Harry K. Dupree Stuttgart National Aquaculture Research Center

The large area of rice ( Oryza sativa L.) production worldwide is critical to the well being of large numbers of the world's people. Yet for rice, the most important single plant species for human nutrition, there is not a widely used growth staging system. Despite good points of the published rice growth staging systems, none has been used widely for describing rice growth and development. Consequently, an objective growth staging system with enumeration adapted to cumulative leaf number (CLN) would improve communication among scientists, farmers, and educators. We propose a rice developmental staging system divided into three main phases of development: seedling, vegetative, and reproductive. Seedling development consists of four growth stages: unimbibed seed (S0), radicle and coleoptile emergence from the seed (S1, S2), and prophyll emergence from the coleoptile (S3). Vegetative development consists of stages V1, V2 … V N ; N being equal to the final number of leaves with collars on the main stem. Reproductive development consists of 10 growth stages based on discrete morphological criteria: panicle initiation (R0), panicle differentiation (R1), flag leaf collar formation (R2), panicle exertion (R3), anthesis (R4), grain length and width expansion (R5), grain depth expansion (R6), grain dry down (R7), single grain maturity (R8), and complete panicle maturity (R9). Assigning rice growth stages based on discrete morphological criteria will result in unambiguous growth‐stage determination. For example, using this system, two people staging the same plant will arrive at the same growth stage. This is because the system exploits the presence or absence of distinct morphological criteria in a symbolic logic dichotomous framework that only permits yes or no answers.

The gut microbiome of vertebrates plays an integral role in host health by stimulating development of the immune system, aiding in nutrient acquisition and outcompeting opportunistic pathogens. Development of next-generation sequencing technologies allows researchers to survey complex communities of microorganisms within the microbiome at great depth with minimal costs, resulting in a surge of studies investigating bacterial diversity of fishes. Many of these studies have focused on the microbial structure of economically significant aquaculture species with the goal of manipulating the microbes to increase feed efficiency and decrease disease susceptibility. The unravelling of intricate host-microbe symbioses and identification of core microbiome functions is essential to our ability to use the benefits of a healthy microbiome to our advantage in fish culture, as well as gain deeper understanding of bacterial roles in vertebrate health. This review aims to summarize the available knowledge on fish gastrointestinal communities obtained from metagenomics, including biases from sample processing, factors influencing assemblage structure, intestinal microbiology of important aquaculture species and description of the teleostean core microbiome.

Abstract Many classical therapeutants are going to be banned in Europe, and an urgent need for alternatives is emerging. This issue can be exemplified by one major parasitic disease in aquaculture and ornamental fish breeding: velvet disease. This disease, caused by dinoflagellates of the genera Amyloodinium and Piscinoodinium , is an important infection affecting cultured freshwater and marine ornamental and food fish, and consistently causes great financial loss to the associated industries. Therapeutants available contain copper, malachite green, or methylene blue, and which can be toxic to non‐target organisms in the surrounding environment. As a result, these chemicals are banned for use by the aquaculture industry in several countries, and a prohibition for commercial ornamental fishkeeping is likely to follow in most countries. Increasing development of resistance to therapeutants, and growing public awareness for animal welfare and environmental protection, have prompted research in the areas of alternative treatment options and immunostimulants. Hydrogen peroxide and peracetic acid are possible ‘green’ therapeutants which do not contribute residues to the environment. Natural feed supplements such as pre‐ and probiotics can increase animal welfare and prevent stress and/or infections. Humic substances are another promising, natural immunostimulants which will be considered in depth. The aim of this review is to provide an overview of risks and benefits of current treatment options and new approaches to replace harmful therapeutants and minimize the number of toxic residues discharged into the environment. Treatments will be discussed on various parasitic infections and focus, where available, on Amyloodinium and Piscinoodinium .

This study was designed to evaluate the effects of dietary supplementation with brewers yeast (Brewtech®) and nucleotides (Optimûn), either singularly or in combination, on red drum growth, body composition, stress responses and possible resistance to Amyloodinium ocellatum infection. Juvenile red drum (∼1 g initially) fed practical fish-meal-based diets for 6 weeks had similar weight gain regardless of whether the diet was unsupplemented (basal) or supplemented with brewers yeast (2% of diet), nucleotides (Optimûn at 0.2% of diet) or both brewers yeast (2% of diet) and nucleotides (Optimûn at 0.2% of diet). Dietary effects on hepatosomatic index, intraperitoneal fat ratio or whole-body composition were not significant, except that fish fed the singular nucleotide supplement had a significantly higher whole-body lipid content compared with fish fed the basal diet. No significant dietary effects on cortisol response were observed after a 15 min confinement stress test perhaps because of the extreme variation among individual fish. Subsequently, in situ challenge by co-habitation with A. ocellatum caused 100% mortality regardless of dietary treatment within a 48 h period. It is concluded that dietary supplementation of brewers yeast and nucleotides did not promote enhanced growth or improved cortisol response and resistance to uncontrolled amyloodiniosis in juvenile red drum, at least at the tested dosages.

Abstract Physiological stress is a nonspecific response common to all vertebrate organisms initiated by many types of environmental changes. Stress in fish can be characterized by physiological changes such as plasma cortisol, glucose, lactate, and electrolyte concentrations and is quantitatively related to the severity and longevity of the stressor. A hierarchy is evident among the physiological changes, such that adrenalin from activation of the sympathetic nervous system is released most rapidly, followed by cortisol, and then glucose. Plasma electrolyte disturbances may not occur until the stress is severe and present for an extended time. Adrenalin increases plasma glucose by stimulating liver glycogenolysis, which represents a metabolic energy cost to the fish. The functions of cortisol include possible induction of gluconeogenesis and suppression of the inflammatory response. Maintaining osmoregulatory homeostasis is an energetically expensive process, and disturbances deplete energy reserves. Recent experiments have shown the importance of distinguishing between acute and chronic responses to stress. Acute responses to stressors may be beneficial to the fish and extend their normal adaptive ability, whereas chronic exposure to stressful conditions may result in decreased performance or survival. The physiological stress response in fish culture has been shown to be altered by hatchery conditions and genetic selection. Management practices and selection pressures affect the stress response, which requires that the ultimate use of the fish be considered during rearing. Commercial food fish aquaculture, which involves rearing fish at very high densities, requires minimizing stressors such as water-quality deterioration, disease treatment, and handling to maintain healthy growing fish. Fish raised for stocking into the wild might benefit from a more robust stress response to prepare them for survival in a natural environment. Present information does not allow for the selection of the most desirable stress response profile that would benefit fish reared for different purposes.

The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.

Centrocestus formosanus, the gill trematode, has caused serious losses among fish raised by tropical fish producers since the early 1980s and is believed to be harmful to wild fish populations, including the federally listed endangered fountain darter (Etheostoma fonticola), in the Comal River near San Marcos, Texas. The parasite appears to infect in many fishes from Hawaii, Florida, Texas, and Utah. The gill trematode has a complex life cycle involving definitive hosts (aquatic birds and occasionally some mammals) and intermediate hosts (aquatic snails and several fish species). In the United States, the green heron (Butorides virescens) and the great egret (Ardea alba) serve as definitive hosts. The first intermediate host, the red-rim melania (Melanoides tuberculatus), an exotic snail, has been found in 15 southern and western states. This snail exhibits resistance to desiccation, molluscicides, and disinfectants and has been documented to out-compete established mollusks. Both the gill trematode and its exotic snail host continue to spread in the United States.

Ichthyophthirius multifiliis is a protozoan that may infest and significantly damage cultured fish species. The purpose of this study was to measure the efficacy of copper sulfate in treating ichthyophthiriasis. Fingerling channel catfish Ictalurus punctatus exposed to at least 2,000 theronts of I. multifiliis per liter of water developed consistent infestations of I. multifiliis (20 or more trophonts on the dorsal surface of the head of the fish). Infestation was observed in untreated controls at day 5 after exposure and mortality occurred after day 10. Coexposure studies with theronts and different concentrations of copper sulfate revealed that all theronts were killed at concentrations greater than 0.05 mg/L. To determine the effect of copper sulfate in the treatment of ichthyophthiriasis, fish were exposed to the parasite until trophonts were observed (day 5), and they were subsequently treated with copper sulfate. The lowest effective concentration of copper sulfate for treatment of ichthyophthiriasis (i.e., after infestation was observed in the fish) was 0.4 mg/L. To assess the effects of various water quality conditions on copper treatment, total suspended solids (TSS) and pH were varied during treatment of ichthyophthiriasis. Concentration of TSS was inversely correlated to the efficacy of copper sulfate for I. multifiliis infestations, whereas no relationship was observed between pH and efficacy of a single copper sulfate dose. The results indicated that copper sulfate can be used to treat ichthyophthiriasis at concentrations of 0.4 mg/L for at least 5 d under the specific water conditions used in this study (pH, 7.45 ± 0.27; temperature, 20.5 ± 0.7°C; alkalinity, 176.6 ± 28.1 mg/L as CaCO3) and that efficacy of copper sulfate was affected more by TSS concentration than by pH.

Abstract Largemouth bass Micropterus salmoides are piscivorous fish raised on farms then sold live in Asian fish markets on the east and west coasts of the United States. In the winter of 1998, a major producer of feed‐trained bass suffered a significant increase in fish mortality both during shipping and while the fish were still in ponds. No bacterial, viral, or significant parasitic pathogens were found at necropsy. Livers of affected fish were pale and translucent with 3–10 mm pink nodules on their surface and deeper in the parenchyma. Histological examination of these livers showed that the translucent regions of the liver contained few hepatocytes and were composed of tissue consistent with a chronic inflammatory response. Also present were eosinophils, islands of pancreatic and biliary cells, and granulomas that did not stain positively for mycobacteria. The pink nodules were areas of multifocal regeneration of normal hepatocytes. Sequential studies of bass in ponds revealed that the bass were progressively accumulating glycogen in their hepatocytes to an extent sufficient to explain the massive necrosis of that organ. In order to determine the effect of diets varying in available carbohydrate on fish growth, survival, and liver glycogen content, a 12‐wk feeding trial was conducted in aquaria with juvenile largemouth bass. Nitrogen‐free extract values indicated that an extruded trout diet, a steelhead trout diet, and a diet designed to contain 45% protein and 25% fat, contained 35, 27, and 21% carbohydrate, respectively. Weight gain was lowest in fish fed the extruded trout diet, while liver glycogen was significantly higher in fish fed diets with >27% carbohydrate than in fish fed the diet with 21% carbohydrate. The farmer switched to a diet similar to the 45–25 diet used in our trial. Subsequently, 16‐mo‐old fish examined in October 2000 had no hepatic nodules or necrosis, were significantly larger and less variable in size than previous crops, and the farmer experienced no significant losses in ponds or during shipping.

Gills of 194 fountain darters Etheostoma fonticola collected from the Comal River in Texas from May 1997 through May 1998 were found to be parasitized with 8–1,524 metacercarial cysts of a heterophyid trematode tentatively identified as Centrocestus formosanus. The intensity of infection varied among three sites on the Comal River. In contrast, of 130 darters from the nearby San Marcos River that were examined, only 4 (3%) were infected, and these had 1–2 cysts per fish. Of 2,279 Melanoides tuberculata snails from the Comal River that were examined, 139 (6.1%) were infected with the trematode. Only 1 snail in 2,241 from the San Marcos River that were examined was infected. The presence of metacercariae in darters was associated with flared opercula, shortened or thickened gill filaments, epithelial hyperplasia, and engorged lamellae. The normal cartilage support of the filaments was distorted and displaced, leading to severe deformities of filament structure. Gill damage was severe and possibly life threatening for the darters with more than 800 cysts per fish (9% of examined fish). We suspect that fountain darter deaths were caused by the parasite in the Comal River during this study.

On 16 November 1963, the U. S. Fish and Wildlife Service Fish Farming Experimental Station at Stuttgart, Arkansas, became the first institution to import grass carp (Ctenopharyngodon idella) into the United States. This introduction was the result of at least seven years of effort to find an effective biological control for problematic aquatic weeds. The introduction was in keeping with a strong environmental and political mandate of that day to replace the broad use of chemicals with biological controls. For about 10 years, federal and state agencies and university systems strongly promoted introductions, spawning, and nationwide stocking of the grass carp. In 1966, the USFWS laboratory at Stuttgart, Arkansas, was apparently responsible for the first accidental release of grass carp to the environment. By 1972, grass carp were stocked in open water systems, documented in 16 states, and established in the Mississippi River system. All this occurred before the first private-sector commercial producers received and spawned the fish in 1972 and 1973, respectively. From 1972 to 1985, public agencies were actively involved in research to produce non-reproductive grass carp for stocking purposes and in 1983, in conjunction with a private producer, these efforts led to the development of triploid grass carp. In 1985, an official U.S. Fish and Wildlife Service biological opinion was rendered that grass carp triploids were an environmentally safe, weed-controlling fish. In the same year, the U.S. Fish and Wildlife Service established a triploid grass carp ploidy inspection program that opened the way to ship certified triploid grass carp around the country. From 1985 to 2005, more than 7 million triploid grass carp were shipped throughout the United States. With grass carp now officially recorded from 45 states it is important to be aware of (or remember) the facts surrounding its introduction, early spread, present usage, and need. Understanding these will in turn will allow for more rational decisions to be made concerning the future of these fish.

Abstract— A pair of experiments were performed to assess amino acid supplementation of pet food grade poultry by-product meal for utilization as the sole protein source for hybrid striped bass Morone chrysops×M. saxatilis. The first experiment determined the available amino acids from menhaden fishmeal and poultry by-product meal for hybrid striped bass. The second experiment determined the efficacy of supplementing poultry by-product meal with amino acids based on an ideal amino acid profile of hybrid striped bass muscle. The positive control diet contained 40% digestible protein solely from menhaden fishmeal and the negative control diet contained 40% digestible protein solely from pet food grade poultry by-product meal. The negative control diet was additively supplemented with lysine, methionine, threonine, and leucine at 1.16,0.57,0.31 and 0.47% of the diet, respectively. Lysine supplementation alone did not improve fish performance based on any measured response. Moreover, the negative control diet and the lysine supplemented diet had lower weight gain and feed efficiency than the positive control diet. Supplementation of the diet containing pet food grade poultry by-product with lysine and methionine; lysine, methionine, and threonine; or lysine, methionine, threonine, and leucine improved weight gain and feed efficiency above that of the negative control diet. The diet containing poultry by-product supplemented with lysine, methionine, and threonine produced weight gains statistically indistinguishable from those of the positive control diet. Protein and energy retention efficiencies also improved with supplementation of at least lysine and methionine and were statistically indistinguishable from those observed in fish fed the positive control diet. Supplementation with lysine and methionine reduced the hepatosomatic index to levels similar to those found in fish fed the menhaden fishmeal diet. Intraperitoneal fat levels were similar among treatments (6.1-6.6%) with the exception that fish fed the diet supplemented with lysine, methionine, and threonine exhibited lower (5.5%) fat levels. Supplementing the poultry by-product meal diet with only lysine and methionine increased muscle ratio to levels equivalent to those found in fish fed the positive control (fishmeal) diet. In conclusion, amino acid supplementation of pet food grade poultry by-product meal can be used to replace fishmeal in diets for hybrid striped bass without a reduction in fish performance.

Two primary ways to achieve low-cost, nutritionally efficacious diets for sunshine bass (Morone chrysops × M. saxatilis) are to decrease crude protein (CP) levels and the use alternative animal or plant ingredients to partially, or totally, replace fish meal. A 459-day feeding trial was conducted with juvenile (35 g) sunshine bass to evaluate growth, feed efficiency, size distribution at harvest, immune function status and body composition when fed diets containing soybean meal (SBM), feed-grade poultry by-product meal (PBM), and supplemental methionine as complete replacements for menhaden fish meal (MFM) at 300 g kg−1 diet, while simultaneously reducing dietary crude protein (CP; 320, 360, and 400 g kg−1). The feeding trial was conducted in 12, 0.04-ha earthen ponds stocked at a rate of 300 per pond (3000/ac). At 400 g kg−1 dietary protein, there were no differences in responses between fish fed the diet containing MFM or the diet in which MFM was completely replaced with PBM and supplemental methionine on a digestible protein basis. However, final mean weight, percentage weight gain, specific growth rate, and protein efficiency ratio were linearly related (P < 0.10) to dietary protein level in the diets while no significant differences were found in feed intake and feed conversion ratio. The expected odds of fish at harvest being classified into larger size categories (> 680 g) decreased as dietary protein level decreased based on ordinal logistic regression. There were no significant relationships between body compositional indices and dietary treatments. Body fat ranged from 56 g kg−1 to 62 g kg−1, single fillets ranged from 28% to 30%, and livers ranged from 2.45% to 2.62% of body weight across treatments. Fillet protein concentration was positively linear and quadratic for protein level in the diet but fillet moisture, lipid and ash did not differ among diets. Total serum protein, immunoglobulin and lysozyme activity decreased linearly with decreasing diet protein level. These results suggest that complete replacement of MFM with feed grade PBM and supplemental methionine is possible in diets for sunshine bass and that further reductions in dietary protein level may be possible with amino acid supplementation.

Abstract The digestibility of nutrients and energy in various ingredients to fish is affected by a variety of factors including ingredient quality and processing. Limited information is available regarding the digestibility of nutrients in feedstuffs for sunshine bass Morone chrysops ♀× M. saxatilis ♂. This information is particularly needed to improve the accuracy of diet formulations and allow appropriate substitution of feedstuffs. Therefore, a study was conducted with advanced sunshine bass fingerlings (50–75 g) to determine the apparent digestibility coefficients (ADCs) for protein, lipid, carbohydrate, gross energy, and organic matter in a variety of feedstuffs in extrusion‐processed diets. Included in the study were low‐temperature processed menhaden fish meal (Select®), meat and bone meal, fish meal analog (PROPAK™) dehulled soybean meal, cottonseed meal, corn grain, sorghum, wheat flour, wheat middlings, and rice bran. Test diets consisted of a 70:30 mixture of reference diet to test ingredient with chromic oxide (0.8%) as the inert marker. Reference and test diet ingredients were mixed in a commercial ribbon blender, preconditioned and extruded on a Wenger X‐20 to produce a neutrally buoyant pellet (5 mm). The digestibility trials were conducted in six 600‐L rectangular tanks connected as a closed recirculating brackish (5–7 ppt) water system. Diets were randomly assigned to tanks of 45–50 sunshine bass and fed twice daily to satiation. Feedstuffs of high‐protein and high‐lipid content were better digested by sunshine bass than feedstuffs of high carbohydrate or high fiber content. Organic matter digestibility ranged from 42% for both sorghum and corn to 96% and 98% for meat and bone meal and Select™ menhaden fish meal, respectively. Select™ menhaden fish meal and meat and bone meal appeared to be the best Ingredients for sunshine bass diets in terms of overall nutrient profiles and digestibility of nutrients. The fish meal analog did not perform as favorably as the other two animal products. Protein and lipid of cottonseed meal were highly available to sunshine bass with ADCs of 85% and 92%, respectively. Protein digestibility was high for soybean meal (77%), whereas the digestibility of organic matter (51%), lipid (54%), carbohydrate (25%) and energy (56%) in this feedstuff was moderately low. Energy in wheat middlings and wheat also was moderately available at 67% and 59%, respectively. Energy in sorghum and corn was much less available at 44% and 40%, respectively. Digestibility of nutrients and energy in rice bran exceeded 90%. Use of this information should aid the development of more efficient and economical diet formulations for sunshine bass.

Short-term feed deprivation (or fasting) is a common occurrence in aquacultured fish species whether due to season, production strategies, or disease. In channel catfish (Ictalurus punctatus) fasting impacts susceptibility to several bacterial pathogens including Flavobacterium columnare, the causative agent of columnaris disease. As columnaris gains entry through the gills and skin of fish, we examined here changes in transcriptional regulation induced in these surface mucosal tissues due to short-term (7 day) fasting. RNA-seq expression analysis revealed a total of 1,545 genes perturbed by fasting. Fasting significantly altered expression of critical innate immune factors in a manner consistent with lower immune fitness as well as dysregulating key genes involved in energy metabolism and cell cycling/proliferation. Downregulation of innate immune actors such as iNOS2b, Lysozyme C, and peptidoglycan recognition protein 6 is predicted to impact the delicate recognition/tolerance balance for commensal and pathogenic bacteria on the skin and gill. The highlighted expression profiles reveal potential mechanistic similarities between gut and surface mucosa and underscore the complex interrelationships between nutrition, mucosal integrity, and immunity in teleost fish.

The refinement of hybrid striped bass feed formulations has been progressing rapidly. There is still, however, limited information available regarding nutrient digestibility and amino acid availability from common feedstuffs. A pair of experiments was conducted to determine the protein digestibility and amino acid availability to sunshine bass from an assortment of commercially available animal protein feedstuffs, blended animal products and plant protein feedstuffs in extruded diets. The feedstuffs tested were blood meal, poultry by-product meal, fish solubles, Pro-Pak 60, Pro-Pak 65, ProCon 65RDB, and 60FMC for the animal protein feedstuffs and brewer's yeast, canola meal, peanut meal, and sunflower meal for the plant protein feedstuffs. Test diets consisted of a mixture of nutritionally complete reference diet and test ingredient. Triplicate tanks of fish were fed their respective diets for 7 days prior to collection of faeces by stripping. Apparent digestibility coefficients of protein (ADC-CP) in the animal products ranged from 47% for 60FMC to a high of 70% for fish solubles. ADC-CPs for animal products were not different across products. Blood meal, poultry by-product meal, Pro-Pak 60, Pro-Pak 65, and ProCon had intermediate ADC-CPs of 63, 55, 63, 57 and 52%, respectively. ADC-CP in plant feedstuffs ranged from 43% for canola meal to 80% for peanut meal. Brewer's yeast, canola meal, and sunflower meal had intermediate ADC-CPs at 54, 43 and 69%, respectively. Apparent amino acid availability coefficients were variable across animal products and did not necessarily correlate to the ADC-CPs for a given feedstuff. Isoleucine availability was low in blood meal at 38% compared with 59% or better for the remaining amino acids. Lysine, tyrosine and phenylalanine availability from fish solubles was low at 31, 35 and 44%, respectively. Amino acid availability from Pro-Pak 60 was consistently higher across all amino acids for the animal products and blends tested. Of the plant products tested, peanut meal was the best performing feedstuff relative to amino acid availability.

Channel catfish virus (CCV) disease is an acute haemorrhagic disease in juvenile channel catfish (Ictalurus punctatus). While fish that survive primary CCV infection are suspected of being carriers of CCV, little is known concerning CCV latency. In this report, fingerling catfish were infected with CCV by experimental immersion challenge. Infected fish displayed clinical signs of CCV disease, but 22% of infected fish survived the acute disease. At 140 days post-infection, PCR analysis detected CCV DNA in the blood, brain, intestines, kidney, liver and peripheral blood leukocytes of latently infected fish. Further analysis indicated the CCV genome may exist as circular or concatemeric DNA during virus latency. This study, employing an experimental model of CCV disease, confirms that CCV establishes a latent infection of channel catfish.

The free-living infective theront of Ichthyophthirius multifiliis historically has been thought to be the only stage susceptible to treatment. Here we introduce a technique to determine the toxicity of compounds to the newly released tomont, the encysted tomont and the developing tomites within the tomont that emerge as theronts. The toxicity of Wofasteril E400 (40% peracetic acid, PAA) to free-living forms of I. multifiliis was determined shortly after tomonts were physically removed from the surface of the fish and at 2.5 and 24 h after removal. Results indicate that 0.6 to 0.9 mg l(-1) PAA killed 39 to 82% of the newly released tomonts within 48 h when treated immediately. In a second experiment, tomonts were allowed to settle for 2.5 h after sampling from the skin and then treated for 12 h; concentrations > or =0.5 mg l(-1) PAA produced significantly fewer theronts than the controls. In a third experiment, encysted tomonts that were exposed to PAA 24 h after sampling from the skin and treated for 2 or 4 h produced a variable amount of theronts, but the concentrations tested (0.5 to 3.0 mg l(-1)) did not halt theront production. This research demonstrates that encysted I. multifiliis are less susceptible to chemical treatments.

A feeding trial was conducted in a closed system with Nile tilapia, Oreochromis niloticus, juveniles (mean initial weight, 2.66 g) to examine total replacement of menhaden fish meal (FM) with distiller's dried grains with solubles (DDGS), which had been used as substrate for the production of black soldier fly larvae, Hermetia illucens, in combination with soybean meal (SBM) and poultry by-product meal (PBM), with or without supplementation of the amino acids (AA) DL-methionine (Met), L-lysine (Lys) and a commercial non-amylaceous polysaccharide enzyme (Enz) product. Fish were fed seven isoenergetic [available energy (AE) = 4.0 kcal g−1 of diet] and isonitrogenous (350 g kg−1 protein as-fed basis) practical diets formulated with equivalent digestible protein levels. Diet 1 was formulated to be similar to a commercial, high-quality, tilapia diet containing 200 g kg−1 FM. Diets 2–5 were formulated as a 2 × 2 factorial to replace FM with similar contributions from DDGS (45%), PBM (25%) and SBM (2.1–2.9%), but to differ in supplementation of AA and/or Enz preparation. Diets 6 and 7 were formulated to investigate the effects of a 2/3 and 1/3 reduction, respectively, in DDGS contribution to the replacement protein mix, with concomitant increases in SBM, with respect to diet 3, and were balanced with Lys and Met. After 6 weeks, growth responses were slightly attenuated (P ≤ 0.05) and average daily intake (ADI) and feed conversion ratio (FCR) were slightly higher in tilapia fed DDGS diets 2–5 compared to those of fish fed the FM control diet 1. Growth responses were not significantly affected by the presence or absence of AA or Enz (diets 2–5), or the level of DDGS (diets 3, 7 and 6). Whole-body proximate composition was not different among treatments. Amino acid profiles of fish fed DDGS diets were not significantly different from those of fish fed the FM control. Evidence of interaction between AA and Enz supplementation was detected in whole-body amino acid concentrations such that AA content was higher with AA or Enz addition alone, but lower when both were added to the diet. Results suggest that DDGS replacement of FM in tilapia diets can be substantial when diets are formulated on a digestible protein basis and DDGS is combined with highly digestible animal (PBM) and plant proteins (SBM).

The influence of carbohydrate level and complexity on in vitro hepatic glucose utilization and lipogenesis were determined in hybrid striped bass, Morone chrysops ♀ × Morone saxatilis ♂. Six isocaloric, isonitrogenous diets containing glucose, maltose, or dextrin at two different levels (200 or 400 g kg−1 diet) were fed to adult fish for 15 weeks. Liver explants were obtained at near-maximum postprandial glycaemic response and incubated with radioactive labelled substrates. Glycogen synthesis from [14C]glucose was not different among treatments and was less than 14CO2 formation. 14CO2 production increased as a function of carbohydrate level but was unrelated to carbohydrate complexity. There was no detectable conversion of [14C]glucose to lactate for any treatment. Rates of de novo lipogenesis from [1-14C]acetate were high in comparison to [U-14C]glucose or [9,10-3H]palmitate incorporation into liver lipids and differed in response to carbohydrate level and complexity. [9,10-3H]palmitate esterification was an order of magnitude less than glycogen and CO2 production but 4–10 times greater than [14C]glucose incorporation into liver lipids. Palmitate incorporation did not differ among treatments. Incorporation of [14C]glucose into liver lipids was higher in fish fed diets containing 400 g kg−1 carbohydrate. These data support the idea that glucose is not a major oxidative substrate in hybrid striped bass and indicate that the level of soluble carbohydrate should be limited to 200 g kg−1 diet or less for hybrid striped bass.