Effect of Iron,Nickel and Cobalt on Bacterial Activity and Dynamics During Anaerobic Oxidation of Organic Matter

The present study reports on the effect of Fe²⁺, Ni²⁺ and CO²⁺ on anaerobic bacterial activity and dynamics during anaerobic mineralization of organic matter. Fe²⁺ stimulated biogas yield and methane content at 37 °C, but inhibited same marginally at low temperatures (10 and 20 °C). Ni²⁺ and CO²⁺ inhibited methane production; the toxicity increased with decreasing temperature. Fe²⁺ stimulated sulfate reducing bacterial (SRB) and methane producing bacterial (MPB) counts while Ni²⁺ and CO²⁺ inhibited the same. All the metals had no effect on obligate proton reducing bacterial (OPRB) counts. Fe²⁺ stimulated, Ni²⁺ severely and CO²⁺ appreciably inhibited H₂ uptake and acetate/propionate utilization irrespective of presence/absence of sulfate. Thus, Ni²⁺ and CO²⁺ inhibited the overall anaerobic degradative process by inhibiting SRB and MPB activity.     

Allelic segregation of sex‐linked microsatellite markers in Nile tilapia (Oreochromis niloticus) and validation of inheritance in YY population

Stocking of all‐male fingerling produced by direct administration of male hormone 17‐α‐methyltestosterone is the most preferred method for present‐day aquaculture of the Nile tilapia Oreochromis niloticus. However, due to the growing concern of negative impact of steroid hormone in food fish, production of ‘genetically male’ tilapia, which depends on the concrete and thorough understanding of sex determination, has long been a scientific curiosity. The objective of the present study was to identify reliable sex‐linked markers and to evaluate the applicability of those markers in terms of monosex production approach. ‘XY’ neofemales were produced by using synthetic oestrogen and identified through selective breeding and progeny testing. Three females with progeny not deviating from 3:1 sex ratio (male:female) were designated as ‘XY’ neofemales and were used subsequently to produce putative YY progeny. Among the fifteen microsatellite markers tested, marker ARO172 was most informative in differentiating male and female genotypes. Twenty‐seven F₂ fish from three families were identified as putative YY males based on marker genotyping, and four of them were crossed to produce F₃ to validate marker association by progeny testing. The YY males produced 86%–100% male progeny indicating ARO172 a unique sex‐linked marker applicable in marker‐assisted selection.     

Dietary supplementation of garlic (Allium sativum) modulates gut microbiota and health status of tilapia (Oreochromis niloticus) against Streptococcus iniae infection

This study was conducted to characterize the causative agent of streptococcosis in tilapia (Oreochromis niloticus) and control of Streptococcus infection by means of garlic (Allium sativum) supplementation. The morphological, biochemical and polymerase chain reaction amplification confirmed 11 isolates belong to Streptococcus iniae from the infected fish eyes and tissue samples. Random screening of 12 well‐known medicinal plant parts against S. iniae revealed the garlic extract as the most effective herbal recovery against Streptococcus infection. In vivo challenge test with dietary supplementation of garlic powder significantly improved survival rates of fish against S. iniae infections, and modulate the microbial community and cytokine gene expression profiling in the intestine of the experimental tilapia. Among the two garlic supplemented treatments, 1.0 g garlic supplemented diet significantly increased (p < 0.05) the survival rates of tilapia and the gut bacterial operational transitional units abundance for Proteobacteria and Tenericutes, the phyla associated with healthy intestinal flora. The bacterial diversity index also found high with garlic supplemented diets. Significant upregulations of IL‐10 and IL‐17F gene expression in the intestinal tissue were observed with 1.0 g garlic supplemented diet where IL‐8 and IL‐1β expression levels were relatively static. The dietary supplementation of garlic, therefore, could be effective in the prevention of S. iniae infection in fish.     

Dietary Protein Requirements of Juvenile Black Sea Bass,Centropristis striata

A feeding trial was conducted in a recirculating system to determine the dietary protein requirement for juvenile black sea bass. Six isocaloric diets were formulated to contain varying levels of crude protein (CP) ranging from 36 to 56% (36, 40, 44, 48, 52, and 56%) by substituting a mixture of carbohydrates and lipid for fish meal. The feeding experiment was carried out in 18‐75 L aquaria stocked at a density of 15 juveniles (initial average weight 6.7 g) per tank. Fish were fed test diets in triplicate tanks to apparent satiation twice a day for 8 wk. Whole‐body proximate composition was analyzed after the feeding trial. After the feeding trial, weight gain and specific growth rate of fish fed the 44% CP diet were not significantly different from those fed the 48, 52, and 56% CP diets, but were significantly higher (P < 0.05) than those fed the 36 and 40% CP diets. Feed conversion efficiency and protein efficiency ratio were significantly affected by dietary protein level. The dietary requirement of protein for maximum growth of black sea bass juveniles, estimated using broken‐line regression analysis on weight gain, was 45.3% and maximum weight gain occurred at 52.6% based on polynomial regression analysis.     

Pig manure digestate-derived biochar for soil management and crop cultivation in heavy metals contaminated soil

Management of heavy metal-contaminated soil under drought and other harsh hydrological conditions is critical for protecting soil ecosystem services. In this study, we examined the effect of pig manure digestate-derived biochar as a soil amendment (15 t ha⁻¹) with N fertilizer (180 kg ha⁻¹) on soil and plant heavy metal levels and nutrient availability under various moisture regimes (optimal moisture ~15%, drought condition ≤5%, and flooded condition ≥35% wt.). It was observed that biochar applications significantly decreased heavy metals in the spring wheat plants, lowering Cr by 90%, Ni by 50%, Cd by 9% and Pb by 34% compared to non-biochar (control) treatments. However, the pig digestate-derived biochar increased heavy metals in soil under all moisture regimes, increasing soil Cr by 21%, Ni by 43%, Cu by 55%, Zn by 70%, and Pb by 12%. The availability of macroelements also increased with the biochar applications under the optimum moisture regimes in both soil and plants, increasing Mg²⁺ by 11%, P by 4%, K⁺ by 50%, and Ca²⁺ by 56% in the soil, and Mg²⁺ by 13%, P by 69%, K⁺ by 29, and Ca²⁺ by 39% in plants. Biochar addition also improved chlorophyll fluorescence (CF) levels in the crop for the entire season (12^th to 62^nd day) and the aboveground crop biomass and dry matter contents both increased. Consequently, the use of pig manure digestate-derived biochar with N fertilizer under normal moisture conditions was able to reduce heavy metal availability to plants and thus could be used in contaminated soils to maintain better crop growth and development.