Donald H. Lewis

Streptococcus iniae Associated with Mortality of Tilapia nilotica × T. aurea Hybrids

Abstract The cause of an ongoing mortality of hybrid tilapias Tilapia nilotica × T. aurea in a Texas fish farm was a biotype of Streptococcus iniae. Identification was based upon classical biochemical and physiological analysis as well as ribosomal RNA gene sequencing. The causative agent, a β-hemolytic Streptococcus species, grew better at 37°C than at 10, 25, or 40°C, and its growth was inhibited at pH 9.6, in 6.5% NaCl, and in 40% bile. The bacterium was resistant to ampicillin and furazolidone but was susceptible to several antibiotics including tetracycline, oxytetracycline, and sulfadimethoxine-ormetoprim (5:1). This is the first record of this bacterial species affecting fish in the USA. External signs of disease in tilapia were loss of orientation, exophthalmia, corneal opacity, and petechia around the mouth, anus, and proximal margins of the pectoral fins. Internally, fluid accumulation in the peritoneal cavity and enlargement of the liver, spleen, and kidney were observed.

Epizootiological aspects of Streptococcus iniae affecting tilapia in Texas

Abstract Some epizootiological aspects of a bacterial septicemia of hybrid tilapia (Tilapia nilotica X T. aurea) caused by a biotype of Streptococcus iniae were investigated. Bacterial growth in Brain Heart Infusion broth was detected at 10, 25, 35 and 45 °C, between pH 5.5–8.5, and at salinities of up to 30 ppt. After suspension of the bacteria in distilled water, viable cocci were recovered for up to 5 days at 5 °C and

Instantaneous Reproductive Effort in Female American Oysters, Crassostrea virginica, Measured by a New Immunoprecipitation Assay

An immunoprecipitation assay was developed for measuring instantaneous reproductive effort in female American oysters, Crassostrea virginica. Oysters were injected with 14C-leucine and incubated in situ for 1 to 30 h periodically throughout the annual gametogenic cycle. Gonadal protein labeled with 14C-leucine was precipitated from an oyster homogenate with rabbit anti-oyster egg IgG as the primary antibody. Antibody-oyster egg protein complex was further purified by immunoadsorption with staphylococcal protein A cell suspension. The quantity of oyster eggs was determined by single-ring immunodiffusion. A mathematical model was developed to calculate the instantaneous reproductive rate of oysters and to estimate the number of days required from the initiation of gonadal development to spawning. The oyster population was lightly to moderately infected with a protozoan parasite, Perkinsus marinus. A negative correlation between the intensity of infection and the rate of gonadal production suggests that P. marinus retards the rate of gamete development. The seasonal cycle of gamete production determined by direct measurements of egg protein production was not equivalent to that determined by standard gonadal-somatic index (GSI), except at the most basic level. GSI was highest during the spring spawning peak, but the rate of gamete production was highest in the fall. Accordingly, the two measurements, rate versus standing crop (volume of gonad), reveal a substantially different picture about the details of the spawning season. Estimates of the time required to reach spawning condition ranged from several weeks to 1 or 2 months; these values agree with published estimates derived from less direct methods. Direct rate measurements thus seem to accurately reflect the true rate at which gametic tissue is produced in the field. A positive correlation between oyster size and the estimated days to spawn suggests that larger oysters require longer to prepare to spawn. Furthermore, the range in observed somatic and gametic growth emphasizes the conservatism of somatic growth and the volatility of gonadal growth that is borne out by the results of population dynamics models of oysters.

Feedstock storage, handling and processing

Abstract This paper is a review of the technology and research covering components of a methane from biomass system between the field and the digester. It deals primarily with sorghum as a feedstock and focuses on research conducted by the Texas Agricultural Experiment Station. Subjects included in this paper are harvesting, hay storage, ensiling, materials handling, pumping and hydraulic characteristics, hydraulic conductivity, pressure/density relationship, and biological pretreatment. This paper is not a comprehensive design manual; however, design equations and coefficients for sorghum are presented, where available, along with references describing the development and application of design models.

Interaction of bacteria and male reproductive system blackening disease of captive Penaeus setiferus

Abstract The genital apparatus of male penaeid shrimp, Penaeus setiferus, blackens with resulting detrimental effects on mating for production of larvae when animals are kept in controlled maturation/reproduction situations. A progressive, melanized condition of the male reproductive tract was shown to be associated with bacterial infection. At least three different species (Vibrio alginolyticus, Pseudomonas putrefaciens, and an unclassified strain), were isolated from damaged tissues and successfully developed the same signs in challenge experiments. It is suggested that the condition could be a progressive syndrome with bacterial invasion perhaps only in the advanced stages, or that more than one etiology may be involved in deterioration and blackening of the P. setiferus reproductive system.

Response of Young Channel Catfish to Diets Containing Purified Fatty Acids

Abstract Nine-gram channel catfish Ictalurus punctatus fed 10 weeks on diets containing ethyl esters of stearic, oleic, linoleic, and linolenic acids did not demonstrate a strong requirement for linolenic-family fatty acids. Growth was inhibited when diets contained 1% or 2% linolenic acid (by weight) but no oleic or linoleic acids. If channel catfish require dietary linolenic acid, it is at a concentration below 1%. The previous view that poor growth of channel catfish on diets supplemented with vegetable oils was due to high levels of linoleic acid appears to have been incorrect. Soybean oil, and other vegetable oils, contain several percent linolenic acid. Growth depression may occur when such oils are utilized at levels of 5 to 10% of the diet. Proximate analyses revealed that fish on all diets had similar body compositions of lipid, protein, and moisture. Among the fatty acids, dietary linoleic and linolenic acid were stored and fish became depleted in those acids when they were excluded from the die...

Lymphocystis in Red Drum

Abstract This report documents natural infection and experimental transmission of lymphocystis in red drum Sciaenops ocellatus. Lymphocystis was a chronic problem in a commercial red drum production facility in Texas during 1993–1994. Electron microscopy of lesions and infected cell cultures revealed an icosohedral virus 220–230 nm in diameter. The virus was experimentally transmitted by intramuscular injection and oral administration, with the development of lesions restricted to fins and adjacent tissues. Cell culture of the virus yielded large numbers of incomplete particles, which might account for variations in experimental transmission of lymphocystis.

Characterization of a Virus Associated with Head and Lateral Line Erosion Syndrome in Marine Angelfish

Abstract The morphological and biophysical characteristics were determined for a previously unreported angelfish reovirus isolated from a moribund angelfish Pomacanthus semicirculatus exhibiting clinical signs associated with head and lateral line erosion syndrome. Viral particles were nonenveloped, possessed a segmented double-stranded RNA genome enclosed by a double nucleocapsid, and were resistant to inactivation by ether and low pH. Electrophoretic and serologic characteristics of this viral agent were compared with those of other aquatic reoviruses isolated from different fish hosts (chum salmon Oncorhynchus keta, golden shiner Notemigonus crysoleucas, and channel catfish Ictalurus punctatus). Based upon these findings, molecular weights were estimated for the 11 genomic segments (0.34–2.4 × 106) and some of the major structural viral polypeptides (34.4–137.0 × 103).

Immune Hypersensitivity in Intensively Cultured Tilapia Species

Abstract Tilapia mossambica maintained at high densities in an intensive-culture tank system displayed hypersensitivity to a component present in mucus and culture water. The component induced cutaneous anaphylactic reactions in T. mossambica and three other Tilapia species, but did not affect Ictalurus punctatus. Gel filtration studies revealed the component to be high molecular weight (larger than 8 × 105 daltons) which electrophoretically migrated as a beta globulin. The component recovered from tank water of T. mossambica was not found in T. aurea tank water or in the incoming water. Tilapia mossambica experience higher mortality due to this autoimmune reaction, which limits the density at which this species can be stocked. Because the compound affects several species within the Tilapia genus, its effects should be considered when tilapias are stocked in fish culture operations.

Aggregation of penaeid shrimp larvae due to microbial epibionts

Abstract Pseudomonas piscicida, Aeromonas formicans and Flavobacteria sp. were involved in aggregation of hatchery reared Penaeus stylirostris larvae. Aggregation was experimentally reproduced with pure cultures of these organisms at densities of 10 4 cells per ml. Adding at least 3 μg/ml gentamycin, 10 μg/ml nalidixic acid, 0.1 μg/ml acridine or Cutrine Plus ® ∗ into test suspensions prevented aggregation of the shrimp larvae.