Morphometric relationships and indirect determination of the length frequency structure of the pirarucu, Arapaima gigas (Cuvier), in Brazilian Amazonia

Abstract The pirarucu (giant red fish), Arapaima gigas (Cuvier), (Arapaimidae) is among the diverse fish resources of Amazonia which are threatened by over-exploitation. Little is known about the biology of this species despite its commercial importance. The present paper provides indirect information about the length-frequency structure of the stock which was estimated by sampling its tongue bone in craft shops and weighing fresh mantas (processed fish product) in fish markets since these were the only remaining recognizable features of the fish. The length-frequency reconstruction was carried out using a regression analysis calculated by utilizing individuals caught in experimental fishing.     

Occurrence and treatment of cracked-skull disease affecting Clarias spp. in homestead ponds in Nigeria

Abstract. Cracked-skull disease, previously unrecorded in Nigeria, affected fish in 80% of the homestead ponds investigated in this study. It was peculiar to mud catfish, Clarias spp., under intensive culture in urban Lagos, Nigeria. Male and female fish that were more than 10cm in length were equally vulnerable. The accessory respiratory structures were involved, but the liver, kidney, heart and the other internal organs were not. At its peak, the infection was characterized by a lateral crack in the skull, which resulted in death. Dip treatment in either 2-0ppm potassium permanganate or 0-5ppm formalin (with alcohol) for 30s day ¹resulted in 65-0 and 41-3% full recovery in 7 days, respectively. The implications of the disease for homestead fish culture are discussed.     

奥尼罗非鱼养殖池沉积形成及其主要影响因子的初步研究

在半封闭式奥尼罗非鱼养殖池中投入饲料,探索养殖过程中鱼池沉积形成及其主要影响因子。试验结果表明:无论养鱼或未养鱼,投饲或不投饲,各池均发生不同程度的沉积;外源饲料输入量相同时,养鱼池新颗粒物生成量(干重)比未养鱼池大15.63%,而沉积量比未养鱼池小19.49%;无外源饲料输入时,养鱼池的沉积量比未养鱼池大75.76%;养殖系统内养殖对象与其所处环境的相互依存和相互制约对系统新颗粒物生成及沉积具有重要作用。     

Effect of substrate on progression and healing of skin erosions and epidermal papillomas of Atlantic halibut, Hippoglossus hippoglossus (L.)

Juvenile Atlantic halibut cultured on a smooth substrate often develop skin lesions on the blind (abocular) side, significantly reducing carcass value and causing economic losses. We discovered that fish not only developed skin erosions, but also extensive epidermal papillomas when held on a smooth substrate for 39 months. This is the first time that epidermal papillomas have been reported in Atlantic halibut. To determine whether substrate type affected the progression or healing of these lesions, fish with papillomas and skin erosions were moved to identical rearing units having either an irregular (sand, gravel or Netlon) substrate, or a smooth (gel-coated fibreglass) substrate. After 62 days, 42-50% of fish held on any of the three irregular substrates had a skin erosion area (SEA) that had either diminished or appeared to be completely healed via gross examination. In contrast, none of the fish held on the smooth substrate showed improvement and 75-100% had a more severe SEA. Changes in the papilloma area (PA) were less dramatic: none of the fish held on an irregular substrate had any clear change in PA, although there was a suggestion that the PA in some fish might becoming less severe. Similarly, none of the fish held on the smooth substrate had a change in PA, although there was a suggestion that the PA in some fish was becoming more severe. After 97 days, there was also a suggestion that specific growth rates were higher in fish held on an irregular substrate when compared with those held on the smooth substrate. Overall, these data further substantiate previous studies suggesting that an irregular substrate, including the commercially used Netlon, is best for rearing Atlantic halibut. While there was a clear relationship between substrate type and whether skin erosions or papillomas progressed or healed, the exact cause(s) of these two responses is uncertain. Future studies should focus on risk factors such as stress, burrowing behaviour and the microenvironment of the substrate.     

Transgenic fish: an evaluation of benefits and risks

Transgenic fish have many potential applications in aquaculture, but also raise concerns regarding the possible deleterious effects of escaped or released transgenic fish on natural ecosystems. In this review the potential applications of transgenic fish are considered, the probable benefits reviewed, the possible risks to the environment identified and the measures which might be taken to minimize these risks are evaluated. Growth trials of transgenic fish have already been carried out in outdoor facilities and some of these are discussed in the light of possible risks and benefits. Regarding the hazards associated with release or escape, whilst there is some evidence to suggest that transgenic fish may be less fit compared to their wild counterparts, there is insufficient evidence to say that this will be true in all cases. Using mathematical models, we have attempted to predict the magnitude of the genetic effects in a range of different scenarios. A number of possible containment techniques are considered, amongst which containment by sterility is probably the most promising. This can be engineered either by triploidy or by transgenic methods. The conclusions include a tabulated balance sheet of likely benefits and risks, with appropriate weighting.     

Effects of Varying Levels of High‐Protein Distiller's Grains on Growth Performance of Channel Catfish,Ictalurus punctatus,and Post‐Extrusion Feed Pellet Characteristics

Channel catfish, Ictalurus punctatus, remains the USA's largest aquaculture industry. However, in recent years, high feed prices have negatively impacted profitability. Production of ethanol as a biofuel has increased dramatically. Companies have modified their processes to enhance ethanol yield and these modified processes also increase the crude protein content of the byproduct. The object of this study was to evaluate this high‐protein dried distiller's grains (HP‐DDG) for its suitability in catfish diets. A total of 25 full‐sibling channel catfish (7.1 ± 2.3 g) were randomly stocked into each of twelve 260‐L polyethylene tanks to achieve 25 fish per tank. The control diet was similar to a commercial formulation. Experimental diets contained 20, 40, or 40% HP‐DDG with added lysine (1% of total diet). There were three replicate tanks per diet. Fish were fed to apparent satiation twice daily for 9 wk. Average harvest weights for fish fed the 40% HP‐DDG diet without lysine supplementation (57.0 g) were significantly smaller than that for fish fed the control diet (77.7 g). Average harvest weights of fish fed 20% HP‐DDG (86.8 g) were significantly greater than that of fish fed either 40% HP‐DDG (57.0 g) or 40% HP‐DDG + lysine (73.7 g). There were no significant differences in feed conversion ratios or survivals among treatments, which overall averaged 1.1 and 99%, respectively. These data indicate that HP‐DDG appears to be a suitable ingredient in channel catfish diets up to at least 20% of the total formulation. Data also indicate that inclusion levels of at least 40% HP‐DDG are likely limiting in lysine.     

Cage Culture of Hybrid Striped Bass in Indiana and Evaluation of Diets Containing Three Levels of Dietary Protein1

Culture of hybrid striped bass Morone saxatilis × M. chrysops has been increasing in selected regions of the United States. Because of their thermal tolerance, hybrids may have potential as a new commercial aquaculture species in the Midwest. In these studies, hybrid striped bass were reared in cages located in southern, central and northern Indiana and offered one of three practical diets. Diets contained either 32, 36 or 40% crude protein. Additionally, a preliminary 8 wk laboratory experiment was conducted in which fish were offered the same diets. All diets were formulated to meet the established dietary lysine requirement; optimal levels of other essential amino acids in the diet were predicted by the whole-body essential amino acid profile of hybrid striped bass. In the laboratory experiment, weight gain of fish fed 36% crude protein was significantly higher than those fed either other level of dietary protein. After 205 days, final average weight gains of fish in the field experiment were not significantly different and ranged from 233 to 426 g with an overall average daily gain of 1.6 g/fish/d. Overall survival was 89.1%. Dress-out percentages were 81.2, 69.8, and 34.9% for eviscerated, eviscerated and headed, and fillets, respectively. Those values were not significantly different among dietary treatments or sites. Lipid content of fillets from fish fed 32% dietary crude protein was significantly higher than in fish fed 36 or 40% crude protein.     

Experimental transmission of a salmonid Rhodococcus sp. isolate to juvenile Atlantic salmon, Salmo salar L.

Abstract. This paper provides further characterization of a 'Rhodocoecus' -like pathogen of Atlantic salmon, Salmo salar L., and describes its experimental transmission. An isolate from naturally infected fish was determined to be 'Rhodococcus' -like based on its biochemical profile and from gas liquid chromatography assessment of its cellular fatty acid methyl esterase profile in comparison to a data base. This isolate was used in an infectivity trial in which Atlantic salmon juveniles received an intraperitoneal injection of known concentrations of the bacteria. Fish receiving 0.5 ml of a 10⁹bacteria ml⁻¹ solution developed severe peritoneal granulomatous reactions, and bacteria were recovered from the peritoneum and the kidney. In contrast to the natural disease, in which pathological changes are often most dramatic in the renal interstitium, in our study, the lesions were restricted to the injection site—the peritoneal cavity. However, in this location, the large colonies of bacteria and the nature of the host response were both characteristic of the changes noted in the renal interstitium of naturally infected fish. Lesser concentrations of injected bacteria resulted in either no or minimal pathological change, and subsequent recovery of bacteria from injected fish was poor. Horizontal transmission to non-injected co-habitants was not achieved.     

Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~ 0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9–10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon.     

Salmonid gill bacteria and their relationship to amoebic gill disease

16S ribosomal RNA gene analysis was used to assess the bacterial community associated with Atlantic salmon, Salmo salar L., gills which were either affected by amoebic gill disease (AGD) or were AGD-negative, in order to determine the role that bacteria may play in the development of AGD. AGD-positive specimens were either infected in the laboratory with Neoparamoeba pemaquidensis, the causative agent of AGD, or were obtained from commercial salmon cages. Samples from laboratory fish maintained in sea water possessed a marine-type community while field samples which had been treated by a series of freshwater baths possessed a more diverse community which included variable proportions of different bacterial ecotypes, including groups typically associated with soil, skin surfaces and faeces. Samples from fish infected with AGD in the laboratory and a sample from one of two salmon cage fish specimens were dominated by a phylotype belonging to the strictly marine bacterial genus Psychroserpens (family Flavobacteriaceae, phylum Bacteroidetes). The phylotype was not detected in any of the AGD-negative samples or in one of two AGD-positive samples obtained from fish subjected to temporary freshwater immersion. The possibility of certain Psychroserpens species as potential opportunistic pathogens associated with salmonid AGD is proposed.     

AFLP and microsatellites as genetic tags to identify cultured gilthead seabream escapees: data from a simulated floating cage breaking event

Genetic discrimination using DNA fingerprinting is rapidly developing for cultured stock and wild fish populations. Microsatellites and AFLPs are being widely used in aquaculture to assign fish or processed fish products, to their claimed origin, paternity or strain. In the present study, 147 AFLP and 4 microsatellite markers were used as genetic tags in gilthead seabream, Sparus auratus. Specimens from two different hatchery broodstocks (one of Atlantic and one of Mediterranean origin) and wild fishes from a natural population were fingerprinted. Putative offspring from these broodstocks were computer-generated, and the confidence in the parentage assignment of their genetic profiles to the hatchery broodstock assessed. The virtual offspring were then mixed with specimens from a natural population to simulate an accidental escape from a floating cage. The risk of false paternity inclusion was evaluated to test the ability to identify either Atlantic or Mediterranean hatchery offspring among wild fish. The method proved to be reliable, and could therefore be used to forecast the impact of fish farm escapees.     

The Irish sea trout enhancement programme: an assessment of the parr stocking programme into the Burrishoole catchment

The success of the sea trout, Salmo trutta L., enhancement programme carried out in the Burrishoole catchment in the west of Ireland from 1993 until 1998 is reviewed in terms of the number of fish stocked, the number of fish which migrated to sea and the number which returned from sea during this period. The success of the programme is also evaluated in terms of the cost of producing parr for stocking and the subsequent value of returning post-smolts (0+ sea age) and rod caught fish. A total of 49 235 tagged fish were released into Lough Feeagh, between 1993 and 1998. Of these fish, 14 788 were microtagged and the remainder, 34 447 had either elastomer or alphanumeric visible implant (VI) tags. Tag loss rates at release varied from 3 to 5.7%. Over the course of the programme a maximum of 7801 fish migrated through the traps towards sea, of which 581, or 7.4%, returned. In any 1 yr a maximum 13.1% of fish returned from sea. The average cost of producing a parr for stocking out was €1.15, which translated into average values of €8.16 per smolt and €169 per returning post-smolt.     

The relationships between fish health, metabolic rate, swimming performance and recovery in return-run sockeye salmon, Oncorhynchus nerka (Walbaum)

The repeat swimming ability and oxygen uptake (Mo2) of adult sockeye salmon, Oncorhynchus nerka (Walbaum), were assessed at ambient water temperatures at three field locations along their migration route. Following these measurements, internal and external fish condition was evaluated according to United States Environmental Protection Agency guidelines. Here we report on the physiological characteristics of fish having either moderate or severe levels of disease and injury. Routine oxygen uptake (Mo2) did not differ between healthy fish and those with indices of ill health. In contrast, fish classified as sick, which included conditions of damaged internal organs, an Ichthyophonus spp. heart infection, a Saprolegnia spp. gill infection, and skin wounds, had a lower post-exercise Mo2 and were unable to repeat their critical swim speed (U(crit)) on the second swim test. Moderate levels of disease or injury did not significantly affect either U(crit) or post-exercise Mo2. We conclude that the ability of adult salmon to recover quickly from exercise may be a useful indicator of sublethal pathologies.     

Metabolic fate of <Superscript>14</Superscript>C-labelled chlorinated and non-chlorinated fatty acids in goldfish (<Emphasis Type="Italic">Carassius auratus</Emphasis>)

In order to study the metabolic fate of chlorinated fatty acids in fish, goldfish were fed either 9,10-dichlorostearic acid or oleic acid, chosen as the unchlorinated analogue, both radiolabelled at either the carboxyl (1st) or the terminal (18th) carbon of the fatty acid chain. By keeping the fish in hermetically closed aquaria, all the respired, assimilated and excreted radioactivity could be accounted for. Fish fed 9,10-dichlorostearic acid labelled in the terminal end respired radioactive CO₂ to a much lower degree than fish fed the other test compounds. As a consequence, the radioactivity bound in lipids was higher in the group of fish fed dichlorostearic acid labelled in the terminal end. It is suggested that the chlorine atoms in the middle of the carbon chain obstruct the metabolic turn-over of 9,10-dichlorostearic acid, which may have an impact on the residence time of these compounds in the ecosystem.     

Evaluation of the Effects of Different Stunning Methods on the Stress Responses and Meat Quality of the Amazon hybrid surubim,Pseudoplatystoma fasciatum female × Leiarius marmoratus male

Different stunning methods (carbon dioxide [CO₂] and hypothermia) used in industrial fish processing were compared with asphyxia in air, which is used in traditional fishing, to evaluate the effects of these methods on the stress responses and the meat quality of the Amazon hybrid surubim, Pseudoplatystoma fasciatum female × Leiarius marmoratus male. After the application, blood and behavioral indicators were evaluated. Following death by gill cutting, the fish were gutted, and analyses of muscle pH, rigor mortis, the exudation of the meat, and coloration were performed. Significantly higher levels of cortisol and glucose were exhibited by the fish subjected to asphyxia than by the fish stunned by either CO₂ or hypothermia. The fish subjected to asphyxia displayed decreasing muscle pH during the first 2 h after death and showed higher rates of rigor mortis after 3 h than the fish that were stunned by the other two methods. The asphyxia is a practice that exposes fish to suffering by causing an increase in stress responses, which affects meat quality. The immersion of fish in water and ice (hypothermia) for 5 min was more effective stunning method than the use of CO₂, resulting in higher loss of sensibility and greater welfare.     

Bactericidal activity of cecropin B and cecropin P1 expressed in fish cells (CHSE-214): application in controlling fish bacterial pathogens

Cecropins are a group of antimicrobial peptides which have bactericidal activity against a broad range of bacteria. To date, the cecropins used in a variety of studies were either purified from their natural source or obtained by chemical synthesis. The present study was conducted to test whether bactericidally active cecropins could be expressed in a fish cell line. For this purpose, Chinook salmon embryo cells (CHSE-214) were transfected with cecropin transgene constructs: Hyalophora cecropia preprocecropin B, procecropin B, cecropin B, and porcine P₁ cecropin. From the transfected cells, single cell clones were selected and screened for the presence of cecropin gene constructs by PCR amplification. The expression of the cecropin transgene in the PCR positive clones was determined by RT-PCR reaction. Southern blot hybridization results showed that the cecropin gene constructs were integrated into the genome in a multiple integration pattern. Bactericidal activity of the cecropins, synthesized from transgene constructs, was detected using inhibition zone assay for fish pathogenic bacteria: Aeromonas hydrophila, Pseudomonas fluorescens, and Vibrio anguillarum. Cecropin antimicrobial peptides produced in CHSE-214 cells possess bactericidal activity against these three fish pathogenic bacteria.     

Vitamin E sparing effect by dietary vitamin C in juvenile hybrid tilapia, Oreochromis niloticus×O. aureus

In order to investigate sparing effects of vitamin C on vitamin E for juvenile hybrid tilapia, fish were fed diets with or without vitamin E each supplemented with either adequate or a high (3× adequate) level of two ascorbate sources, -ascorbic acid (AA) and its derivative, -ascorbyl-2-monophosphate-Mg (C2MP-Mg). Each diet was fed to three replicate groups of fish initially weighing a mean value of 0.54±0.01 g/fish in a closed-recirculated rearing system for 8 weeks. Weight gain and feed efficiency of fish fed the vitamin E-deficient diet supplemented with adequate levels of either AA or C2MP-Mg were significantly lower (P<0.05) than fish fed the other diets. Plasma and liver -tocopherol concentrations were lower in fish fed vitamin E-deficient diets regardless of the level or source of supplemented ascorbate. Gill -tocopherolxxxxxxxx concentration was highest in fish fed vitamin E-adequate diets, intermediate in fish fed vitamin E-deficient diets supplemented with a high level of AA or C2MP-Mg and lowest in fish fed a vitamin E-deficient diet supplemented with an adequate level of AA or C2MP-Mg. Fish fed a vitamin E-deficient diet supplemented with an adequate level of AA or C2MP-Mg had higher hepatic thiobarbituric acid-reactive substances than fish fed the other diets. These data suggest that the high supplementation level (3× adequate) of ascorbate could spare vitamin E in diets for hybrid tilapia and that both AA and C2MP-Mg exhibits the same sparing effect.     

Supplemental effect of cholyltaurine and soybean lecithin to a soybean meal-based fish meal-free diet on hepatic and intestinal morphology of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

The supplemental effects of cholyltaurine and soybean lecithin to a defatted soybean meal (SBM)-based fish meal-free diet on the hepatic and intestinal morphology of rainbow trout Oncorhynchus mykiss were investigated. A fish meal-based diet (FM), three fish meal-free diets supplemented either with soybean lecithin (SL), bovine gall powder (BG) or cholyltaurine (C-tau) and an unsupplemented fish meal-free diet (NFM), were given to fish (−11 g) for 10 weeks. The growth was the lowest in fish fed diet NFM, intermediate in fish fed diet SL and the highest in fish fed diet FM, BG and C-tau. Hepatocytes of fish fed diet NFM were atrophied, and the distal intestine of these fish showed abnormal features: disintegrated microvilli and fatty degeneration in epithelial cells and increased amount of connective tissue in the submucosa. Hepatic and intestinal histological features in fish fed diets SL, BG and C-tau were similar to those in fish fed diet FM. These results indicate that soybean lecithin, bovine bile salts and cholyltaurine have similar effects on normalizing the hepatic and intestinal morphologies of rainbow trout fed the SBM-based diet, although growth promotion effect was limited in the soybean lecithin.     

Effects of Feeding Frequency and Handling on Growth and Mortality of Cultured Walking Catfish Clarias fuscus

Two experiments were conducted to study the effects of feeding frequency on growth, and of handling stress on growth and mortality, in intensive tank culture of the walking catfish Clarias fuscus . In the first experiment, fish were grown from an initial weight of 37 g for 34 d. A fixed ration of 3.0% body weight per day was divided into either 1, 2, or 3 feedings per day, and fish were either handled weekly or left unhandled for the entire experiment. Fish given 3 feedings per day experienced 19% faster growth ( P < 0.05) than fish given the same ration in a single feeding per day. These differences in growth reflect differences in assimilation efficiency, assuming all other metabolic costs were constant among treatments. Handling of individuals caused decreased growth; however, there was no effect on mortality.
In the second experiment, fish were grown from an initial weight of 78 g for 29 d. Fish were fed either 1 or 2 satiation feedings per day and were either handled weekly or left unhandled for the entire experiment. Fish fed 2 satiation feedings per day experienced 47% faster growth ( P < 0.05) than fish fed 1 satiation feeding per day, which was assumed to reflect a higher level of food consumption. No effect of handling on either growth or mortality was observed for fish in experiment 2. Multiple meals per day also reduced depensatory growth among individuals in both experiments.     

Availability of phosphorus and trace elements in low-phytate varieties of barley and corn for rainbow trout (Oncorhynchus mykiss)

Approximately two-thirds of phosphorus in various grains is present as phytate, which is not well-utilized by fish and other monogastric species. Besides its low availability of phosphorus, phytate is reported to reduce the availability of other dietary nutrients to animals. Single-gene, non-lethal low phytic acid (lpa) mutations in corn and barley cause the seed to store most of the phosphorus as inorganic phosphorus instead of as phytate phosphorus. Theoretically, using these mutant grains containing lower levels of phytate in animal feeds should reduce phosphorus excretion by the animals, provided that available phosphorus levels in feeds containing these grains are appropriately adjusted downward. This study was conducted as a first step to determine if the biological availability of phosphorus in the low-phytate mutants of barley, dent corn and flint corn differed significantly from that in ordinary grains for fish. Also of interest was the effect, if any, on the availability of other minerals in formulated feeds containing the low-phytate grains. Feeding trials demonstrated that the apparent availability of phosphorus in low-phytate grains was significantly higher than that in ordinary grains when they were combined with low-ash ingredients. Fecal phosphorus content (on average) decreased 50.2% (in phytate-phosphorus) or 42.9% (in total phosphorus) by replacing ordinary grains with low-phytate grains in the low-ash diets. The apparent availabilities of calcium, iron, zinc and strontium also were significantly higher in the low-ash diet containing low-phytate dent corn than that containing ordinary dent corn. However, no such increase was observed with low-phytate barley or low-phytate flint corn over their counterpart grains in either calcium, iron or zinc. The apparent availabilities of copper, manganese, magnesium, potassium and sodium were not significantly different between ordinary and low-phytate grains. The apparent digestibility of dry matter also was not significantly different between ordinary and low-phytate grains. The results of this study suggest that a substantial reduction of phosphorus discharge from fish, poultry and animal farms could be achieved simply by replacing ordinary grains with low-phytate mutant grains in low-ash feeds.