Thomas L. Welker

Genetic fingerprinting of Flavobacterium columnare isolates from cultured fish

Aims:  To evaluate the intraspecific diversity of the fish pathogen Flavobacterium columnare

Technique for Identifying Flavobacterium columnare Using Whole-Cell Fatty Acid Profiles

Abstract Isolates of Flavobacterium columnare (29 from diseased fish and three American Type Culture Collection cultures [ATCC 23463, 49512, 43622]) were identified by use of biochemical characteristics prior to generating whole-cell fatty acid profiles. The microbial identification system (MIS; Microbial ID, Newark, Delaware), a gas chromatography system, was used to generate the fatty acid profiles of F. columnare. The MIS contains databases of clinically and environmentally important bacteria that are represented by over 100 genera, including Flavobacterium spp. (F. aquatile [ATCC 11947] and F. mizutaii). Flavobacterium columnare is not included in the databases because it does not grow on standard media. Fatty acid profiles of F. columnare were generated with the CLIN40 protocol established by MIS after growth of the bacteria in modified Shieh broth. The fatty acid composition of F. columnare isolates determined by the CLIN40 method consisted of 10 major fatty acids (those present at levels > 1%): 11-...

Use of Probiotics in Diets of Tilapia

Aquaculture is one of the fastest growing sectors of agriculture globally. Production in freshwater and marine fisheries has plateaued, and the increasing demand for seafood and need for affordable protein sources in third world countries will ensure growth of aquaculture in the future. Tilapia are the second most cultured fish worldwide behind the carps, and even though they are easily cultured in a wide variety of environments and are relatively resistant to aquaculture stressors compared to other cultured finfish species, significant losses to disease still occur under intensive culture. Traditionally, antibiotics and other chemicals have been used to treat disease outbreaks in cultured fish species. However, the scope of approved application for most antibiotics is very narrow and concern over development of antibiotic resistant pathogens will further limit use in the future. The focus instead has turned to finding safe and effective means of preventing infectious diseases in cultured finfish, including tilapia. In recent years, there has been considerable interest in the use of probiotic bacteria added to diets to increase immunity as well as improve growth performance in fish. Little probiotic research has been conducted in tilapia, but of the research that has been performed, most has taken place within the last five years. Due to its apparent effectiveness in improving health and growth in tilapia, research and interest in probiotics is likely to continue, which will hopefully fill existing research gaps.

Relationship between dietary lipid source, oxidative stress, and the physiological response to stress in sub-yearling chinook salmon (Oncorhynchus tshawytscha)

Relationships between dietary lipid source, stress, and oxidative stress were examined in juvenile chinook salmon (Oncorhynchus tshawytscha). Four different experimental diets were used: menhaden oil (MHO; elevated 20:5n-3 and 22:6n-3), soybean oil (SBO; elevated 18:2n-6), linseed oil (LSO; elevated 18:3n-3), and a mixture of 55% linseed oil and 45% soybean oil (MIX; approximately equal levels of 18:2n-6 and 18:3n-3). Juvenile salmon (initial body weight of 16.0 g) were fed experimental diets for 12 weeks (early March to early June). At the end of feeding, fish subjected to a low-water stressor for 96 h had greater liver and brain lipid peroxidation compared to unstressed controls; peroxidation was not influenced by diet. Diet and stress affected plasma cortisol levels. Stressed fish fed SBO had the greatest cortisol concentrations, followed by MIX, MHO, and LSO (mean concentrations for the SBO and LSO diets differed significantly). The cortisol response to stress may have been influenced by the ratio of prostaglandin 1- and 2-series to prostaglandin 3-series precursor fatty acids provided by the different diets. The results of this study suggest a connection between the physiological response to stress, dietary lipid quality, and oxidative stress. This is the first evidence of such a relationship in fish.Abbreviations: AA - arachidonic acid; ACTH - adrenocorticotropin; BHT - butylated hydroxytoluene; BLPO - brain lipid peroxidation; dGLA - dihomo-γ-linolenic acid; DHA - docosahexanoic acid; EPA - eicosapentanoic acid; FER - feed efficiency ratio; FOX - ferrous oxidation-xylenol orange; GLA -γ-linolenic acid; LA - linoleic acid; LCO3 - long-chain n-3 polyunsaturated fatty acids; LLPO - liver lipid peroxidation; LN - linolenic acid; LPO - lipid peroxidation; LSO - linseed oil; MHO - menhaden oil; MIX - 55% linseed oil + 45% soybean oil; PC - plasma cortisol; PG - prostaglandin(s); PGE2- prostaglandin E2; PUFA - polyunsaturated fatty acid; SBO - soybean oil.

Effects of Yeast Oligosaccharide Diet Supplements on Growth and Disease Resistance in Juvenile Nile Tilapia, Oreochromis niloticus

Commercially available yeast and yeast subcomponents consisting mainly of β-glucan or oligosaccharide feed additives were added to diets of juvenile (12–18g) Nile tilapia (Oreochromis niloticus) at rates recommended by suppliers. Three experiments were conducted following a basic protocol with varied rates of supplementation, duration of feeding, and stocking densities. Experimental diets were fed twice daily to apparent satiation for a period of two or four weeks, at the end of which feed consumption and weight gain were measured. Following the experimental feeding period, serum components, including protein and immunoglobulin concentrations, as well as lysozyme and complement activities, were measured. A disease challenge was conducted with pathogenic isolates of Streptococcus iniae or Edwardsiella tarda. Weight gains were not significantly different in fish fed the supplemented diets when compared to the control diet. There were significant differences in fed intake within individual experiments; however, this effect was not consistent in all three experiments. Overall feed efficiency was not significantly affected by diet. There were no differences in serum components of fish sampled at two or four weeks. Fish fed the experimental diets did not have lower mortality or morbidity after disease challenge compared to fish fed the control diets. Specific antibody against S. iniae or E. tarda measured by ELISA did not reveal differences in the fish surviving the challenge. We conclude that the incorporation of these commercial yeast component products into the diet of juvenile Nile tilapia at these rates and for these feeding periods had no effect on growth, serum components, antibody responses, or survival following S. iniae or E. tarda infection.

Effect of Buffered and Unbuffered Tricaine Methanesulfonate (MS-222) at Different Concentrations on the Stress Responses of Channel Catfish, Ictalurus punctatus Rafinesque

ABSTRACT The effects of four concentrations (0, 90,120, and 180 mg/L) of the anesthetic tricaine methanesulfonate (MS-222) (buffered and unbuffered with sodium bicarbonate) were evaluated on anesthetization efficacy and stress responses of juvenile channel catfish, Ictalurus punctatus Rafinesque. Buffered MS-222 treatments were neutralized with sodium bicarbonate to bring the pH of exposure water to that of rearing water (pH ∼7.0). Fish were exposed to MS-222 treatments for 10 minutes after reaching stage 3 anesthetization, or for 10 minutes only for the control treatment (0 mg/L MS-222). Blood was sampled from fish at the end of the 10 minute exposure period and after 30,60,120,240, and 480 minutes recovery in aquaria to measure blood glucose and plasma cortisol and osmolality. With increasing MS-222 concentration, there were significant decreases in pH (7.0 to 5.7) and increases in osmolality (40 to 63 mOsm/kg) in unbuffered water, while osmolality (43 to 69 mOsm/kg), but not pH, were significantly different among the treatments in buffered water. As expected, anesthesia induction time was reduced and recovery time was increased as MS-222 exposure concentration increased. Buffering of exposure water had no effect on anesthetization induction or recovery. Sampling time and MS-222 concentration, but not buffering or pH, had significant effects on the stress responses. Although anesthetization reduced the cortisol response to handling, plasma cortisol concentrations increased with increasing MS-222 concentration regardless of buffering, suggesting an anesthesia effect that was unrelated to MS-222 acidification of exposure water. The blood glucose response also increased with increasing MS-222 concentration; however, glucose concentrations, unlike cortisol, were lowest in handled, non-anesthetized fish, which suggests that stress-related hyperglycemia may not be solely under cortisol control. We determined 90 mg/L MS-222 to be an effective dose for fingerling channel catfish, which provided a moderate rate of anesthesia without significantly exacerbating the cortisol response to handling.

Oxidative Stress in Migrating Spring Chinook Salmon Smolts of Hatchery Origin: Changes in Vitamin E and Lipid Peroxidation

Abstract Polar lipid peroxidation (LPO), a measure of oxidative damage to membrane lipids, and concentrations of the antioxidant vitamin E were determined for kidney and liver tissues of Chinook salmon Oncorhynchus tshawytscha sampled before release from three hatcheries in the Snake River basin, Idaho, and from juvenile fish bypass systems at several dams in the Columbia– Snake River federal hydropower system. Oxidative stress, as indicated by LPO, significantly increased in migrating juveniles after they left the hatchery in each of the study years (1999 and 2000). The largest increase in liver LPO occurred between the hatcheries and Lower Granite Dam (the first dam encountered by migrating fish) with little or no additional change as the fish migrated through the hydropower system. Kidney LPO, on the other hand, continued to increase as the fish migrated to lower Columbia River dams 348–461 km downstream. Levels of vitamin E were inversely correlated with LPO. Postrelease decreases in vitamin E were si...