Effects of ascorbic acid and iron nanoparticles supplements on hyperthermia-induced stress in African catfish, Clarias gariepinus (Burchell, 1822)

Background Thermal stressors in tropical aquaculture are unavoidable and cause many harmful effects. This study assessed the effects of ascorbic acid (AA) and iron nanoparticles supplementation in the diet of African catfish, Clarias gariepinus, and exposed to hyperthermia-induced stress. C. gariepinus juveniles weighing 6.89 ± 0.05 g were randomly distributed into plastic tanks of 48 cm by 30 cm by 31 cm dimension at ten fish per tank in a triplicate treatment. Five isonitrogenous and isocaloric diets containing 35% crude protein were formulated with AA and iron nanoparticles supplementation at (10, 8, 6, 4, 0) g/kg of AA and (0, 4, 6, 8, 0) g/kg of iron nanoparticles in treatment 1, 2, 3, 4 and 5, respectively. After 8 weeks of feeding, fish were exposed to hyperthermia-induced stress. Blood was collected from the fish for haematological and biochemical analyses. Results Results showed that there were significant differences (P < 0.05) in the growth performance and nutrient utilization of fish subjected to hyperthermia-induced stress. Treatment three had the highest specific growth rate of 1.89 g per day and the best feed conversion ratio (FCR) of 1.48. Conclusion Mortality was reduced with the supplementation of the fish diets with AA and iron nanoparticles. Based on the result of this study, a supplementation level containing AA and iron nanoparticles supplementation of 6 g/kg and 4 g/kg were sufficient as a stress-reducing agent in the production of C. gariepinus during hyperthermia stress.

Characteristics of hemolysins from pathogenic bacteria in tropical aquaculture: an in-silico study

Some species of known pathogenic bacteria isolates in tropical aquaculture produces hemolysin. Hemolysin can be identified based on its ability to break down red blood cells in vitro. Some hemolysin is a pore-shaped poison that can damage cell membranes and kill host cells. The character of the 13 sequences of hemolysin protein in several pathogenic bacterial isolates in tropical aquaculture was analysed using the NCBI protein bioinformatics database. The phylogenetic tree was generated, and the analysis was conducted using the base character method (Maximum Parsimony) of Mega 6.06 software. The result showed that there are two big family of hemolysin from the known pathogenic bacteria. The closest characteristics of protein sequences were hemolysin of Streptococcus agalacticae and of S. iniae.

Diagenetic Processes in Aquaculture Ponds Showing Metal Accumulation on Shrimp Gills

The gill is the organ by which many toxic metals are taken up by crustaceans. Iron is known to precipitate at its surface, a phenomenon recently observed in some tropical aquaculture ponds. The present study uses a field approach to understand better the environmental conditions and ecological processes involved in this deposit. Because shrimp are exposed to reduced products originating from organic waste accumulated in the sediment, spatial variation in pH, redox potential and concentrations of dissolved metals in pore water were investigated in these ponds. Total organic carbon, acid volatile sulfide and pyrite were also analyzed in the solid phase. Fe2+ in pore waters showed high spatial variability between ponds and within the same pond with concentrations up to 1,193 μmol l–1. Behaviors of Fe2+, Mn2+ and Co2+ in pore water were similar. Four geochemical environments were identified, based on their physico-chemical characteristics. Highest concentrations for Fe2+, Mn2+ and Co2+ in sediment pore water occurred in slightly acidic and suboxic conditions. When the sediment became anoxic, the H2S produced reacted with Fe2+ and/or Co2+ to form acid volatile sulfide and pyrite. When pH increased, the concentration of free H2S rose up to 736 μmol l–1. With neutral and suboxic conditions, dissolved metal concentrations could be controlled by their precipitation as oxides and hydroxides. The production of pyrite suggested the existence of a possible process of sediment acidification between two crop periods through the production of sulfuric acid. This acidification could increase with pond age and be the cause of the accumulation of reduced metal after 30 years of aquaculture activity.

Community Structure of Protease-Producing Bacteria Cultivated From Aquaculture Systems: Potential Impact of a Tropical Environment

Protease-producing bacteria play vital roles in degrading organic matter of aquaculture system, while the knowledge of diversity and bacterial community structure of protease-producing bacteria is limited in this system, especially in the tropical region. Herein, 1,179 cultivable protease-producing bacterial strains that belonged to Actinobacteria, Firmicutes, and Proteobacteria were isolated from tropical aquaculture systems, of which the most abundant genus was Bacillus, followed by Vibrio. The diversity and relative abundance of protease-producing bacteria in sediment were generally higher than those in water. Twenty-one genera from sediment and 16 genera from water were identified, of which Bacillus dominated by Bacillus hwajinpoensis in both and Vibrio dominated by Vibrio owensii in water were the dominant genera. The unique genera in sediment or water accounted for tiny percentage may play important roles in the stability of community structure. Eighty V. owensii isolates were clustered into four clusters (ET-1–ET-4) at 58% of similarity by ERIC-PCR (enterobacterial repetitive intergenic consensus-polymerase chain reaction), which was identified as a novel branch of V. owensii. Additionally, V. owensii strains belonged to ET-3 and ET-4 were detected in most aquaculture ponds without outbreak of epidemics, indicating that these protease-producing bacteria may be used as potential beneficial bacteria for wastewater purification. Environmental variables played important roles in shaping protease-producing bacterial diversity and community structure in aquaculture systems. In sediment, dissolved oxygen (DO), chemical oxygen demand (COD), and salinity as the main factors positively affected the distributions of dominant genus (Vibrio) and unique genera (Planococcus and Psychrobacter), whereas temperature negatively affected that of Bacillus (except B. hwajinpoensis). In water, Alteromonas as unique genus and Photobacterium were negatively affected by NO3−-N and NO2−-N, respectively, whereas pH as the main factor positively affected the distribution of Photobacterium. These findings will lay a foundation for the development of protease-producing bacterial agents for wastewater purification and the construction of an environment-friendly tropical aquaculture model.

The contribution of small-scale, privately owned tropical aquaculture to food security and dietary diversity in Bolivia

New aquaculture systems are emerging in new contexts around the world in part due to aquaculture’s perceived development benefits. However, linkages between aquaculture and food security in these systems are unclear. This study investigated the impact of emerging small-scale, business-oriented fish culture in central Bolivia on the food security and dietary diversity of aquaculture producers (n = 40) and workers (n = 26) in the value chain and compared them to local non-aquaculture farmers (n = 40). Three pathways were investigated: fish consumption, household income, and women’s participation. Food insecurity was widespread and did not vary in a statistically significant way between groups, but a trend toward greater food security amongst aquaculture producers was observed. Dietary diversity was highly homogenous, with the notable exception of high fish consumption amongst producers. Aquaculture was related to higher income, and income has a modest positive effect on food security for aquaculturists and non-aquaculture farmers, but not aquaculture value chain workers. Income did not have an effect on dietary diversity. Women’s involvement in aquaculture was correlated positively to productivity, profitability, and size of operation, while male-only aquaculture was negatively correlated to these. The value chain generated employment, especially for women, but average wages were higher for men. The research provides important insight into aquaculture-food security linkages by showing that the introduction of small-scale business-oriented aquaculture systems can provide nutritious products for regional consumption and can have positive effects on food security but is not sufficient to change local dietary preferences more broadly.

SOME TRENDS IN FRESHWATER TROPICAL AQUACULTURE AND THEIR IMPACT ON STUDIES OF THE CLIMBING PERCH ANABAS TESTUDINEUS (ANABANTIDAE) REPRODUCTIVE BIOLOGY

The dynamics of publication activities devoted to the climbing perch from 1969 to 2018 is analyzed. It is shown that sharp increases in the number of publications at the turn of the millennium coincide with changes in international and national strategies for tropical fish aquaculture, focusing on cultivation of fast-growing native fish species and small farms support. These programs have led to a surge in applied research and publications on the climbing perch, as one of the most promising species. Unfortunately, some of these papers have been published in journals that are unreliable according to the criteria of contemporary science and contain controversial conclusions. Certain consequences of these trends are noted and challenges outlined.

Ecology of Pseudodiaptomus annandalei in tropical aquaculture ponds with emphasis on the limitation of production

ABSTRACT The calanoid copepod Pseudodiaptomus annandalei is used as live feed in aquaculture because of its nutritional value and the ability to cope with environmental fluctuations in outdoor ponds. However, little knowledge exists on its ecology. Here we investigated the ecology of P. annandalei in an aquaculture pond in Vietnam. Temperature, salinity, chlorophyll a and biomass of protozoans and copepods were monitored every other day for 1 month. Experiments on protozoan growth and grazing by P. annandalei were also conducted. Copepod fecal pellet production and temperature-dependent egg hatching rates were likewise quantified. Despite very high phytoplankton biomass, biomass of P. annandalei was surprisingly low. Copepod production was estimated from three independent methods: clearance, weight-specific egg production rate (SEP) and specific fecal pellet production rate. SEP proved to be accurate to predict the in situ population growth in the pond. A simple model for production of P. annandalei based on SEP was developed. Our study extends our knowledge of how environmental conditions in the pond may affect the population dynamics and production of copepods. The results have important implications for pond managements ensuring stable copepod production and harvest.