Fatty acid composition of red drum maintained by fishmeal, fish oil substitutes in diets

Recent research by the authors evaluated strategies to reduce fishmeal and fish oil in diets for red drum by substituting terrestrial proteins and lipids while maintaining beneficial fatty acids with DHA supplements derived from marine algae. Results suggested fatty acid-enriched finishing diets can be used with growout diets containing little or no fishmeal and fish oil to achieve the desired DHA content in the final fish fillets

Induction of Antiviral Immunity by Double-Stranded RNA in a Marine Invertebrate

Vertebrates mount a strong innate immune response against viruses, largely by activating the interferon system. Double-stranded RNA (dsRNA), a common intermediate formed during the life cycle of many viruses, is a potent trigger of this response. In contrast, no general inducible antiviral defense mechanism has been reported in any invertebrate. Here we show that dsRNA induces antiviral protection in the marine crustacean Litopenaeus vannamei. When treated with dsRNA, shrimp showed increased resistance to infection by two unrelated viruses, white spot syndrome virus and Taura syndrome virus. Induction of this antiviral state is independent of the sequence of the dsRNA used and therefore distinct from the sequence-specific dsRNA-mediated genetic interference phenomenon. This demonstrates for the first time that an invertebrate immune system, like its vertebrate counterparts, can recognize dsRNA as a virus-associated molecular pattern, resulting in the activation of an innate antiviral response

Practical diets for Litopenaeus Vannamei (Boone, 1931): working towards organic and/or all plant production diets.

As shrimp prices become more competitive and the profit margins declining, producers are looking to high value markets for their products. Shrimp produced using organic or environmentally friendly production conditions have the potential to bring in higher prices through market differentiation. However, if one is to develop production schemes for such markets, one must also produce an organic feed or one that has minimal levels of marine proteins and oils. In previous research we developed a practical diet formulation without fish meal but containing marine fish oil. Since supplies of fish oil are also limited, this work concentrated on replacement of the marine oil source as well as the testing of an experimental organic diet. In the first experiment, fish oil in two of the diets was substituted by oil originating from commercially produced algae containing approximately 50% oil. These diets as well as a commercial feed were offered to juvenile Litopenaeus vannamei (Boone, 1931) over a 15 week growth trial. At the conclusion of the growth trial, survival, final weight, and feed conversion ratio (FCR) were not significantly different among treatments. In the second experiment, the diet previously tested using plant and algae oils was tested against a diet using only plant oils. To examine the potential of an organic diet, a practical diet using primarily organic ingredients was also tested. The three diets were tested in conjunction with a commercial control diet over a 12-week growth period. At the conclusion of this trial, shrimp reared on the organic diet and the diet without algae oil supplements were significantly smaller than those offered the commercial control. This result is presumably due to a lack of HUFA in the diets without algae oils high in DHA and AA. To further test the potential of a feed without fish meal, a commercial version of one of the test diets was produced at a feed mill and tested under pond production conditions. As this was only a demonstration, statistical differences cannot be determined but the feed did appear to produce acceptable results under commercial pond production conditions. Based on the results of these studies, it would appear that both fish meal and marine oil sources can be removed from shrimp feeds if suitable alternative sources of protein and lipids are provided to meet essential amino acid and fatty acid requirements of the shrimp

Double-Stranded RNA Induces Sequence-Specific Antiviral Silencing in Addition to Nonspecific Immunity in a Marine Shrimp: Convergence of RNA Interference and Innate Immunity in the Invertebrate Antiviral Response?

Double-stranded RNA (dsRNA) is a common by-product of viral infections and a potent inducer of innate antiviral immune responses in vertebrates. In the marine shrimp Litopenaeus vannamei, innate antiviral immunity is also induced by dsRNA in a sequence-independent manner. In this study, the hypothesis that dsRNA can evoke not only innate antiviral immunity but also a sequence-specific antiviral response in shrimp was tested. It was found that viral sequence-specific dsRNA affords potent antiviral immunity in vivo, implying the involvement of RNA interference (RNAi)-like mechanisms in the antiviral response of the shrimp. Consistent with the activation of RNAi by virus-specific dsRNA, endogenous shrimp genes could be silenced in a systemic fashion by the administration of cognate long dsRNA. While innate antiviral immunity, sequence-dependent antiviral protection, and gene silencing could all be induced by injection of long dsRNA molecules, injection of short interfering RNAs failed to induce similar responses, suggesting a size requirement for extracellular dsRNA to engage antiviral mechanisms and gene silencing. We propose a model of antiviral immunity in shrimp by which viral dsRNA engages not only innate immune pathways but also an RNAi-like mechanism to induce potent antiviral responses in vivo

Identification of Bacillus strains for biological control of catfish pathogens.

Bacillus strains isolated from soil or channel catfish intestine were screened for their antagonism against Edwardsiella ictaluri and Aeromonas hydrophila, the causative agents of enteric septicemia of catfish (ESC) and motile aeromonad septicaemia (MAS), respectively. Twenty one strains were selected and their antagonistic activity against other aquatic pathogens was also tested. Each of the top 21 strains expressed antagonistic activity against multiple aquatic bacterial pathogens including Edwardsiella tarda, Streptococcus iniae, Yersinia ruckeri, Flavobacterium columnare, and/or the oomycete Saprolegnia ferax. Survival of the 21 Bacillus strains in the intestine of catfish was determined as Bacillus CFU/g of intestinal tissue of catfish after feeding Bacillus spore-supplemented feed for seven days followed by normal feed for three days. Five Bacillus strains that showed good antimicrobial activity and intestinal survival were incorporated into feed in spore form at a dose of 8×10(7) CFU/g and fed to channel catfish for 14 days before they were challenged by E. ictaluri in replicate. Two Bacillus subtilis strains conferred significant benefit in reducing catfish mortality (P<0.05). A similar challenge experiment conducted in Vietnam with four of the five Bacillus strains also showed protective effects against E. ictaluri in striped catfish. Safety of the four strains exhibiting the strongest biological control in vivo was also investigated in terms of whether the strains contain plasmids or express resistance to clinically important antibiotics. The Bacillus strains identified from this study have good potential to mediate disease control as probiotic feed additives for catfish aquaculture