A Leopard Seal from Hout Bay,South Africa

The catch per unit effort of Oreochromis mossambicus, Clarias gariepinus and Cyprinus carpio at different localities at Hartbeespoort Dam was investigated. Catches of the three species were between three and ten times higher on the southern shore of the lake than on the northern shore. The gradient of each locality was found to be the most important variable determining catch. Gill-net catches of O. mossambicus from littoral and limnetic stations indicated equal abundance of the species in these two habitats. The implications of the results for improved predictions of fish yield from lakes, and for management are discussed.     

Invasive alien freshwater fishes in the Wilderness Lakes System,a wetland of international importance in the Western Cape Province,South Africa

The Wilderness Lakes System incorporates a RAMSAR listed wetland. Previous ichthyological surveys reported three invasive freshwater fishes; Oreochromis mossambicus (Mozambique tilapia), Gambusia affinis (mosquitofish) and Micropterus salmoides (largemouth bass) from this system. To assess the status of these alien fishes, the fish assemblages in the lakes system were sampled with seine nets and fyke nets in 2009 and 2010. A total of 87 893 fish comprising 16 species were caught. In addition to confirming the persistence of O. mossambicus and G. affinis in the system, the current study also reports the presence of a new invader, Cyprinus carpio (common carp). M. salmoides were absent from 2009 and 2010 samples.     

Dietary Supplementation with Allspice Pimenta dioica Reduces the Occurrence of Streptococcal Disease during First Feeding of Mozambique Tilapia Fry

Abstract

Allspice Pimenta dioica as a feed additive was studied for its effects on growth performance and disease resistance in Mozambique Tilapia Oreochromis mossambicus. Five isonitrogenous (36% crude protein) and isocaloric (18.5 kJ/g) diets were formulated to contain 0 (control), 5, 10, 15, or 20 g of allspice/kg of fish feed. In a 50-d feeding trial, 15 plastic tanks (21 L) were stocked with 35 fish fry (0.012 g) each. After the feeding trial, fish were exposed to Streptococcus iniae and mortalities were recorded. The second-order polynomial regression indicated that the dietary allspice level of 10 g/kg provided the best growth performance and feed utilization. The greatest survival after pathogen challenge was also obtained from the diet supplemented with allspice at 10 g/kg. Therefore, allspice acts as a growth promoter to improve feed utilization and weight gain in Mozambique Tilapia fry and acts an antimicrobial agent to enhance disease resistance during first feeding of fry. These results suggest that allspice can be used as an alternative to antibiotics in controlling streptococcal disease in tilapia culture.

Received October 19, 2012; accepted January 20, 2014     

Effect of Low Dietary Magnesium on Immune Response and Osmoregulation of Atlantic Salmon

Abstract

The influences of dietary magnesium on immune response and on osmoregulation in parr of Atlantic salmon Salmo salar were determined. Groups of fish were fed a casein–gelatin diet unsupplemented (containing about 200 mg Mg/kg) or supplemented with either 300 or 500 mg Mg/kg dry diet (as MgSO₄) for 12 weeks before vaccination to produce fish with different Mg levels, and the feeding regime was continued throughout the study. No differences were observed between the treatment groups in serum-specific antibody levels every second week for 8 weeks after vaccination against Vibrio anguillarum serotypes O1 and O2. Both lysozyme levels and spontaneous hemolytic activities in serum were elevated in vaccinated fish compared with unvaccinated fish. Neither lysozyme activity, complement hemolytic activity, total protein in serum nor blood hemoglobin were affected by dietary Mg. The spontaneous hemolytic activity in serum was lower in fish fed the unsupplemented diet and highest in fish fed the diet supplemented with 500 mg Mg/kg. After 28 weeks on the diets supplemented with graded levels of Mg, a salinity tolerance test (32.5 g/L, 24 h) was performed. High mortality and elevated serum chloride concentrations in all groups after 24 h reflected a general salinity intolerance, but the highest serum chloride level was observed in fish fed the unsupplemented diet. This indicates that low dietary Mg affects the osmoregulation of Atlantic salmon.     

The anaesthetic potency of benzocaine-hydrochloride in three freshwater fish species

Anaesthesia was induced in the common carp, Cyprinus carpio, tiiapia, Oreochromis mossambicus and rainbow trout, Salmo gairdneri, at concentrations of 25; 50; 75 and 100 mg/1 of benzocaine-hydrochloride as well as neutralized benzocaine-hydrochloride at water temperatures of 15; 20 and 25 °C. The results obtained indicated intra-and interspecific differences in the susceptibility of fish to anaesthesia due to metabolic, chemoreceptive and temperature tolerance differences in and amongst the three species.     

Diet of the cyprinid fish Barbus aeneus (Burchell) in the P.K. le Roux Dam,South Africa,with special reference to the effect of turbidity on zooplanktivory

Barbus aeneus is one of the most important fishes in the P.K. le Roux Dam, being found over the whole surface and on the bottom down to the thermocline or to 30 m. It is omnivorous, but its diet varies with size. Below a length of 100 mm it feeds mainly on zoobenthos, from 101-300 mm zooplankton is the principal food but in larger fish vegetable food becomes increasingly important. B. aeneus is the principal vertebrate consumer of zooplankton in the dam, but takes only the larger species which are located visually. The quantity of zooplankton in the diet was related, not to its density, but to light and transparency which were the most important non-seasonal influences on the diet. Seasonal effects were marked, zooplankton being most important during summer and autumn while empty stomachs were most frequent in winter and spring. In rivers, larger B. aeneus feed on bigger invertebrates and on vegetable material. These are limited in the P.K. le Roux Dam and sub-adults experience high mortality once they can no longer feed efficiently on zooplankton. The size at which this occurs is determined largely by turbidity, and this should be taken into consideration in formulating management policies.     

A short note on how tied fights affect cortisol levels

Previous work exploring the interrelationships between sex steroids (e.g. androgens, testosterones and 11‐ketotestosterones) and social behavior in teleosts suggest that mirror‐elicited aggression in cichlid fish may not trigger a hormonal response. Using the Mozambique tilapia (Oreochromis mossambicus) to analyze immune responses as a result of social stress, we measured levels of cortisol and melatonin using Enzyme‐Linked Immunosorbent Assay (ELISA) assays. In this work, we demonstrated that cortisol concentrations are significantly lower yet the levels of melatonin remain unchanged in tilapia that are fighting their mirror image. Our results suggested that in tied fights, certain hormone levels remain unchanged (e.g. androgens) due to the lack of melatonin induction.     

Evaluation of Emamectin Benzoate for the Control of Experimentally Induced Infestations of Argulus sp. in Goldfish and Koi Carp

Abstract

The effect of 0.2% emamectin benzoate (SLICE; Intervet/ Schering-Plough Animal Health, Roseland, New Jersey) administered in top-dressed, pelleted commercial fish feed was evaluated for control of freshwater Argulus sp. in goldfish Carassius auratus and koi carp, a variant of common carp Cyprinus carpio, in freshwater aquaria at 24–25°C. Sixteen individually housed goldfish were each exposed to 37 Argulus. The number of fish lice attached to each fish at the start of the experiment was not determined; however, the total number of motile fish lice in each aquarium (on fish and in the water) was determined at the start and end of each experiment. Eight goldfish were fed the control diet (0 μg · kg fish biomass^?1 · d^?1) and eight were fed the medicated diet (50 μg · kg fish biomass^?1 · d^?1) for seven consecutive days. After treatment, fish louse infestation in controls was 20.5 ± 1.5 (mean ± SE) lice per fish. No Argulus were found on fish in the treated group. In a separate experiment, 10 individually housed koi were each exposed to 128 Argulus. Five koi were fed the control diet and five were fed a low-dose medicated diet (5 μg · kg fish biomass^?1 · d^?1) for 7 d. After treatment, fish louse infestation among the controls was 14.6 ± 3.8 lice per koi. No Argulus were found on koi in the treated group. Hence, a 7-d regimen of oral emamectin benzoate controlled experimental infestation of Argulus when administered to goldfish at 50 μg · kg fish biomass^?1 · d^?1 and to koi at 5 μg · kg fish biomass^?1 · d^?1.

Received March 24, 2010; accepted January 17, 2011     

Prevalence of Francisella noatunensis subsp. orientalis in Cultured Tilapia on the Island of Oahu,Hawaii

Abstract

Francisellosis is an emergent disease in cultured and wild aquatic animals. The causative agent, Francisella noatunensis subsp. orientalis (Fno), is a gram-negative bacterium recognized as one of the most virulent pathogens of warmwater fish. The main objective of this project was to investigate the prevalence of Fno in cultured tilapia (specifically, Mozambique Tilapia Oreochromis mossambicus, Koilapia [also known as Wami Tilapia] O. hornorum, Blue Tilapia O. aureus, and Nile Tilapia O. niloticus hybrids) on the island of Oahu, Hawaii, using conventional and real-time PCR assays followed by statistical modeling to compare the different diagnostic methods and identify potential risk factors. During 2010 and 2012, 827 fish were collected from different geographical locations throughout the island of Oahu. Upon collection of fish, the water temperature in the rearing system and the length of individual fish were measured. Extraction of DNA from different tissues collected aseptically during necropsy served as a template for molecular diagnosis. High correlation between both molecular methods was observed. Moreover, the bacterium was isolated from infected tilapia on selective media and confirmed to be Fno utilizing a species-specific Taqman-based real-time PCR assay. Although a direct comparison of the prevalence of Fno between the different geographical areas was not possible, the results indicate a high prevalence of Fno DNA in cultured tilapia throughout the farm sites located on Oahu. Of the different tilapia species and hybrids currently cultured in Hawaii, Mozambique Tilapia were more susceptible to infection than Koilapia. Water temperature in the rearing systems and fish size also had a strong effect on the predicted level of infection, with fish held at lower temperatures and smaller fish being more susceptible to piscine francisellosis.

Received November 30, 2012; accepted February 22, 2013     

Pre-treatment of dietary plant feedstuffs with phytase and its effect on growth and mineral concentration in common carp (Cyprinus carpio L.)

Effect of phytase pre-treatment of dietary plant feed stuffs (PF) on growth and mineral concentration in common carp (C. carpio L.) was investigated. Diets used were: C0, diet with no supplement; CI, diet with incubated PF; CP0, diet supplemented with 3 g P/kg; CPI, diet with incubated PF supplemented with 3 g P/kg; Phyt0, diet fortified with 4000 U phytase/kg; PhytI, diet with PF incubated with 4000 U phytase/kg. Mean weight gain, SGR and FCR were the same (p < 0.05) in fish fed CP0, CPI or PhytI but less (p < 0.05) in other fish. Bone P was similar in fish fed CP0 (74.9), CPI (75.9) or PhytI (71.5 mg/g DM) but higher (p < 0.05) than in fish fed C0. Bone Ca and Mg were similar in fish fed CP0, CPI or PhytI but less (p < 0.05) in other fish. Bone Zn in fish fed C0, Phyt0 or PhytI was higher (p < 0.05) than that in fish fed CP0 or CPI. In conclusion, CP0, CPI and PhytI had the same effect, suggesting phytase pre-treatment as the most effective method. CPI did not have any advantage over CP0. Phytase increased mineral availability and utilization, which would minimize cost of mineral supplementation and discharges into the environment.     

Effect of housefly maggot meal (magmeal) diets on the performance, concentration of plasma glucose, cortisol and blood characteristics of Oreochromis niloticus fingerlings

A 56-day feeding trial was conducted to access the effect of housefly maggot meal (magmeal) diets on the performance, concentration of plasma glucose, cortisol and blood characteristics of Oreochromis niloticus fingerlings. Seven feeds formulated to contain 36% protein and 20 kJ g⁻¹ gross energy (dry matter basis), were prepared by replacing fish meal with magmeal. Fifteen fingerlings (initial average weight 2.0 ± 0.1 g) stocked per experimental tank were fed in triplicates at 5% body weight in two portions per day (a level previously established). Growth and food conversion ratio were adequate and comparable without any significant differences (p < 0.5) between feeding groups. Mean values for haematocrit and plasma glucose were not significantly different (p < 0.05) among the feeding groups. Fish group fed control diet (containing highest inclusion level of fish meal and without magmeal) gave the lowest haemoglobin concentration (5.96 ± 0.22 g dl⁻¹). This value was significantly different from other feeding groups. Stressful conditions in fish and in mammals are associated with decreased growth, haematocrit (packed cell volume) and haemoglobin values, increased whole blood glucose (hyperglycaemia) and plasma cortisol concentrations. No such physiological changes were observed in this study. Results suggest that feeding O. niloticus fingerling with magmeal diets did not cause any form of physiological stress. Magmeal can be used as a good alternative protein source in tilapia diets.     

Effects of Dietary Zinc and Calcium on Select Immune Functions of Channel Catfish

Abstract

The effects of dietary zinc and calcium on immunocompetence of channel catfish Ictalurus punctatus (mean initial weight = 3.1 g/fish) were determined after a 10-week feeding trial. Fish were fed daily amounts equal to 3% of their body weight of one of six purified diets that were deficient in zinc (2 mg/kg of diet), calcium (0.02% of diet), or both; replete with zinc (20 mg/kg of diet) and calcium (0.5% of diet); or excessive in zinc (200 mg/kg of diet) or calcium (2.5% of diet). Immunocompetence of immunized and nonimmunized fish fed the various diets was assessed by measuring serum immunoglobulin M levels and mortality after an intraperitoneal injection of live Aeromonas hydrophila. Channel catfish fed diets deficient in zinc, calcium, or both had significantly (P ≤ 0.05) less weight gain and survival as compared with those fed diets replete with or excessive in zinc or calcium. Tissue mineral concentrations of fish indicated that various levels of zinc and calcium nutriture existed when immune functions were tested. Diet affected mortality of only nonimmunized fish in the bacterial-challenge test; zinc deficiency and calcium excess decreased mortality. Whereas growth and survival of fish were reduced by dietary zinc or calcium deficiency, the measured immunological characteristics were not equally impaired by these mineral deficiencies.     

Effect of dietary supplementation of fish oil for lactating sows and weaned piglets on piglet Th polarization

The present study was designed to investigate the effect of dietary fish oil supplementation on piglet T helper cells (Th) polarization in relation to its impact on piglet serum interferon γ (IFN-γ) and interleukin 10 (IL-10) concentrations and splenic expression of Th1/Th2 characteristic genes. The diets of 18 gestating sows were supplemented with 7% lard (C) (n = 10) or 7% fish oil (T) (n = 8) from 10 d before parturition to weaning. At weaning, a split plot experiment was designed, 56 piglets, 28 each from sows fed with fish oil diet or lard diet, were divided into four groups of 7 replicates (one female and one castrated male per replicate) based on both sow diet during lactation and post-weaning piglet diet (C had 7% lard and T had 7% fish oil): CC, CT, TC, TT, and were fed the 7% fish oil or lard diet from day 35 to day 70. Serum concentrations of IFN-γ and IL-10, and Th1/Th2 related genes expression levels in spleen were measured and analyzed. The results showed that piglets fed with fish oil diet during post-weaning tended to have higher serum IFN-γ/IL-10 ratio (P = 0.09) than lard diet fed piglets. Lactation fish oil feeding increased splenic IL-12b, IL-12 receptor β2 (IL-12Rβ2), IL-2 and IFN-γ genes expression (P < 0.05 or P < 0.01) and post-weaning fish oil feeding increased splenic IL-12b (P = 0.06), IL-2 (P < 0.01) and IFN-γ (P = 0.08) mRNA expression than that in lard diet fed piglets at the end of this experiment. On the other hand, IL-4 gene expression (P = 0.01) in spleen was lower in weaned piglet from fish oil diet fed sows than that from lard diet fed sows. However, post-weaning piglets fed fish oil diet had higher splenic IL-4 (P = 0.06), IL-6 (P < 0.01) and IL-10 (P = 0.05) mRNA abundances than that fed with lard diet. These results indicated that dietary fish oil during lactation could increase Th1 polarization and accelerate immune maturation; while 7% fish oil in weaned piglets' diet was likely to increase Th2 cytokines expression.     

Isolation and Pathogenicity of Streptococcus iniae in Cultured Red Hybrid Tilapia in Malaysia

Abstract

This study describes the isolation and pathogenicity of Streptococcus iniae in cultured red hybrid tilapia (Nile Tilapia Oreochromis niloticus × Mozambique Tilapia O. mossambicus) in Malaysia. The isolated gram-positive S. iniae appeared punctiform, transparently white, catalase and oxidase negative and produced complete β-hemolysis on blood agar, while a PCR assay resulted in the amplification of the 16 S rRNA gene and lactate oxidase encoded genes. The isolate was sensitive to tetracycline, vancomycin, and bacitracin but was resistant to streptomycin, ampicillin, penicillin, and erythromycin. Pathogenicity trials conducted in local red hybrid tilapia (mean ± SE = 20.00 ± 0.45 g) showed 90.0, 96.7, and 100.0% mortality within 14 d postinfection following intraperitoneal exposure to 10⁴, 10⁶, and 10⁸ CFU/mL of the pathogen, respectively. The clinical signs included erratic swimming, lethargy, and inappetance at 6 h postinfection, while mortality was recorded at less than 24 h postinfection in all infected groups. The LD_{50-336 h} of S. iniae against the red hybrid tilapia was 10² CFU/mL. The post mortem examinations revealed congested livers, kidneys, and spleens of the infected fish. This is the first report of S. iniae experimental infection in cultured red hybrid tilapia in Malaysia.

Received January 20, 2017; accepted July 16, 2017 Published online October 11, 2017     

Colorimetric Method of Loop-Mediated Isothermal Amplification with the Pre-Addition of Calcein for Detecting Flavobacterium columnare and its Assessment in Tilapia Farms

Flavobacterium columnare, the causative agent of columnaris disease in fish, affects many economically important freshwater fish species. A colorimetric method of loop-mediated isothermal amplification with the pre-addition of calcein (LAMP–calcein) was developed and used to detect the presence of F. columnare in farmed tilapia (Nile Tilapia Oreochromis niloticus and red tilapia [Nile Tilapia × Mozambique Tilapia O. mossambicus]) and rearing water. The detection method, based on a change in color from orange to green, could be performed within 45 min at 63°C. The method was highly specific, as it had no cross-detections with 14 other bacterial species, including other fish pathogens and two Flavobacterium species. The method has a minimum detection limit of 2.2 × 10² F. columnare CFU; thus, it is about 10 times more sensitive than conventional PCR. With this method, F. columnare was detected in gonad, gill, and blood samples from apparently healthy tilapia broodstock as well as in samples of fertilized eggs, newly hatched fry, and rearing water. The bacteria isolated from the blood were further characterized biochemically and found to be phenotypically identical to F. columnare. The amplified products from the LAMP–calcein method had 97% homology with the DNA sequence of F. columnare.

Received May 21, 2014; accepted August 10, 2014     

Replacement of fish meal protein by surimi by‐product protein in the diet of blue gourami Trichogaster trichopterus fingerlings

Based on the nutrient requirement of Trichogaster trichopterus, a fish meal–based basal diet with 350 g/kg diet crude protein and 16.7 MJ/kg energy was formulated, in which the fish meal protein was replaced by surimi by‐product protein at 0.0 (control), 12.5, 25, 50, 75 and 100% levels. The formulated diets were fed ad libitum to T. trichopterus fingerlings (4.80 ± 0.03 g) in triplicate groups for 45 days in a closed water system. Eighteen fibre‐reinforced plastic tanks with 200 l of water were used for rearing the fish. Weight gain, specific growth rate, feed/gain ratio, protein efficiency ratio, nutrient retention and digestibility (protein and energy) of fish were not affected (p > 0.05) up to 50% fish meal protein replacement level by surimi by‐product protein. While whole‐body protein content of fish was marginally decreased, the lipid content was increased with increase in surumi by‐product incorporation level in the diet. The study results suggest that the fish meal protein, which is scarce and costly nowadays, could be replaced up to 50% by surimi by‐product protein in the diet of blue gourami without hampering the growth and nutrient utilization of fish.     

Feeding fodder beet (Beta vulgaris L.) with either barley straw or pasture silage to non-lactating dairy cows

AIMS: To determine the suitability of diets containing either approximately 85% fodder beet (Beta vulgaris L.) with barley straw or 65% fodder beet with pasture silage when fed to non-lactating dairy cows, by measuring intakes, digestibility, rumen function including microbial growth, and N excretion.

METHODS: Holstein-Friesian cows fitted with permanent rumen fistulae were fed either 65% fodder beet with pasture silage (Silage; n=8) or 85% fodder beet with barley (Hordeum vulgare L.) straw (Straw; n=8) in an indoor facility over a 9-day period, for measurement of intakes, digestibility, rumen function and urine production. The cows were adapted to the diets over 2 weeks before the indoor measurements. Feed was available for about 6 hours/day, as practiced commercially for wintering non-lactating cows.

RESULTS: Five cows fed the Straw diet had to be removed from the trial because of acute acidosis; four on Day 1 of the measurement period and one on Day 7. One cow allocated to the Silage diet refused to eat fodder beet bulbs and was also removed from the trial. Two cows fed the Silage diet were also treated for acidosis. DM intakes were lower with the Straw than Silage diets (6.4 (SE 0.4) vs. 8.3 (SE 0.5) kg/day) and organic matter (OM) digestibility was lower with the Straw than Silage diets (77 (SE 1) vs. 83 (SE 1) g/100g). The N content of the two diets was 1.14 and 1.75?g/100?g DM and there was a net loss of N by cows fed the Straw diet (?22.7 (SE 7) g/day). Rumen microbial N production was much lower in cows fed the Straw than the Silage diet (6.6 (SE 1.3) vs. 15.8 (SE 0.7) g microbial N/kg digestible OM intake). Concentrations of ammonia in rumen liquid collected on Days 5–6 were below detection limits (<0.1?mmol/L) in 36/48 (75%) samples collected from cows fed the Straw diet and in 27/48 (56%) cows fed the Silage diet. Mean urinary N excretion was lower in cows fed the Straw than the Silage diet (52.0 (SE 5.8) vs. 87.7 (SE 5.9) g/day).

CONCLUSION AND CLINICAL RELEVENCE: An over-wintering diet for dry cows comprising about 65% fodder beet with 35% pasture silage provided adequate nutrition, although there was some risk of acidosis. In contrast, the diet containing about 85% fodder beet with barley straw resulted in lower DM intakes, poor rumen function, negative N balance so that both nutrition and welfare were compromised.     

Performance of Broilers Fed on Diets Containing Different Amounts of Chaya (Cnidoscolus aconitifolius) Leaf Meal

The performance and gut measurements of broilers fed on diets containing different amounts of chaya (Cnidoscolus aconitifolius) leaf meal (CLM) were examined in two experiments. In the first experiment, 60 Hubbard chickens (30 males and 30 females; 2 weeks old) were fed on five maize diets; these were formulated using 0, 150 (CLM150), 250 (CLM250) or 350 (CLM350) g CLM/kg, and the fifth diet contained soyabean. In the second experiment, 148 Ross male chicks, 1 day old, were fed on three isonitrogenous and isoenergetic maize–soyabean-based diets, which included 0 (control), 150 (C150) or 250 (C250) g CLM/kg. The diets were offered ad libitum for 2 or 3 weeks in the first and second experiments, respectively. Food intake, weight gain and the food:weight gain ratio were recorded. The weight of the gizzard and intestine and the weight and length of the caeca were also determined in the second experiment. In experiment 1, the birds fed on the maize–soyabean diet had a higher (p<0.05) weight gain and final weight than birds fed on maize only or on the CLM150 diets. There were no differences for any of the variables studied between the birds fed on the maize–soyabean diet and those fed on the CLM250, nor between males and females. In the second experiment, weight gain, food intake and the food:weight gain ratio for birds fed on C250 were lower (p<0.05) than those in birds fed on either the control or C150 diets. The weights of the gizzard and intestine were the lowest and the highest, respectively, in birds fed on C250 (p<0.05). The length and weight of the caecum from birds fed on the control diet were lower (p<0.05) than those of birds fed on either the C150 or C250 diets. The results from this study suggest that CLM may be included up to 150 g/kg in commercial diets without having an adverse effect on poultry performance, and may also be mixed with maize up to 250 g/kg to improve the performance of chickens fed on low-protein diets.     

Utilization of diets containing graded levels of ethanol production co‐products by Nile tilapia

A feeding trial was performed to investigate inclusion levels of distillers dried grains with solubles (DDGS) as a fishmeal replacement for juvenile Nile tilapia (Oreochromis niloticus). On a dry matter basis, five isocaloric [19.3 ± 0.4 kJ/g (mean ± SE)], isonitrogenous (39.1 ± 0.5% crude protein) diets were formulated to contain 17.5%, 20%, 22.5%, 25%, and 27.5% DDGS and compared against a 0% DDGS, reference diet (gross energy = 14.5 kJ/g; crude protein = 39.8%). The reference diet resulted in significantly higher body weight gain (BWG), food conversion ratio (FCR), and protein efficiency ratio (PER) than experimental diets except that 17.5% DDGS provided similar FCR and PER. The diet containing 27.5% DDGS had significantly lower FCR and PER values than all other diets even though apparent digestibility did not significantly differ among experimental diets. Although DDGS can be incorporated at higher levels, 20% DDGS provided the highest apparent BWG among experimental diets, while 17.5% promoted the best FCR and PER. Fishmeal may be replaced with low levels of fuel‐based DDGS to reduce feeding cost; however, additional supplements should be considered to enhance fish performance.     

Oral administration of lysine restores food intake and ventromedial hypothalamic dopamine in chicken on a lysine-free diet

1. This study was conducted to examine whether oral administration of lysine solution affect food intake and the ventromedial hypothalamic (VMH) monoamines in chickens fed on a lysine-free diet.

2. Chickens were assigned to four treatment groups. Two groups of chickens were given two different doses of lysine solution (0·1?g and 0·07?g in 1?ml of saline) exogenously (orally) while being fed on a lysine-free diet, and these results were compared with a control diet plus saline group. Another group of chickens was fed on a lysine-free diet without lysine supplementation, and their results were compared with the lysine treated groups. The extracellular dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the VMH of freely moving chicken were measured by in vivo microdialysis.

3. There was no significant difference in food intake between the control diet and the lysine supplemented groups during the time-course of the experiments. Food intake significantly decreased at 4, 5 and 6?h in the lysine-free diet plus saline group compared with the lysine supplemented groups. Of the VMH monoamines, the DA concentration remained close to the baseline in the lysine supplemented groups. This DA concentration was significantly lower than the baseline in the lysine-free diet plus saline group at 3·5?h and thereafter.

4. No significant difference from the baseline was observed for NE in the lysine-free diet plus saline group. The 5-HT concentrations were close to the baseline for all groups throughout the experiments.

5. The findings suggest that oral administration of lysine solution to chickens fed on a lysine-free diet restored food intake which was associated with the variations of VMH DA concentration.