Blood and liver biopsy for the non‐destructive screening of tilapia lake virus

Detection of tilapia lake virus (TiLV) in tilapines is mainly from visceral organs of killed fish. However, lethal sampling might not be viable to broodstock and economically important ornamental cichlids. To contribute towards screening of the virus in asymptomatic infected fish, a subclinically infected population of Nile tilapia adults obtained from a local farm was preliminarily tested to compare different non‐lethal sampling methods, for example liver biopsy, gill biopsy, fin clip, mucus, faeces and blood for detection of TiLV. Only liver and blood samples gave positive results by PCR. Since blood sampling is relatively simpler, it was further used for five naturally co‐cultured juvenile fish species from above‐mentioned farm including 40 red tilapia broodstock and 20 Nile tilapia adults from two other different farms. The results showed that from the tested fish, 4 of 5 Nile tilapia, 2 of 5 hybrid red tilapia and 3 of 5 giant gourami blood samples tested positive, while 38 of 40 blood samples of red tilapia tested positive for TiLV in second‐step PCR. Sequencing representative PCR amplicons of positive samples confirmed sequence identity to TiLV. In conclusion, both blood and liver biopsy are practical non‐destructive sampling platforms for TiLV screening in cichlids with blood being more convenient, especially for tilapia broodstock.     

A multi-epitope chimeric protein elicited a strong antibody response and partial protection against Edwardsiella ictaluri in Nile tilapia

Edwardsiella ictaluri infects several fish species and protection of the all the susceptible fish hosts from the pathogen using a monovalent vaccine is impossible because the species is composed of host-based genotypes that are genetic, serological and antigenic heterogenous. Here, immunoinformatic approach was employed to design a cross-immunogenic chimeric EiCh protein containing multi-epitopes. The chimeric EiCh protein is composed of 11 B-cell epitopes and 7 major histocompatibility complex class II epitopes identified from E. ictaluri immunogenic proteins previously reported. The 49.32 kDa recombinant EiCh protein was expressed in vitro in Escherichia coli BL-21 (DE3) after which inclusion bodies were successfully solubilized and refolded. Ab initio protein modelling revealed secondary and tertiary structures. Secondary structure was confirmed by circular dichroism spectroscopy. Antigenicity of the chimeric EiCh protein was exhibited by strong reactivity with serum from striped catfish and Nile tilapia experimentally infected with E. ictaluri. Furthermore, immunogenicity of the chimeric EiCh protein was investigated in vivo in Nile tilapia juveniles and it was found that the protein could strongly induce production of specific antibodies conferring agglutination activity and partially protected Nile tilapia juveniles with a relative survival percentage (RPS) of 42%. This study explored immunoinformatics as reverse vaccinology approach in vaccine design for aquaculture to manage E. ictaluri infections.     

Bacteriostatic effect of flavonoids isolated from leaves of Psidium guajava on fish pathogens

The antimicrobial activity against fish bacterial pathogens of flavonoids (morin, morin-3-O-lyxoside, morin-3-O-arabinoside, quercetin, and quercetin-3-O-arabinoside) isolated from the leaves of Psidium guajava was evaluated. The flavonoids were shown to have bacteriostatic effect on all of the tested bacteria.     

Combinations of trees and crops in the taungya method as applied in Thailand

In Thailand the taungya reforestation method has been practiced primarily in order to rehabilitate wasteland, particularly under the Forest Village Programme. While various combinations of trees and crops are found in the taungya method on a minor scale, the major combinations are teak with upland rice in the north, fast-growing trees with cassava in the northeast, fast-growing trees with maize in the west, and para-rubber or fast-growing trees with fruit trees in the south. These combinations relate to the differences in climatic conditions, mainly the duration of the rainy season.     

Effect of <Emphasis Type="Italic">Cratoxylum formosum</Emphasis> on innate immune response and disease resistance against <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> in tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

The effect of aqueous extract of Cratoxylum formosum on innate immune response and disease resistance in tilapia Oreochromis niloticus was investigated. The fish were fed diets containing 0% (control), 0.5% (diet 1), 1% (diet 2), and 1.5% (diet 3) of C. formosum aqueous extract for 30 days. At the end of the experimental period, parameters of innate immune response including phagocytosis of blood leukocytes, lysozyme activity in plasma, and respiratory bust activity were examined. Feeding the fish with diet 2 and diet 3 for 20 days enhanced phagocytic activity and for 30 days stimulated lysozyme and respiratory burst activities. Diet 1 increased the phagocytic activity at 30 days, but did not affect the other measured parameters. All parameters were not significantly changed (P > 0.05) in the control group throughout the experiment. Following 30 days of feeding, fish were infected with S. agalactiae. The cumulative mortalities of bacterial-infected tilapia that were fed diet 1, diet 2, and diet 3 were 56, 12, and 10%, respectively, compared with 85% in the control group. These results indicate that the aqueous extract of C. formosum may elevate the innate immune response and enhance disease resistance in tilapia.     

Aeromonas jandaei and Aeromonas veronii caused disease and mortality in Nile tilapia,Oreochromis niloticus (L.)

Diseases caused by motile aeromonads in freshwater fish have been generally assumed to be linked with mainly Aeromonas hydrophila while other species were probably overlooked. Here, we identified two isolates of non‐A. hydrophila recovered from Nile tilapia exhibiting disease and mortality after exposed to transport‐induced stress and subsequently confirmed their virulence in artificial infection. The bacterial isolates were identified as Aeromonas jandaei and Aeromonas veronii based on phenotypic features and homology of 16S rDNA. Experimental infection revealed that the high dose of A. jandaei (3.7 × 10⁶ CFU fish^?1) and A. veronii (8.9 × 10⁶ CFU fish^?1) killed 100% of experimental fish within 24 h, while a 10‐fold reduction dose killed 70% and 50% of fish, respectively. When the challenge dose was reduced 100‐fold, mortality of the fish exposed to A. jandaei and A. veronii decreased to 20% and 10%, respectively. The survivors from the latter dose administration were rechallenged with respective bacterial species. Lower mortality of rechallenged fish (0%–12.5%) compared to the control groups receiving a primary infection (37.5%) suggested that the survivors after primary infection were able to resist secondary infection. Fish exposed to either A. jandaei or A. veronii exhibited similar clinical signs and histological manifestation.     

Potential of cinnamon (<Emphasis Type="Italic">Cinnamomum verum</Emphasis>) oil to control <Emphasis Type="Italic">Streptococcus iniae</Emphasis> infection in tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

In this study, four essential oils—cinnamon oil, leech lime oil, lemongrass oil, and turmeric oil—were examined for their antimicrobial activities against Streptococcus iniae, a bacterium that is pathogenic in fish, in which it causes streptococcosis. Cinnamon oil was the most potent antimicrobial agent among these oils, with a minimal inhibitory concentration (MIC) of 40 μg/ml. By using gas chromatography–mass spectrometry (GC–MS), it was found that the major components of cinnamon oil were cinnamaldehyde (90.24), limonene (2.42%), cinnamyl acetate (2.03%), linalool (1.16%), and α-terpineol (0.87%). Of these compounds, only cinnamaldehyde exhibited antimicrobial activity against S. iniae, with an MIC of 20 μg/ml. In an in vivo trial, no mortality was apparent in fish fed on fish diets supplemented with 0.4% (w/w) of cinnamon oil and with 0.1% (w/w) of oxytetracycline 5 days prior to infection with S. iniae. These results indicate that cinnamon oil had a protective effect on experimental S. iniae infection in tilapia, and thus has the potential to replace the antibiotics used to control this disease.     

Combinations of trees and crops in the taungya method as applied in Thailand

In Thailand the taungya reforestation method has been practiced primarily in order to rehabilitate wasteland, particularly under the Forest Village Programme. While various combinations of trees and crops are found in the taungya method on a minor scale, the major combinations are teak with upland rice in the north, fast-growing trees with cassava in the northeast, fast-growing trees with maize in the west, and para-rubber or fast-growing trees with fruit trees in the south. These combinations relate to the differences in climatic conditions, mainly the duration of the rainy season.     

Potential of Chinese chive oil as a natural antimicrobial for controlling <Emphasis Type="Italic">Flavobacterium columnare</Emphasis> infection in Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

Chinese chive Allium tuberosum oil was studied for its diallyl sulfide content and its antimicrobial activity against Flavobacterium columnare in fish both in vitro and. The oil was found to have a very low concentration of diallyl monosulfide relative to the other diallyl sulfides (diallyl disulfide, diallyl trisulfide, and diallyl tetrasulfide) identified. In the in vitro study, the Chinese chive oil had a bacteriocidal effect on all tested strains of F. columnare, with varied minimal inhibitory concentrations. The median lethal dose (LD₅₀) of FC4 for Nile tilapia Oreochromis niloticus was determined to be 3.72 × 10³ CFU/fish. In the in vivo trial, no mortality was observed in fish fed fish diets supplemented with 800 mg/kg Chinese chive oil and 100 mg/kg of oxytetracycline hydrochloride 5 days prior to infection with F. columnare strain 4 at a LD₅₀. These results indicate that Chinese chive oil has the potential to replace antibiotics for controlling fish disease caused by F. columnare.     

Recent irrigation practices in the Upper East Bank of the Chao Phraya Delta

This study aims to investigate recent practices on water allocation and cultivation in the Upper East Bank of the Chao Phraya Delta in Thailand, by using data collected by RID local offices, questionnaires, and analyses of satellite images. As a result, we have identified the advantage that upstream areas of irrigation canals have enjoyed, namely the preferential water allocation over the downstream areas. This advantage was strongly associated with the intensive cropping patterns of rice: the upstream areas were estimated to conduct almost continuous rice cultivation throughout a year. In addition, the intensive rice cultivation would partly be supported by water from private shallow wells, which were mostly concentrated in the upstream areas of main canals. Those shallow wells would be used at the beginning of the dry season and in drought years, when farmers could not expect water supply from irrigation canals. The result indicated that the conjunctive use of surface and ground water would be practiced in this region.