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

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

Vibrio harveyi-like bacteria associated with fin rot in farmed milkfish Chanos chanos (Forsskal) fingerlings in the Philippines

Milkfish (Chanos chanos) is a commercially important species widely cultured and consumed in the Philippines. It is a hardy fish but due to culture intensification, occurrence of bacterial disease is inevitable. The causative agent of fin rot disease in milkfish fingerlings (total length [TL] = 2.8–4.5 cm) reared in intensive nursery earthen ponds in the Philippines was investigated in the current study. Following biochemical characterization tests and 16S rRNA sequencing, seven isolates recovered from affected fish were identified as Vibrio harveyi-like bacteria. Immersion challenge of milkfish (TL = 5.64 ± 0.76 cm) using a representative strain (CCL-01) at inoculum dose of 108 CFU/mL resulted in fin rot as early as 1-day post-infection (dpi) and concomitant mortalities of 57% ± 0.58 at 7 dpi. Moreover, when milkfish (TL = 6.18 ± 0.66 cm) stocked at 5, 10, and 20 fish/5 L were exposed to the computed 168-h lethal dose (LD50) at 6.63 × 104 CFU/mL, significant mean mortality of 45% ± 1.0 coupled with typical signs of fin rot were particularly obtained in fish stocked at 20 fish/5 L (biomass = 4 g/L) while low mortality of 0% and 7% ± 0.58 were recorded in fish stocked at 5 fish/5 L and 10 fish/5 L, respectively, at 7 dpi. Vibrio harveyi-like bacteria was reisolated in lesions and kidney of all challenged fish while none in any of the control fish. The current data clearly indicate that the isolated V. harveyi-like bacteria is an opportunistic pathogen capable of instigating disease epizootics in milkfish fingerlings stocked at higher densities.This study was funded by the Department of Science and Technology through the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (PCAARRD) under the UPV-DOST Milkfish Program A. Also, Oversea Feeds Corporation, SEAFDEC Aquaculture Department and Dr. Carlo Lazado are greatly acknowledged for the milkfish samples, use of the research facilities and valuable inputs in editing an earlier draft of the paper, respectively

Immune responses of Asian sea bass, Lates calcarifer Bloch, against an inactivated betanodavirus vaccine

Asian sea bass, Lates calcarifer (Bloch), exhibited strong immune responses against a single injection of the formalin-inactivated red-spotted grouper nervous necrosis virus (RGNNV), a betanodavirus originally isolated in Japan. Fish produced neutralizing antibodies at high titre levels from days 10 (mean titre 1:480) to 116 (1:1280), with the highest titre at day 60 post-vaccination (1:4480). When fish were challenged with the homologous RGNNV at day 54 post-vaccination, there were no mortalities in both the vaccinated and unvaccinated control fish. However, a rapid clearance of the virus was observed in the brains and kidneys of vaccinated fish, followed by a significant increase in neutralizing-antibody titres. Furthermore, the vaccine-induced antibodies potently neutralized Philippine betanodavirus isolates (RGNNV) in a cross-neutralization assay. The present results indicate the potential of the formalin-inactivated RGNNV vaccine against viral nervous necrosis (VNN) of Asian seabass.We would like to thank Dr. Gilda Lio-Po for giving valuable suggestions on this study. We also gratefully acknowledge Dr. Evelyn Grace de Jesus-Ayson and some staff of Finfish Hatchery and Biolab for their kind assistance during the experiment. This study was funded in part by the Government of Japan Trust Fund through the Regional Fish Disease Project (study code: 8001-T-FT-FH0507) and by a Grant-in-Aid for Scientific Research (No.18076) from the Ministry of Agriculture, Forestry and Fisheries of Japan

Bacterial microbiota of hatchery-reared freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and their pathogenicity

Quantitative and qualitative analyses of bacterial microbiota associated with hatchery of Macrobrachium rosenbergii (de Man, 1879) were conducted over three larval cycles, along with important water quality parameters. Physicochemical parameters (temperature, DO, salinity, pH, and total ammonia) of culture water were within the optimum level required for the hatchery phase of M. rosenbergii. Significant differences in aerobic plate count (APC) among larval stages were observed. Ten genera and 17 species were identified with the predominance of Gram-negative bacteria constituting 63 % of all isolates (n = 706). A total of 17 dominant bacterial isolates randomly selected from freshwater prawn larvae were screened for in vitro hemolysin activity using blood agar plate (BAP) medium with 5% sheep blood. Pathogenicity of the isolated bacterial strains was assessed through in vivo infection bioassay. Out of the 17 isolates tested, six isolates showed α – β zone of hemolysis on the BAP, i.e., Aeromonas caviae, Bacillus cereus, Plesiomonas shigelloides, Staphylococcus warneri, Vibrio cholerae non-01, and Vibrio furnissii, were used in the infection bioassay. The current data indicate that the six bacterial isolates tested, particularly B. cereus and V. cholerae non-01, are opportunistic pathogens capable of inducing disease epizootics, particularly in freshwater prawn hatcheries with suboptimal rearing water conditions. Thus, control measures to reduce the influx of pathogenic microbes in the system by maintaining good water quality and good farm management practices through disinfection of culture facilities, rearing water, and Artemia cysts, the practice of good hygiene of personnel, regular water exchange, and feed regulation, among others, and cautionary use of antibiotics, can be adopted

Bacterial microbiota of hatchery-reared freshwater prawn Macrobrachium rosenbergii (de Man, 1879)

Quantitative and qualitative analyses of bacterial microbiota associated with hatchery of freshwater prawn Macrobrachium rosenbergii (de Man, 1879) were conducted over three larval cycles, along with important water quality parameters. Physicochemical parameters (temperature, DO, salinity, pH and total ammonia) of culture water were within the optimum level required for the hatchery phase of M. rosenbergii. Aerobic plate count (APC) (log10 CFU.mL-1) ranged from 4.2 ± 0.18–8.7 ± 0.01 in rearing water and (log10 CFU.g-1) 3.3 ± 0.12–9.1 ± 1.1 in eggs and larvae. Significant differences in APCs among larval stages were observed. Ten genera and 17 species were identified with the predominance of Gram-negative bacteria constituting 63 % of all isolates (n = 706). Acinetobacter baumannii, Acinetobacter lwoffii, Chryseobacterium indologenes, Enterobacter aerogenes, Enterobacter cloacae, Vibrio furnissii, Vibrio cholerae non-01, Plesiomonas shigelloides, Pseudomonas aeruginosa, Pseudomonas pseudoalcaligenes, Bacillus cereus, Staphylococcus haemolyticus, Staphylococcus warneri and Staphylococcus xylosus were predominantly present in culture water. These bacteria likewise dominated in eggs and larvae except for the absence of Ps. aeruginosa, Ps. pseudoalcaligenes, V. cholerae non-01, Staphylococcus epidermidis and Staph. xylosus in eggs, clearly indicating that resident bacteria in water affect the composition of bacteria in eggs and larvae. Some of these are opportunistic pathogens. Thus, control measures to reduce influx of pathogenic microbes in the system by maintaining good water quality and good farm management practices through disinfection of culture facilities, rearing water, Artemia cysts, the practice of good hygiene of personnel, regular water exchange and feed regulation among others and cautionary use of antibiotics can be adopted