Thomas Welker

Growth Performance and Resistance to Streptococcus iniae of Juvenile Nile Tilapia (Oreochromis niloticus) Fed Diets Supplemented with GroBiotic-A and Brewtech Dried Brewers Yeast

This study was conducted to evaluate the effect of dietary levels of Brewtech dried brewers yeast (BY) and GroBiotic-A (GB) on growth performance, proximate body composition, immune response, and resistance of juvenile Nile tilapia to Streptococcus iniae challenge. A practical basal (control) diet formulated to contain approximately 32% crude protein and 6% lipid was supplemented with 1% and 2% of BY or GB. Each diet was fed to Nile tilapia in quadruplicate aquaria for 12 weeks. Weight gain, feed intake, survival, and whole body proximate composition of fish were not significantly affected by dietary treatments. Serum total protein, total immunoglobulin, lysozyme, and agglutinating antibody titer to S. iniae were not significantly affected by dietary supplementation of BY or GB. However, serum haemolytic complement activity (SH50) of fish fed 1% BY was significantly higher than those of fish fed the control diet and diets supplemented with 2% BY or GB. Cumulative mortality of fish 20 days post-challenge with S. iniae was unaffected by dietary treatments. However, fish fed diets supplemented with 1% BY and 2% BY or GB had substantially reduced and earlier cessation of mortality.

Food Shortage Causes Differential Effects on Body Composition and Tissue-Specific Gene Expression in Salmon Modified for Increased Growth Hormone Production

Growth hormone (GH) transgenic salmon possesses markedly increased metabolic rate, appetite, and feed conversion efficiency, as well as an increased ability to compete for food resources. Thus, the ability of GH-transgenic fish to withstand periods of food deprivation as occurs in nature is potentially different than that of nontransgenic fish. However, the physiological and genetic effects of transgenic GH production over long periods of food deprivation remain largely unknown. Here, GH-transgenic coho salmon (Oncorhynchus kisutch) and nontransgenic, wild-type coho salmon were subjected to a 3-month food deprivation trial, during which time performance characteristics related to growth were measured along with proximate compositions. To examine potential genetic effects of GH-transgenesis on long-term food deprivation, a group of genes related to muscle development and liver metabolism was selected for quantitative PCR analysis. Results showed that GH-transgenic fish lose weight at an increased rate compared to wild-type even though proximate compositions remained relatively similar between the groups. A total of nine genes related to muscle physiology (cathepsin, cee, insulin-like growth factor, myostatin, murf-1, myosin, myogenin, proteasome delta, tumor necrosis factor) and five genes related to liver metabolism (carnitine palmitoyltransferase, fatty acid synthase, glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, glucokinase) were shown to be differentially regulated between GH-transgenic and wild-type coho salmon over time. These genetic and physiological responses assist in identifying differences between GH-transgenic and wild-type salmon in relation to fitness effects arising from elevated growth hormone during periods of long-term food shortage.

Effect of Feeding Duration of Sodium Chloride-Containing Diets on Growth Performance and Some Osmoregulatory Parameters of Nile Tilapia, Oreochromis niloticus, After Transfer to Water of Different Salinities

ABSTRACT Two feeding experiments were conducted to evaluate the effect of feeding duration of dietary salt (NaCl or S) on hematocrit, blood glucose, serum osmolality, and cortisol of Nile tilapia, Oreochromis niloticus, acclimated for various time periods to salt water (SW) of different salinities (three-factor experiment). Quadruplicate groups of fish averaging 5.52 ±0.13 g (Experiment I) and 10.04 ±0.19 g (Experiment II) were fed to apparent satiation twice daily with the following four feeding regimens: feeding the control diet (C) for 6 weeks (6-wk C); feeding the 6% NaCl (S) diet for 6 weeks (6-wk S); feeding the C diet for 2 weeks; and the S diet for 4 weeks (2-wk C +4-wk S); and feeding the C diet for 4 weeks and S diet for 2 weeks (4-wk C +2-wk S). At the end of week 6, fish in each aquarium were weighed for growth measurement. Fish from each replicate aquarium in Experiment I were transferred to SW at 0, 15 and 30 ppt whereas those from Experiment II were transferred to SW at 0, 10, and 20 ppt. Hematocrit (Experiment II only), blood glucose, serum osmolality, and cortisol were determined at 48 and 96 hours, and 0, 6, 12, 24, and 48 hours for Experiments I and II, respectively, after transfer to SW. In both experiments, weight gain after 6 weeks of feeding did not differ (P> 0.05) among treatments, although all fish in the treatment receiving the NaCl-containing diet had consistently higher weight gain than those fed the C diet. Dry matter diet intake and survival were similar in both studies. Feed efficiency, however, was significantly different only in Experiment I, and was consistently better for the groups that were fed the NaCl-containing diet. All fish transferred to 30 ppt salinity died within 8 hours. No mortality occurred in fish transferred to 0, 10, 15, or 20 ppt salinity. Feeding dietary salt had no effect on blood glucose and hematocrit levels in either study. Serum osmolality of fish in Experiment I decreased in fish fed dietary salt, but the differences were not always significant. This value was similar among fish fed dietary salt in Experiment II. In both experiments, blood glucose and serum osmolality significantly (P< 0.05) increased, whereas hematocrit decreased with increasing water salinity. Duration of exposure to SW also significantly (P< 0.05) increased blood glucose levels but decreased hematocrit values. Duration of SW exposure had no effect on serum osmolality. The interaction between dietary salt and water salinity; water salinity and exposure time; and dietary salt and exposure time had no effect on hematological and serological values in both experiments, except blood glucose and plasma osmolality and cortisol in Experiment II were significantly (P< 0.05) affected by water salinity and exposure time. The interaction between the three main factors had no effect on measured hematological parameters.

Effects of feed processing method (extrusion and expansion-compression pelleting) on water quality and growth of rainbow trout in a commercial setting

ABSTRACT To determine the effects of feed processing method (extrusion or expansion followed by compression pelleting) on feed physicochemical characteristics, fecal stability, water quality, and growth performance in rainbow trout, three types of feed pellets (expanded sinking [EpS], extruded sinking [ExS], extruded floating [ExF]) were prepared, analyzed, and fed to juvenile rainbow trout (initial weight = 285.8 ± 15.2 g) at three feeding rates based on feeding rate curves developed at Snake River Farm (Buhl, Idaho, USA) (median rates [%BW] for feeding rate 1: 0.85; feeding rate 2: 0.95; feeding rate 3: 1.05) for 124 days. Results showed that all feeds had similar chemical composition, but the degree of starch gelatinization (as % of starch) was significantly higher in ExS (90.01 ± 0.26) and ExF (84.82 ± 0.63) than in the EpS (9.09 ± 0.41) feed, which led to extruded feeds having much higher water stability, fecal durability, and lower phosphorus discharge. The ExF feed produced better growth (% increase; 154.4 ± 18.5) and feed conversion (1.06 ± 0.06) compared to EpS (126.3 ± 12.4 and 1.26 ± 0.14) and ExS (121.7 ± 7.8 and 1.22 ± 0.04) in rainbow trout. Growth (% increase) improved as feeding rate increased (feeding rate 1: 125.6 ± 10.3; feeding rate 2: 140.8 ± 16.0), but further improvements were not observed at the highest feeding rate (feeding rate 3: 135.9 ± 22.8). The present study is the first to show that the extrusion process not only produces pellets having better quality than the expansion-compressed pelleting method but also improves fecal size and durability in water, and therefore, use of extruded feeds has the potential to improve waste collection and removal and reduce contribution to pollution in effluent.