Improve Nitrogenous Waste Management in Recirculating Aquaculture Systems: A Review.

This review investigates the performance and the feasibility of the integration of an algal reactor in recirculating aquaculture systems (RAS). The number of studies related to this topic is limited, despite the apparent benefit of algae that can assimilate part of the inorganic waste in RAS. We identified two major challenges related to algal integration in RAS: first, the practical feasibility for improving nitrogen removal performance by algae in RAS; second, the economic feasibility of integrating an algal reactor in RAS. The main factors that determine high algal nitrogen removal rates are light and hydraulic retention time (HRT). Besides these factors, nitrogen-loading rates and RAS configuration could be important to ensure algal performance in nitrogen removal. Since nitrogen removal rate by algae is determined by HRT, this will affect the size (area or volume) of the algal reactor due to the time required for nutrient uptake by algae and large surface area needed to capture enough light. Constraints related to design, space, light capture, and reactor management could incur additional cost for aquaculture production. However, the increased purification of RAS wastewater could reduce the cost of water discharge in places where this is subject to levees. We believe that an improved understanding of how to manage the algal reactor and technological advancement of culturing algae, such as improved algal reactor design and low-cost artificial light, will increase the practical and economic feasibility of algal integration in RAS, thus improving the potential of mass cultivation of algae in RAS.

Transmission of white spot syndrome virus (WSSV) from Dendronereis spp. (Peters) (Nereididae) to penaeid shrimp.

Dendronereis spp. (Peters) (Nereididae) is a common polychaete in shrimp ponds built on intertidal land and is natural food for shrimp in traditionally managed ponds in Indonesia. White spot syndrome virus (WSSV), an important viral pathogen of the shrimp, can replicate in this polychaete (Desrina et al. 2013); therefore, it is a potential propagative vector for virus transmission. The major aim of this study was to determine whether WSSV can be transmitted from naturally infected Dendronereis spp. to specific pathogen-free (SPF) Pacific white shrimp Litopenaeus vannamei (Boone) through feeding. WSSV was detected in naturally infected Dendronereis spp. and Penaeus monodon Fabricius from a traditional shrimp pond, and the positive animals were used in the current experiment. WSSV-infected Dendronereis spp. and P. monodon in a pond had a point prevalence of 90% and 80%, respectively, as measured by PCR. WSSV was detected in the head, gills, blood and mid-body of Dendronereis spp. WSSV from naturally infected Dendronereis spp was transmitted to SPF L. vannamei and subsequently from this shrimp to new naïve-SPF L. vannamei to cause transient infection. Our findings support the contention that Dendronereis spp, upon feeding, can be a source of WSSV infection of shrimp in ponds.

Horizontal transmission dynamics of White spot syndrome virus by cohabitation trials in juvenile Penaeus monodon and P. vannamei.

White spot syndrome virus (WSSV), a rod-shaped double-stranded DNA virus, is an infectious agent causing fatal disease in shrimp farming around the globe. Within shrimp populations WSSV is transmitted very fast, however, the modes and dynamics of transmission of this virus are not well understood. In the current study the dynamics of disease transmission of WSSV were investigated in small, closed populations of Penaeus monodon and Penaeus vannamei. Pair cohabitation experiments using PCR as a readout for virus infection were used to estimate transmission parameters for WSSV in these two species. The mortality rate of contact-infected shrimp in P. monodon was higher than the rate in P. vannamei. The transmission rate parameters for WSSV were not different between the two species. The relative contribution of direct and indirect transmission rates of WSSV differed between the two species. For P. vannamei the direct contact transmission rate of WSSV was significantly lower than the indirect environmental transmission rate, but for P. monodon, the opposite was found. The reproduction ratio R0 for WSSV for these two species of shrimp was estimated to be above one: 2.07 (95%CI 1.53, 2.79) for P. monodon and 1.51 (95%CI 1.12, 2.03) for P. vannamei. The difference in R0 between the two species is due to a lower host mortality and hence a longer infectious period of WSSV in P. monodon.

Transmission of fish-borne zoonotic trematodes (Heterophyidae) to common carp (Cyprinus carpio) is independent of density of fish and trematodes.

Fish-borne zoonotic trematodes (FZTs) can cause major human health problems. The aim of this study was to quantify the transmission of parapleurolophocercous cercariae to common carp (Cyprinus carpio) and to study the effect of the density of cercariae and the density of fish on transmission with respect to the volume of water and surface area of the bottom. Fish were kept individually either as controls (n= 91) or were exposed to 250 cercariae in tubes with a volume of 25, 50, 100, 250 or 500 ml water (n= 190) with a surface area of 4, 12, 21, 30 or 49 cm2 (n= 195). The dose to which the fish were exposed was kept constant. Infection occurred in 94-100% of fish, with a mean of 15-18 metacercariae per fish and the proportion of FZTs established at 0.06-0.07 metacercariae per cercariae per fish. Neither the prevalence of infection with FZTs nor the number of metacercariae per fish nor the proportion of FZTs established were significantly associated with differences in the density of cercariae or the density of fish per ml water or per cm2 surface area. Thus, it was concluded that the transmission of cercariae to fish is independent of density.

Dietary electrolyte balance affects the nutrient digestibility and maintenance energy expenditure of Nile tilapia.

Acid-base disturbances caused by environmental factors and physiological events including feeding have been well documented in several fish species, but little is known about the impact of dietary electrolyte balance (dEB). In the present study, we investigated the effect of feeding diets differing in dEB (-100, 200, 500 or 800 mEq/kg diet) on the growth, nutrient digestibility and energy balance of Nile tilapia. After 5 weeks on the test diet, the growth of the fish was linearly affected by the dEB levels (P< 0·001), with the lowest growth being observed in the fish fed the 800 dEB diet. The apparent digestibility coefficient (ADC) of fat was unaffected by dEB, whereas the ADC of DM and protein were curvilinearly related to the dEB levels, being lowest and highest in the 200 and 800 dEB diets, respectively. Stomach chyme pH at 3 h after feeding was linearly related to the dEB levels (P< 0·05). At the same time, blood pH of the heart (P< 0·05) and caudal vein (P< 0·01) was curvilinearly related to the dEB levels, suggesting the influence of dEB on postprandial metabolic alkalosis. Consequently, maintenance energy expenditure (MEm) was curvilinearly related to the dEB levels (P< 0·001), being 54 % higher in the 800 dEB group (88 kJ/kg(0·8) per d) than in the 200 dEB group (57 kJ/kg(0·8) per d). These results suggest that varying dEB levels in a diet have both positive and negative effects on fish. On the one hand, they improve nutrient digestibility; on the other hand, they challenge the acid-base homeostasis (pH) of fish, causing an increase in MEm, and thereby reduce the energy required for growth.

Replication of white spot syndrome virus (WSSV) in the polychaete Dendronereis spp.

This study investigated whether WSSV replicates in naturally infected Dendronereis spp., a common polychaete (Nereididae) species in shrimp ponds in Indonesia. To detect WSSV replication, (i) immunohistochemistry (IHC) using a monoclonal antibody against WSSV VP28 protein and (ii) nested RT-PCR using specific primers set for the vp28 gene to detect WSSV-specific mRNA were applied. WSSV immunoreactive-nuclei were detected in the gut epithelium of the polychaete and WSSV mRNA was detected with nested RT-PCR. This, together with the IHC results, confirmed that WSSV could replicate in Dendronereis spp. This is the first report showing that WSSV replicated in a naturally infected non-crustacean host.

Control of voluntary feed intake in fish: a role for dietary oxygen demand in Nile tilapia (Oreochromis niloticus) fed diets with different macronutrient profiles.

It has been hypothesised that, at non-limiting water oxygen conditions, voluntary feed intake (FI) in fish is limited by the maximal physiological capacity of oxygen use (i.e. an 'oxystatic control of FI in fish'). This implies that fish will adjust FI when fed diets differing in oxygen demand, resulting in identical oxygen consumption. Therefore, FI, digestible energy (DE) intake, energy balance and oxygen consumption were monitored at non-limiting water oxygen conditions in Nile tilapia fed diets with contrasting macronutrient composition. Diets were formulated in a 2 × 2 factorial design in order to create contrasts in oxygen demand: two ratios of digestible protein (DP):DE ('high' v. 'low'); and a contrast in the type of non-protein energy source ('starch' v. 'fat'). Triplicate groups of tilapia were fed each diet twice daily to satiation for 48 d. FI (g DM/kg(0·8) per d) was significantly lower (9·5%) in tilapia fed the starch diets relative to the fat diets. The DP:DE ratio affected DE intakes (P < 0·05), being 11% lower with 'high' than with 'low' DP:DE ratio diets, which was in line with the 11·9% higher oxygen demand of these diets. Indeed, DE intakes of fish showed an inverse linear relationship with dietary oxygen demand (DOD; R 2 0·81, P < 0·001). As hypothesised ('oxystatic' theory), oxygen consumption of fish was identical among three out of the four diets. Altogether, these results demonstrate the involvement of metabolic oxygen use and DOD in the control of FI in tilapia.

Dietary nutrient composition affects digestible energy utilisation for growth: a study on Nile tilapia (Oreochromis niloticus) and a literature comparison across fish species.

The effect of the type of non-protein energy (NPE) on energy utilisation in Nile tilapia was studied, focusing on digestible energy utilisation for growth (k(gDE)). Furthermore, literature data on k(gDE) across fish species were analysed in order to evaluate the effect of dietary macronutrient composition. A total of twelve groups of fish were assigned in a 2 × 2 factorial design: two diets ('fat' v. 'starch') and two feeding levels ('low' v. 'high'). In the 'fat'-diet, 125 g fish oil and in the 'starch'-diet 300 g maize starch were added to 875 g of an identical basal mixture. Fish were fed restrictively one of two ration levels ('low' or 'high') for estimating k(gDE). Nutrient digestibility, N and energy balances were measured. For estimating k(gDE), data of the present study were combined with previous data of Nile tilapia fed similar diets to satiation. The type of NPE affected k(gDE) (0.561 and 0.663 with the 'starch' and 'fat'-diets, respectively; P < 0.001). Across fish species, literature values of k(gDE) range from 0.31 to 0.82. Variability in k(gDE) was related to dietary macronutrient composition, the trophic level of the fish species and the composition of growth (fat:protein gain ratio). The across-species comparison suggested that the relationships of k(gDE) with trophic level and with growth composition were predominantly induced by dietary macronutrient composition. Reported k(gDE) values increased linearly with increasing dietary fat content and decreasing dietary carbohydrate content. In contrast, k(gDE) related curvilinearly to dietary crude protein content. In conclusion, energy utilisation for growth is influenced by dietary macronutrient composition.

Coping strategies in farmed African catfish Clarias gariepinus. Does it affect their welfare?

The objective of this study was to assess whether and how coping strategies affect the welfare of African catfish Clarias gariepinus housed at low and high densities. Group composition influenced feed intake; re-active groups (comprised of 100% re-active fish) had a lower specific growth rate (G) and feed intake and a higher feed conversion ratio (R(FC)) than pro-active groups. Furthermore, re-active groups had a lower energy retention than pro-active groups. The latter was fully due to differences in feed intake, since energy partitioning (on % total gross energy intake basis) was similar among the group composition treatments. Fish held at high stocking density showed a higher R(FC) and feeding speed and a lower energy retention and agonistic behaviour. None of the measured variables was influenced by the interaction effect. In mixed groups, G and number of skin lesions seemed to be affected by different behavioural phenotypes at low stocking density, but not at high density. These results indicate that both stocking density and group composition affect physical and behavioural responses of C. gariepinus. Furthermore, physical and behavioural data of individual fish housed in mixed groups suggest that coping strategy affects the fitness of different behavioural phenotypes at low, but not at high, stocking density.

Time-related changes of the intestinal morphology of Atlantic salmon, Salmo salar L., at two different soybean meal inclusion levels.

Abstract Soybean meal (SBM) induces enteritis in the distal intestine of Atlantic salmon. The present study assesses the effects of SBM concentrations on the kinetics of the enteritis process. Fish of 300 g, kept at 12 degrees C, were fed diets with different SBM inclusions: 0%, 10% and 20% SBM for 57 days. Samples of the distal intestine of five fish per treatment were taken for histological and electron microscopical analysis. A semi-quantitative scoring system was used to assess the degree of the morphological changes induced by SBM feeding in the distal intestinal epithelium. The first signs of enteritis appeared earlier in the salmon fed the 20SBM diet than in those fed the 10SBM diet. Thereafter, the condition increased steadily, displaying no signs of recovery. Furthermore, at the lower concentration, the process marking the onset of enteritis began more gradually than at the higher concentration and it displayed a tendency to stabilize after 13-20 days of continuous feeding. Electron microscopy indicated that the endocytosis process was hampered at day 3 of 20SBM and at 7 days of 10SBM. Furthermore, a strong reduction of microvilli was already evident after 7 days of 20SBM feeding, thus indicating a decreased uptake capacity of the distal enterocytes. In addition, transformation and migration of eosinophilic granulocytes was observed, which, in combination with the lysozyme C immunoreactivity supports their protective role during the inflammatory process in the distal gut of Atlantic salmon. It can be concluded that the severity of enteritis and its kinetics are concentration-dependent, showing no signs of recovery during feeding with diets containing SBM.

Kinetics of Lactobacillus plantarum 44a in the faeces of tilapia (Oreochromis niloticus) after its intake in feed.

AIMS: To study the kinetic passage of Lactobacillus plantarum 44a from feed to faeces of tilapia in order to calculate the number of Lactobacillus excreted. METHODS AND RESULTS: In a single-dose experiment, duplicate lots of 26 fish devoid of intestinal lactobacilli were fed with diets containing c. 4.5 x 10(11), 6.3 x 10(8), 6.0 x 10(5) and 0 CFU of Lact. plantarum 44a per single feed ration. In the multiple-dose experiment, duplicate lots of 30 fish each were supplied with a diet containing 1 x l0(11) CFU of Lact. plantarum 44a as follows: 14 times in 14 days, five times in 14 days, once in 14 days and zero times in 14 days. Faeces were periodically collected and analysed for their lactobacilli content by using a selective media. The kinetics of Lactobacillus in the faeces was described as a pulse signal defined by three parameters: theta, A(o) and the time. theta, was identified as the time to reach the peak (x axis) and A(o) was a constant. A(o) divided by e, was identified as the height of the peak (y axis). The area below the curve A(o)theta allowed the calculation of the total number of lactobacilli excreted. The ability of the mathematical model to describe the actual values was tested by a linear regression analysis. In most of the cases, the equations showed an intercept close to zero (P > 0.05) and angular coefficients near one. CONCLUSIONS: Lactobacillus plantarum 44a was excreted in short pulse signals described by a mathematical model which allowed calculating the area below the curve and consequently the survival rate. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides a quantitative method to study the kinetics of excretion of a probiotic bacterium in the faeces.

Soybean meal induces intestinal inflammation in common carp (Cyprinus carpio L.).

The development of soybean meal (SBM) induced enteritis in the hindgut of the omnivorous common carp (Cyprinus carpio L.). The developed condition was assessed when carp, continuously fed on animal protein, were transferred to a diet in which 20% of the protein was replaced by SBM. After week 1, most of the inflammation parameters were already present, but at week 3, a strong aggravation of the condition was observed which included a shortening of the mucosal folds, the disappearance of the supranuclear vacuoles, an increased number of goblet cells, a thickened lamina propria and sub-epithelial mucosa with increased numbers of basophilic granulocytes as well as a decreased uptake capacity of enterocytes (impaired endocytosis and microvilli). Contrary to previous observations made with respect to Atlantic salmon, common carp start to recover from the fourth to the fifth week after switching to SBM feeding. At this stage, the supranuclear vacuoles refill and most of the parameters revert to basal levels. During the enteritis process, a real-time quantitative PCR analysis was conducted to measure the expression of inflammatory and anti-inflammatory cytokine genes in the isolated intraepithelial lymphocytes (IEL). The pro-inflammatory interleukin 1 beta (IL-1 beta) and tumour necrosis factor alpha1 (TNF-alpha1) genes were up-regulated during the inflammation process while the anti-inflammatory interleukin 10 (IL-10) was down-regulated after an initial up-regulation at week 1. Transforming growth factor beta (TGF-beta) expression showed an up-regulation from week 3 onwards despite the high Ct value and the low primer efficiency shown. This study confirms the contribution of IEL (mainly T-like cells) and basophils in the enteritis process. In addition, the results show a clear involvement of up- and down-regulated cytokine genes in both the onset and recovery of the SBM-induced enteritis in the hindgut of carp.

Tropical agricultural residues and their potential uses in fish feeds: the Costa Rican situation.

In Costa Rica as many other tropical countries, the disposal problem of agricultural wastes is widely recognized but efforts to find solutions are not equal for different sectors. This study describes the situation of major agricultural residues in Costa Rica, identifying the activities with higher amounts produced and, the potential use of these residues in fish feeds. In Costa Rica, during the 1993-1994 production season, major agricultural sectors (crop and livestock) generated a total amount of 3.15-3.25 million MT of residues (classified in by-products: used residues and wastes: not used residues). Some residues are treated to turn them into valuable items or to diminish their polluting effects (e.g., the so-called by-products). About 1.56-1.63 million MT of by-products were used for different purposes (e.g. fertilization, animal feeding, fuel, substrates in greenhouses). However, the remainder (1.59-1.62 million MT) was discharged into environment causing pollution. About 1.07-1.2 million MT wastes came from major crop systems (banana, coffee, sugarcane and oil palm) whereas the remainder came from animal production systems (porcine and poultry production, slaughtering). These data are further compared to residues estimates for the 2001-2002 production season coming from the biggest crops activities. Unfortunately, most of the studied wastes contain high levels of moisture and low levels of protein, and also contain variable amounts of antinutritional factors (e.g., polyphenols, tannins, caffeine), high fibre levels and some toxic substances and pesticides. All these reasons may limit the use of these agricultural wastes for animal feeding, especially in fish feeds. The potential use of the major vegetable and animal residues in fish feeds is discussed based on their nutritional composition, on their amount available over the year and on their pollution risks. Other constraints to use these wastes in fish feeds are the extra costs of drying and, in most cases, of transportation from several dispersed locations. It was stated that most interesting wastes are rejected green banana and coffee pulp.

Biological treatments affect the chemical composition of coffee pulp.

Biological treatments were applied to fresh coffee pulp (CoP) to improve its nutritive value for monogastric animals by reducing its content of cellulose and antinutritional factors (ANFs) such as total phenols, tannins and caffeine. Treatments were: (1) ensiling with 0, 50 and 100 gkg(-1) molasses for 2 and 3 months, (2) aerobic decomposition for 0, 7, 14, 21, 28, 35 and 42 days, (3) aerobic bacterial inoculation (Bacillus sp.) for 0, 7, 14, 21 and 28 days. Ensiled CoP (E-CoP) showed higher fat and ash contents than oven-dried-CoP (OD-CoP; P<0.05). Similarly, true protein values tended to increase. The cellulose and total phenols levels of E-CoP were lower than OD-CoP (P<0.05). The E-CoP tannins levels tended to be lower than OD-CoP whereas caffeine levels remained unaffected. Improvement in the nutritional quality of E-CoP was associated with higher fat and protein contents and reduction of cellulose, total phenols and tannins. The aerobic decomposition treatment improved the nutritional quality of CoP by increasing true protein and fat contents. In addition, total phenols, tannins, caffeine and cellulose contents were reduced by an increase in treatment time (P<0.05). Bacterial treatment increased the protein content of CoP after 21 days (from 137 to 392 gkg(-1)) and decreased it after 28 days. Cellulose, total phenols, tannins and caffeine contents reduced with an increase in time of bacterial degradation. Bacterial treatment improved the CoP quality by increasing protein content and reducing cellulose and ANFs, especially after 21 days of treatment. Both the aerobic decomposition (after 21-28 days) and the aerobic bacterial degradation of CoP (after 21 days) appeared more suitable to improve the nutritional quality of CoP than the ensiling.

Changes in oxygen content and acid-base balance in arterial and portal blood in response to the dietary electrolyte balance in pigs during a 9-h period after a meal.

The effect of two dietary electrolyte balance (dEB, Na+ + K+ - Cl-) levels on arterial and portal blood oxygen content, blood pH, and acid-base status in pigs was studied during a 9-h period after a meal, using a crossover experimental design. The dEB levels were established by changing the Cl- level in the diets. Four pigs with a mean weight of 45 kg were surgically fitted with catheters in the carotid artery and portal vein. Two dEB levels (-100 and 200 mEq/kg) were evaluated in two periods of 1 wk each. Feed was given at 2.6 times the maintenance requirement for energy in two meals per day. Water was freely available. Blood samples were taken at 0, 0.5, 1, 1.5, 2, 3, 4, 6, and 9 h after feeding. Blood hemoglobin; O2 pressure; O2 saturation; O2 content; pH; PCO2; HCO3-; base excess; and Na+, K+, and Cl- contents were measured. Oxygen contents in arterial and portal blood were lower (P < 0.008) in the -100 mEq/kg group (5.78 and 4.82 mmol/L respectively) compared to the 200 mEq/kg group (6.18 and 4.99 mmol/L respectively). This was related to the lower hemoglobin content in the blood of animals in the -100 mEq/kg group. Arterial and portal blood pH were lower (P < 0.003) at -100 mEq/kg (7.46 and 7.37) than at 200 mEq/kg (7.49 and 7.43). The difference in blood pH between the two groups was sustained throughout the sampling period. The average values of arterial and portal blood for base excess and HCO3- content were higher (P < 0.001) at high dEB (6.96 and 31.0 mmol/L, respectively, for -100 mEq/kg and 12.54 and 35.9 mmol/ L, respectively, for 200 mEq/kg). The Na+ concentration in the blood was increased and K+ and Cl- concentrations were decreased (P < 0.02) by increasing dEB from -100 mEq/kg to 200 mEq/kg. Blood electrolyte balance level was higher (P < 0.001) in the 200 mEq/kg dEB group than in the -100 mEq/kg dEB group. In conclusion, dEB changed blood oxygen content and pH, and influenced the acid-base buffer system in pigs. Also, within each group, pigs maintained a relatively constant blood pH level during the 9-h period after feeding.

Changes in fatty acid concentrations in tissues of African catfish, Clarias gariepinus Burchell, as a consequence of dietary carnitine, fat and lysine supplementation.

A study was undertaken to examine the effect of different dietary carnitine (200 and 1000 mg/kg diet) and fat (90 and 190 g/kg diet) supplementation on growth and fatty acid concentrations of fish fed either with a low- (13 g/kg) or a high-lysine (21 g/kg) diet. African catfish (22.7 g/fish), Clarias gariepinus Burchell, juveniles were stocked (sixteen aquaria, twenty-five fish per aquarium) and fed for a maximum of 74 d. Dietary lysine had a clear effect on growth performance and feed conversion ratios, but dietary carnitine supplements had no effect. High-carnitine supplements increased total carnitine content (P<0.0004) and reduced tissue free carnitine: acyl-carnitine ratio (P<0.05) compared with low-carnitine supplements. High-fat supplements decreased liver carnitine concentrations. Clear effects on liver fatty acid concentrations were observed in high-carnitine-fed fish compared with low-carnitine-fed fish. The primary liver fatty acids affected were n-6 (linoleic acid), n-3 (eicosapentanoic acid) and n-3 (docosahexanoic acid). The whole-body fatty acid balance suggested that n-3 disappeared (apparently by beta-oxidation) more readily than n-6 and/or n-3. From 774 mg n-3 eaten by high-lysine-high-fat-low-carnitine fish, 58 % was not assimilated into body tissues. High-carnitine-fed fish showed an increase in n-3 oxidation by 7 % compared with low-carnitine fish. Although dietary carnitine did not improve body growth, these results support the hypothesis that carnitine can enhance the mobilisation of long-chain fatty acids towards oxidation.

Feed intake, growth, digestibility of dry matter and nitrogen in young pigs as affected by dietary cation-anion difference and supplementation of xylanase.

An experiment was conducted to test the effect of dietary cation-anion difference (CAD, Na(+) + K(+)-Cl(-), mEq/kg diet) and xylanase addition on feed consumption, digestibility of nutrients, plasma electrolyte balance and growth performance in young pigs. A 2 x 3 factorial arrangement with three dietary CAD levels (-100, 200, and 500 mEq/kg) and two levels of xylanase supplementation (0 and 0.1% xylanase derived from Trichoderma longibrachiatum) was used. Thirty-six individually housed, castrated pigs (5 weeks old) with an initial body weight of 9.34 +/- 0.28 kg (mean +/- SEM) were randomly assigned to the six treatments. Diets were provided to pigs as cold pellets. Pigs had ad libitum access to feed and water. Venous plasma Cl(-) concentration was higher (p < 0.0001) in dietary CAD of - 100 mEq/kg group compared with the other two CAD groups. Dietary CAD did not affect Na(+) and K(+) concentrations in the venous plasma. Growth rates were higher (p < 0.05) in pigs receiving dietary CAD of 200 mEq/kg (657 g/pig.day) and dietary CAD of 500 mEq/kg (603 g/pig.day) than in pigs receiving dietary CAD of -100 mEq/kg (484 g/pig.day). Faecal dry matter and nitrogen decreased with increasing dietary CAD. Faecal apparent digestibility of dry matter and nitrogen was higher (p < 0.05) in the dietary CAD of 500 mEq/kg compared to the two lower level CAD groups. Supplementation of xylanase did not affect the performance of pigs. Xylanase addition in the diet significantly increased apparent faecal digestibility of dry matter and tended to increase apparent digestibility of nitrogen. No interaction between dietary CAD and xylanase was found. In conclusion, dietary CAD influenced the performance and digestibility of nutrients of pigs. Xylanase supplementation improved digestibility of dry matter.

Pathways for urea production during early life of an air-breathing teleost, the African catfish Clarias gariepinus Burchell.

Embryos and larvae of the African catfish Clarias gariepinus excrete significant quantities of urea. The present study focused on the potential urea-generating pathways during early development of this teleost; uricolysis, argininolysis and the ornithine-urea cycle (OUC). Uricase, allantoinase, allantoicase and ureidoglycollate lyase of the uricolytic pathway were expressed in all early life stages and in adult liver of C. gariepinus. Uricase activity increased in starved larvae compared with yolk-sac larvae. The key regulatory enzyme of the teleost OUC, carbamoyl phosphate synthetase III (CPSase III), was expressed predominantly in muscle of developing C. gariepinus larvae and showed negligible activity in the absence of its allosteric effector N-acetyl-L-glutamate. CPSase III and ornithine carbamoyl transferase activities increased in fed larvae compared with starved larvae. In contrast to the early developmental stages, adult C. gariepinus expressed only low and variable levels of CPSase III, suggesting that, under the experimental conditions employed, OUC expression is influenced by developmental stage in this species. The data indicate that early C. gariepinus life stages express the enzymes necessary for urea production by uricolysis, argininolysis and the OUC, and this may explain why urea tissue levels and urea excretion rates are substantial during the early development of this air-breathing teleost.