J. Alejandro Buentello

Effects of water temperature and dissolved oxygen on daily feed consumption, feed utilization and growth of channel catfish (Ictalurus punctatus)

Abstract Feed intake (FI), feed efficiency (FE), protein efficiency ratio (PER) and weight gain (WG) of juvenile channel catfish initially weighing 15.0±0.23 g (10–12 cm initial total length) were evaluated under three regimes of time-varying water temperature (mean daily water temperature for Stoneville, MS, USA; mean +3; and, mean −3°C) and three of dissolved oxygen (DO; 100, 70 and 30% air saturation, at each temperature). Two independent experiments lasting 6 and 8 weeks, respectively, simulated spring and fall temperature and photoperiod patterns. Temperature–oxygen regimes were applied to randomly assigned duplicate 110-l aquaria with individual biofilters. Fish were fed once daily, to slight excess, a commercial catfish floating feed. After 45 min, uneaten feed was collected, dried and weighed; then FI was calculated by difference. Fish in each aquarium were weighed collectively, biweekly. In both experiments higher temperatures and higher DO levels produced increased feed consumption. A multivariate regression model was fitted to the data to describe the combined effects of temperature and DO on FI. There was a progressive reduction in FI as DO declined from 100 to 30% air saturation. In both trials weight gain was higher for fish held 3°C above the mean water temperature at 100% air saturation values of DO; whereas, the lowest values of WG were obtained for fish held at 30% air saturation and 3°C below the mean water temperature. Weight gain increased with temperature, with maximum rates reached at 27.1°C with DO equivalent to 100% air saturation. In contrast, when DO was 30% air saturation, growth rates plateaued as ambient temperature exceeded 22.8°C. This model will assist in optimization of feeding practices in channel catfish aquaculture.

The dietary arginine requirement of channel catfish (Ictalurus punctatus) is influenced by endogenous synthesis of arginine from glutamic acid

Previous studies with young mammals have established that arginine synthesis from glutamate-derived citrulline can be a major endogenous source of arginine. Therefore, an experiment was conducted to re-assess the dietary arginine requirement of juvenile channel catfish and to determine the metabolic effects of including glutamate or glycine to maintain isonitrogenous levels among diets. Two sets of diets were formulated to contain 24 g crude protein/100 g dry weight from casein/gelatin and crystalline amino acids with arginine supplementation in 0.5 increments from 0.5 to 2.0 g/100 g diet. Amino acid nitrogen was maintained equal, within sets, by replacing arginine with aspartate and either glutamate or glycine. Each diet was fed to apparent satiation to triplicate groups of 12 fish initially averaging 11.4 g/fish for 8 weeks. Weight gain (WG), feed efficiency (FE), protein efficiency ratio (PER), protein retention (PR) and survival were significantly (P < 0.05) affected by arginine. At the suboptimal level of dietary arginine, glutamate appeared to contribute arginine through internally derived citrulline based on increased plasma citrulline and arginine concentrations. WG and plasma amino acid concentrations of fish fed diets with glycine suggested that it does not serve as a precursor for citrulline. Based on WG and FE, juvenile channel catfish were found to require arginine at 3.3% to 3.8% of dietary protein, when glutamate was included in the diet. The requirement estimate was 33% higher when glycine replaced glutamate in the diet and was similar to the previously determined arginine requirement of channel catfish at 4.3 g/100 g of dietary protein. These results strongly suggest that dietary glutamate is used for endogenous synthesis of arginine in channel catfish, especially when arginine is deficient in the diet.

Nitric oxide production in activated macrophages from channel catfish (Ictalurus punctatus): influence of dietary arginine and culture media

Abstract Recent studies have demonstrated that fish macrophages produce NO which plays a significant role in macrophage killing of microorganisms. The sole precursor for NO is the amino acid arginine. To elucidate the mechanisms which regulate NO production in these cells we examined the effects of increasing levels of dietary arginine on the induction of NO synthesis in macrophages from channel catfish. Additionally, the effects of four different media compositions in 96-h cell incubations were evaluated. A 9-week feeding trial was conducted to ascertain the effects of different dietary arginine levels on NO production in peritoneal macrophages. Diets were formulated to contain 24% crude protein from casein and gelatin, and supplemented with crystalline l -amino acids to meet the amino acid requirements of channel catfish. Four isocaloric dietary treatments provided arginine at either 0.52, 1.00, 1.50 or 2.00% of diet. The total amount of amino acid nitrogen was maintained equal by replacing arginine with either glutamate or glycine. Diets were fed to apparent satiation to triplicate groups of channel catfish initially averaging 11.4 g/fish. At the end of the trial, peritoneal macrophages were elicited by injecting 1 mg lipopolysaccharide (LPS)/kg body weight. Macrophages were collected, evaluated for viability and incubated in 24-well cell culture plates for 96 h, using Krebs–Henseleit buffer with 0.5% bovine serum albumin as standard media. Arginine, citrulline, arginine plus glutamine or arginine plus N G -monomethy- l -arginine ( N G MMA) were added to the culture medium to achieve a 0.5-mM concentration. Nitrate and nitrite production were measured spectrophotometrically as indicators of NO generation. Results indicate that cultured catfish macrophages synthesize NO in response to bacterial LPS at different rates depending upon composition of culture media. NO production was increased when arginine, citrulline and arginine plus glutamine were used as substrates; arginine plus glutamine had the most significant increase (5-fold). Macrophage NO generation was inhibited by N G MMA, suggesting an arginine-dependent metabolic pathway for production of NO in channel catfish. Dietary arginine levels did not correlate significantly with the amount of NO produced. In vivo, however, plasma arginine may partially regulate the intracellular availability of arginine and thus prolong the production of NO by macrophages. This would become physiologically relevant as disease-challenged fish deplete arginine from blood. Further research to assess the effects of dietary arginine on channel catfish immunocompetence in vivo appears warranted.

Effects of Elevated Dietary Arginine on Resistance of Channel Catfish to Exposure to Edwardsiella ictaluri

Abstract An experiment was conducted to assess the effects of elevated dietary arginine on infection resistance to Edwardsiella ictaluri by juvenile channel catfish Ictalurus punctatus. Healthy channel catfish fingerlings were fed casein- and gelatin-based purified diets containing 28% crude protein and supplemented with crystalline L-arginine at 0.5, 1, 2, or 4% of the diet. An intact-protein diet containing 1.3% arginine also was included to investigate the effects of amino acid form (crystalline free amino acids versus intact protein). Each diet was fed to apparent satiation to triplicate groups of fish for 2 weeks. Subsequently, fish were exposed by immersion (1.3 × 108 colony-forming units/mL) to a virulent strain of E. ictaluri. Morbidity, mortality, and cause of death were recorded during a 21-d period. Plasma amino acid concentrations (14 h postprandial) 1 d before and 1 d after the bacterial exposure were analyzed via high-performance liquid chromatography. The dietary concentration of L-arginine...

A novel approach for assessing protein synthesis in channel catfish, Ictalurus punctatus

A comprehensive understanding of animal growth requires adequate knowledge of protein synthesis (PS), which in fish, has traditionally been determined by the flooding dose method. However, this procedure is limited to short-term assessments and may not accurately describe fish growth over extended periods of time. Since deuterium oxide ((2)H(2)O) has been used to non-invasively quantify PS in mammals over short- and long-term periods, we aimed at determining if (2)H(2)O could also be used to measure PS in channel catfish. Fish were stocked in a 40-L aquarium with approximately 4% (2)H(2)O and sampled at 4, 8 and 24h (n=6 at each time period) to determine (2)H-labeling of body water (plasma), as well as protein-free and protein-bound (2)H-labeled alanine. The labeling of body water reflected that of aquarium water and the labeling of protein-free alanine remained constant over 24h and was approximately 3.8 times greater than that of body water. By measuring (2)H-labeled alanine incorporation after 24h of (2)H(2)O exposure we were able to calculate a rate of PS: 0.04+/-0.01% h(-1). These results demonstrate that PS in fish can be effectively measured using (2)H(2)O and, because this method yields integrative measures of PS, is relatively inexpensive and accounts for perturbations such as feeding, it is a novel and practical assessment option.

Preliminary Observations on the Effects of Water Hardness on Free Taurine and Other Amino Acids in Plasma and Muscle of Channel Catfish

Abstract An interesting metabolic adjustment that fish make in their adaptation to a particular environment concerns the maintenance of the proper osmotic balance in their tissues. Free amino acids can be important isosmotic regulators; they contribute to intra- and extracellular fluid osmolality and are important in cell volume regulation. For this reason, a laboratory experiment was conducted to evaluate the effects of water ionic composition on the level of free amino acids in the plasma and muscles of juvenile channel catfish Ictalurus punctatus. Duplicate groups of fish were fed a commercial diet (40% crude protein) twice daily to apparent satiation. Fish were held under two different regimes of water hardness, 17.9 and 407 mg/L as CaCO3, which were considered soft and hard water, respectively. Blood and muscle samples were obtained from fish at the start and termination of the 4-week experiment. Mean plasma osmolarity was 294 and 273 mmol/kg for fish reared in hard and soft water, respectively. Anal...

Phosphorus Availability in Low-Phytate Mutant Varieties of Barley: Digestibility Studies with Channel Catfish and Red Drum

Abstract About 70% of the phosphorus in plant feedstuffs is typically in the form of organic phytates, but molecular phytogenetic techniques allow the development of variant seed forms that are capable of storing most of it in an inorganic form. In response to concerns over excessive phosphorus discharges from uneaten or unassimilated aquaculture feeds, two independent digestibility trials were conducted to evaluate the suitability of single-gene, low-phytic-acid mutations of barley Hordeum vulgare as feedstuffs for channel catfish Ictalurus punctatus and red drum Sciaenops ocellatus. Five isonitrogenous and isocaloric diets containing five different barley variants plus one reference diet (RD) were independently evaluated with each species. The RD for catfish contained 30% menhaden Brevoortia tyranus fish meal and 30% soybean meal, whereas the red drum RD included 48% lyophilized red drum muscle meal as the sole protein source. Each experimental diet was formulated so that a barley mutant replaced 30% of...