Molecular characteristics of an immobilization antigen gene of the fish-parasitic protozoan Ichthyophthirius multifiliis strain ARS-6

Ichthyophthirius multifiliis (Ich), a ciliated protozoan parasite of fish, expresses surface antigens (i-antigens), which react with host antibodies that render them immobile. The nucleotide sequence of an i-antigen gene of I. multifiliis strain ARS-6 was deduced. The predicted protein of 47 493 Da is comprised of 460 amino acids (aa's) arranged into five imperfect repeats with periodic cysteine residues with the structure: CX₍₁₉₎₂₀CX₂CX₁₆₋₂₇CX₂CX₂₀₍₂₁₎CX₃. The N-terminal aa's typify a signal peptide motif while a stretch of C-terminal aa's resemble a glycosyl–phosphatidyl–inositol (GPI)-anchor addition site. The degree of deduced i-antigen aa sequence identity of strain ARS-6 (GenBank accession # ACH87654 and # ACH95659) with other I. multifiliis i-antigen sequences present in GenBank ranges from 99% to 36% identity with 52 kDa i-antigens of I. multifiliis strain G5 (accession #s AAK94941 and AAK01661 respectively). Immunoblot analysis of i-antigens following exposure of I. multifiliis theronts to catfish anti- I. multifiliis immune serum did not show any appreciable alteration in i-antigen expression. The mechanism that regulates i-antigen expression in I. multifiliis remains a puzzling question.     

Efficacy of an experimentally inactivated Streptococcus agalactiae vaccine in Nile tilapia (Oreochromis niloticus) reared in Brazil

Tilapia aquaculture is one of the fastest‐growing segments of fish production in Brazil. Nile tilapia (Oreochromis niloticus) is largely cultivated in the state of Parana, where Streptococcus agalactiae is the cause of severe disease outbreaks. The objective of this paper was to evaluate an inactivated S. agalactiae vaccine in tilapia for the control of streptococcal disease outbreaks. Tilapia, weighing approximately 20 g each, were intraperitoneally (i.p.) inoculated with 0.1 mL of the vaccine at a dose of 2.0 × 10⁸ colony‐forming unit (CFU) mL^?1. One group of tilapia (treatment 1) received one vaccine dose, and the other group of tilapia (treatment 2) received two doses, with an interval of 21 days. The control group was i.p. inoculated with 0.1 mL tryptic soy broth fish^?1. Immunized and control tilapia were i.p. challenged with 0.1 mL of 3.0 × 10⁷ CFU mL^?1 at 30 days post vaccination. The fish were monitored daily for disease signs and for mortality for 16 days post challenge. A statistically significant difference (P=0.0045) was found between the mortality of treatments 1 and 2. The value of relative per cent of survival of 83.6% and 96.4%, respectively, indicate that this vaccine was efficient in Nile tilapia.     

The macrophage chemotactic activity of Edwardsiella tarda extracellular products

The chemoattractant capabilities of Edwardsiella tarda extracellular products (ECP) were investigated from two isolates, the virulent FL6-60 parent and less virulent RET-04 mutant. Chemotaxis and chemokinesis were assayed in vitro using blind well chambers with peritoneal macrophages obtained from Nile tilapia, Oreochromis niloticus, 5 days following squalene injection. Non-purified ECP derived from both isolates stimulated predominantly chemokinetic migration of macrophages. Additionally, the ECP were semi-purified by high pressure liquid chromatography. The FL6-60 parent ECP yielded higher molecular weight components than did the ECP from the RET-04 mutant. The chemotactic activity of the macrophages for both the FL6-60 parent and RET-04 mutant semi-purified ECP was increased over the non-purified ECP and overall migration was primarily chemotactic. Exposure to ECP derived from virulent and less virulent E. tarda isolates promoted chemokinetic movement of macrophages that may be involved in inflammatory responses of Nile tilapia to E. tarda infection.     

Evaluation of Distiller's Dried Grains with Solubles from Different Grain Sources as Dietary Protein for Hybrid Tilapia,Oreochromis niloticus (♀) × Oreochromis aureus (♂)

The effects of distiller's dried grains with solubles (DDGS) from different sources on growth performance, hematology, and immunity of hybrid tilapia, Oreochromis niloticus × Oreochromis aureus, were evaluated. Sex‐reversed, all‐male hybrid tilapia (3.72 ± 0.08 g initial weight) were fed diets in which 30% of protein in the control diet, supplied by a combination of soybean meal (SBM) and corn meal (CM) (SBM : CM ratio = 1.8), was replaced by wheat DDGS (WtDDGS), sorghum DDGS (SDDGS), whiskey DDGS (WkDDGS), or one of three corn DDGS (CDDGS 1–3) sources (control and six experimental diets) for 10 wk. Tilapia were stocked at 30 fish per aquaria (three aquaria per diet). Growth of tilapia fed diets containing DDGS sources was similar to or better than the control diet, and no nutritional deficiencies were observed. Tilapia fed the CDDGS 2 and 3 sources showed superior weight gain. Improved growth appeared to be caused by an increase in feed intake and not due to improvements in dietary nutritional value. Hematology and immunity were not affected by DDGS source. It is concluded that DDGS from all the sources examined can be included in the diet of juvenile hybrid tilapia at about 30% as a replacement of one‐third protein from SBM‐CM mixture without adverse effects.     

Growth,Body Fatty Acid Composition,Immune Response,and Resistance to Streptococcus iniae of Hybrid Tilapia,Oreochromis niloticus × Oreochromis aureus,Fed Diets Containing Various Levels of Linoleic and Linolenic Acids

The effects of dietary linoleic (LA) and linolenic acids (LN) on growth and immunity of all‐male hybrid tilapia, Oreochromis niloticus × Oreochromis aureus, were evaluated for 10 wk. Fish fed 0.12% LA + 0% LN had the lowest weight gain (WG) but was not significantly different from diets containing 0.5% LA or 0.40% LA + 1.0% LN. Fish fed 1% LA had the highest WG but did not differ from diets with 0.5% LA, 2.0% LA, 0.26% LA + 0.5% LN, 0.69% LA + 2.0% LN, or diets containing both LA and LN at 0.25, 0.5, and 1.0%. Feed intake, feed efficiency, and survival did not differ among treatments. Total body n‐6 fatty acids (FAs) increased with increasing dietary levels of n‐6. Total body n‐3 FAs also appeared to increase with increasing dietary n‐3 levels but peaked at 1% of diet. Dietary treatment had no effect on hematology, immune function, or survival to Streptococcus iniae. This study indicates that both LA and LN are dietary essential for growth of hybrid tilapia. Dietary LA alone can meet the essential FA requirement, and a level of 1.14% of diet is required for optimum growth.     

Protection against heterologous Streptococcus iniae isolates using a modified bacterin vaccine in Nile tilapia,Oreochromis niloticus (L.)

Streptococcus iniae is a significant pathogen impacting aquaculture production worldwide. The objectives of this study were to determine whether a developed modified S. iniae (ARS-98-60) bacterin vaccine is efficacious in Nile tilapia, Oreochromis niloticus (L.), against challenge with heterologous isolates from diverse geographical locations and to evaluate protein and antigenic variability among the isolates tested. Two groups of tilapia (approximately 5 g) were intraperitoneally (IP) vaccinated with 100 μL of the vaccine or sham vaccinated with 100 μL of sterile tryptic soy broth and held for 28 days. Fish were challenged with each isolate by IP injection of 2–3 × 10⁷ CFU per fish using calcein to mark fish prior to cohabitation for challenge. The results demonstrated significant protection against all challenge isolates, and relative percent survivals ranged from 79% to 100%. SDS–PAGE analysis of whole-cell lysate proteins from the S. iniae isolates demonstrated similar protein profiles between 10 and 31 kDa and variation in profiles between 35 and 100 kDa. Western blot analysis using antiserum from vaccinated fish (ARS-98-60) demonstrated shared immunogenic proteins among all isolates in the molecular mass range of 22–35 kDa and high molecular mass material >150 kDa. The results suggest that the developed S. iniae vaccine has broad ranging protection among isolates exhibiting different protein profiles.     

Immunity to Ostertagia ostertagi

Control of ostertagiasis is a major economic problem in the temperate areas of the world. An immunological control scheme for cattle is an important aspect of integrated control and its achievement is dependent on our understanding of how immunity is acquired. Also, host mechanisms regulated by Ostertagia need to be understood in order to address immunological questions. Little is known about acquired immunity to Ostertagia infection in cattle. The degree of immunity is incomplete and its development slow. Evidence is accumulating for impairment of antibody and cellular immune responses by Ostertagia which is responsible for the survival of the parasite in the young host. Other experimental work suggests that local factors, such as eosinophil accumulation, mucosal mast cell kinetics and other cellular and humoral immune responses, may play a role in pathogenesis and immunity. At the present time these areas are also totally unexplored in the study of Ostertagia infection.     

Development of an indirect enzyme-linked immunoabsorbent assay using a monoclonal antibody to identify Ictalurus sp. fillets

The deceptive marketing of imported basa, Pangasius bocourti (Sauvage), fillets as catfish has resulted in serious economic losses to the channel catfish, Ictalurus punctatus (Rafinesque), industry in the US. The similar appearance of channel catfish and basa fillets created a need for a rapid method to differentiate uncooked, cooked and/or marinated channel catfish fillets from basa fillets and other fish products. A monoclonal antibody (MAb) specific for a 36.8 kDa channel catfish fillet protein was produced and characterized by an indirect enzyme‐linked immunoabsorbent assay (ELISA) and Western blotting. This MAb was used to develop an indirect ELISA specific for a fillet protein unique to fish of the genus Ictalurus. Using this ELISA, 100% of raw and cooked channel catfish fillets were correctly identified and differentiated from other fish in a single‐blind study. These results show that the indirect ELISA using MAbs specific for unique Ictalurus sp. fillet proteins is a rapid and sensitive method for the identification of raw and cooked catfish fillets.