Tilapia culture: The basics

This new aquaculture extension manual revisits the basics of tilapia culture with updated information on the grow-out technology in cages and ponds. Updated cost and returns analyses were also included to guide farmers regarding the profitability of farming tilapia. A fresh chapter on tilapia health management is also included to promote the prevention of tilapia diseases

Efficacy of the inactivated nervous necrosis virus vaccine against viral nervous necrosis in pond-reared orange-spotted grouper Epinephelus coioides

The field efficacy of the formalin-inactivated nervous necrosis virus (NNV) against viral nervous necrosis (VNN) in orange-spotted grouper (Epinephelus coioides) reared in floating net cages in earthen pond was investigated. Seroneutralization assay conducted on the sera of vaccinated fish exhibited the occurrence of neutralizing antibody titers from Day 30 (mean titer 1:1792±701) to Day 150 (1:704±351) with the highest titer observed at Day 60 (1:6656±3435) post-vaccination. Because mortality attributed to VNN was not encountered during the pond experiment, intramuscular challenges of vaccinated and unvaccinated (L-15 injected) fish with NNV (106.5 TCID50/fish) were conducted in indoor tanks at Day 30 (Mean body weight [MBW]: vaccinated [21±3.4 g]; unvaccinated [20.6±1 g) and Day 120 (MBW: vaccinated [178±27 g]; unvaccinated [176±19 g) postvaccination, respectively, to demonstrate the in vivo efficacy of the inactivated vaccine. Nil and 25 % mortality rate were obtained in vaccinated and control fish, respectively, challenged with NNV at Day 30 post-vaccination. On the contrary, nil mortality were obtained in both groups challenged with NNV at Day 120 post-vaccination. Although nil mortality was obtained in NNV-challenged unvaccinated fish, 30 % of the fish manifested dark coloration of the skin and abnormal swimming behavior that commenced and disappeared at Day 3 and Day 7 post-NNV challenge, respectively, suggesting an age/ weight-dependent resistance to the disease. Our current data illustrate that single vaccination with inactivated vaccine could mount the production of protective antibodies and concomitant conferment of protection against VNN in groupers especially during the early phase of grow-out culture in earthen ponds where they are highly susceptible to the disease.This study was funded by Government of Japan Trust Fund VI through the Regional Fish Disease Project (study code: FH01- F2015-T) and in part by SEAFDEC/ AQD. We express our heartfelt gratitude to Dr. Takuro Shibuno and Dr. Chihaya Nakayasu, former GOJ-TF managers, Dr. Koh Ichiro Mori, current GOJ-TF manager, and the Marine Fish Hatchery staff especially Mr. A. Gamuza

The impact of co-infections on fish: a review

International audienceAbstractCo-infections are very common in nature and occur when hosts are infected by two or more different pathogens either by simultaneous or secondary infections so that two or more infectious agents are active together in the same host. Co-infections have a fundamental effect and can alter the course and the severity of different fish diseases. However, co-infection effect has still received limited scrutiny in aquatic animals like fish and available data on this subject is still scarce. The susceptibility of fish to different pathogens could be changed during mixed infections causing the appearance of sudden fish outbreaks. In this review, we focus on the synergistic and antagonistic interactions occurring during co-infections by homologous or heterologous pathogens. We present a concise summary about the present knowledge regarding co-infections in fish. More research is needed to better understand the immune response of fish during mixed infections as these could have an important impact on the development of new strategies for disease control programs and vaccination in fish

Identification of Pseudomonas sp. strain S3 based on small subunit ribosomal RNA gene sequences

Pseudomonas sp. strain S3 was isolated from Paddy (rice) field agricultural area. This organism, which can utilize a halogenated compound of D,L-2-Chloropropionic acid as sole carbon and energy source, catalyses the hydrolytic dehalogenation of both D- and L- isomers of 2-Chloropropionic acid. Identification of Pseudomonas sp. S3 is still ambiguous due to the lack of basic studies, especially their molecular genetic information. In this study, the amplified 16S rRNA gene sequence of Pseudomonas sp. S3 (Accession No. FJ968758) was compared to other nine selected gene sequences from the same group of Pseudomonas sp. and/or dehalogenase producing bacteria using in silico method. Their phylogenetic relationships were then determined. The results were analysed using MEGA4 software to ascertain its evolutionary distance by reconstructing a phylogenetic tree of these organisms. The evolutionary history and bootstrap consensus tree were inferred using the Neighbour-Joining method from 500 replicates. The tree is drawn to scale, with branch lengths (next to the branches) in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the p-distance method and were in the units of the number of base substitutions per site. Based on this analysis, Pseudomonas sp. S3 16S rRNA gene was closely related to the Pseudomonas chlororaphis with genetic distance 0.170 base substitutions per site. S3 gene was also compared among known dehalogenase producing bacteria 16S rRNA genes. Results suggested that S3 was closely related to the Pseudomonas sp. R1 with a genetic distance 0.040 base substitutions per site. From present study, evolutionary relationships of 16S rRNA gene of Pseudomonas sp. S3 were elegantly illustrated by phylograms, comparable to a pedigree showing which microorganisms are most closely related

Aeromonas load and species composition in tilapia (Oreochromis niloticus) cultured in earthen ponds in the Philippines

Aeromonas load and species composition in the rearing water, sediment, gills and intestines of healthy tilapia Oreochromis niloticus collected every 2 weeks from Days 30 to 120 after stocking in six earthen ponds in the Philippines were determined. Presumptive Aeromonas counts (PACs) in the water and sediment ranged from 101–103 c.f.u./ml and 101–103 c.f.u./g while in the gills and intestines, PACs ranged from 104–107 c.f.u./g and 102–105 c.f.u./g, respectively. Presumptive Aeromonas counts in the water, sediment, and gills of tilapia varied among days of culture while in the intestines of tilapia, PACs markedly dropped by approximately 2 logs at Day 75 and either remained in the same level or decreased by another 1 log at Day 120 of grow‐out culture. Aeromonas hydrophila predominantly constituted 94% of all presumptive Aeromonas spp. examined (n = 343), followed by A. sobria (4%) and A. salmonicida (2%). Taken together, current data provide some putative threshold levels of tilapia reared in earthen ponds to Aeromonas spp. The dominance of A. hydrophila together with negligible population of A. salmonicida and A. sobria indicate that Aeromonas are common commensal bacteria in tilapia and their environment which under conditions of stress could instigate disease epizootics.This study was funded by the Department of Science and Technology-National Research Council of the Philippines (DOST-NRCP; NRCP project no. E-225) and partly by SEAFDEC AQD (study code: FH02-F2013-T). We would like to thank Dr. Evelyn Grace de Jesus-Ayson for the critical review of the manuscript, and Mr. Eric Ledesma and the laboratory staff of NPPMCI for the invaluable assistance during our sampling

Environmental and other non-infectious diseases

The chapter presents some of the environmental non-infectious diseases of aquatic animals. Non-infectious diseases are caused by adverse environmental conditions, nutritional disorders, or genetic defects. While they can result a sudden mass mortality or death, they are not contagious. Environmental diseases are the most important in aquaculture. This includes low dissolved oxygen, high ammonia, high nitrite, or natural or man-made toxins in the aquatic environment

Quantitative and qualitative analyses of the bacterial microbiota of tilapia (Oreochromis niloticus) cultured in earthen ponds in the Philippines

The quantity and composition of the bacterial microbiota in the rearing water, sediment, gills and intestines of tilapia Oreochromis niloticus collected every 2 weeks from Day 30 to Day 120 after stocking for grow-out culture in 6 earthen brackish water ponds in the Philippines were examined. The total heterotrophic aerobic bacterial counts obtained in the water, sediment, gills and intestines of tilapia ranged from 103 to 104 c.f.u. ml−1, 103–105, 105–107 and 104–107 c.f.u. g−1, respectively. In terms of composition, a total of 20 bacterial genera and 31 species were identified with the preponderance of gram-negative bacteria constituting 84% of all bacterial isolates examined. Aeromonas hydrophila, Bacillus spp., Plesiomonas shigelloides, Shewanella putrefaciens, Pseudomonas fluorescens, Staphylococcus spp. and Vibrio cholerae were the dominant bacteria identified in the gills and intestine of tilapia. These bacteria also dominated in the pond sediment and rearing water, except for the nil isolation of S. putrefaciens and V. cholerae in the water samples examined, indicating that resident bacteria in the pond water and sediment congruently typify the composition of bacterial microbiota in the gills and intestine of tilapia which under stressful conditions may propel the ascendance of disease epizootics

アクアビルナウイルスによるVNN抵抗性の誘導

非病原性アクアビルナウイルス(ABV)を予め接種され、その 7 日後にベータノダウイルス(NNV)で攻撃されたマハタは NNV 感染に対して強い抵抗性を示した。他方、ヒラメではNNVに対する感受性が低いため死亡率からABVの効果をみることはできなかったが、脳および腎臓におけるNNVの消長をみると、両魚種とも ABV 処理魚において明らかにウイルス感染力価の低下が認められた。この防御は、ABVにより誘導されるインターフェロン関連タンパク質に因ると考えられた。Experimental dual-infections with a non-lethal aquabirnavirus (ABV) and a lethal betanodavirus (redspotted grouper nervous necrosis virus: RGNNV) were carried out in Japanese flounder Paralichthys olivaceus and sevenband grouper Epinephelus septemfasciatus. In the dual-infection group, ABV was intramuscularly (IM) injected into fish seven days before the IM-injection with RGNNV. In the experiments with flounder, a high expression of an Mx gene, a molecular marker for type I interferon(s) (IFM) production, occurred in the head kidneys and brains at Day 7 post-ABV injection. Although-no mortality was found not only in the dual-infected group but also in the single infection group with RGNNV (control group), the infective titers of RGNNV in the tissues of the dual-infected group were significantly lower at any sampling times than those in the control group. In the experiments with grouper, the preceding ABV infection resulted in complete protection against RGNNV infection. The infective titers of RGNNV in the tissues were also lower in the dual-infected group than in the control group throughout the experiments, and finally the virus disappeared from the head kidneys and brains of the dual-infected group at Day 14 and Day 56 postinjections, respectively. These results suggest that an ABV-induced IFN(s) effectively suppresses the progression of secondary betanodavirus infection

Studies on the efficacy of Sarafin® (sarafloxacin hydrochloride) on vibrios associated with vibriosis in black tiger shrimp (Penaeus monodon)

In vitro activity of Sarafin® (sarafloxacin hydrochloride) was determined against 7 luminous Vibrio harveyi isolates and 3 non-luminous Vibrio species (V. parahaemolyticus, V. alginolyticus and Vibrio species) isolated from diseased shrimp (Penaeus monodon) and rearing water, a strain of V. anguillarum from diseased marine fish, 1 strain each of V. alginolyticus, V. vulnificus, and V. mimicus from diseased grouper (Epinephelus coioides), and V. alginolyticus from diseased seabass (Lates calcarifer). Bacterial susceptibility was expressed as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The MIC and MBC values obtained for all V. harveyi isolates ranged from 50 µg/ml Sarafin®. These results indicate that Sarafin® is a potential candidate as a chemotherapeutic agent against luminous vibriosis in P. monodon