The effects of partially substituting Indian carps or adding silver carp on polycultures including small indigenous fish species (SIS)

A sustainable semi-intensive pond aquaculture technology including major carp species (Indian, Chinese and common carp) as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized in Bangladesh. Silver carp inclusion in the polyculture is now being considered, because this very efficient filter feeder has a strong impact on pond ecology and also on the farmers' family nutrition because it is a cheap fish that the family can afford to eat instead of selling. The present paper is centered on the reduction of silver carp negative effects on other species while keeping the advantages of increased total yield and income due to silver carp stocking. It presents the results of two experiments, one on-station and one on-farm, in which 3–5 silver carp/100 m² were added or partially substituted major carp filter feeders. The basic stocking density was 100 carps (rohu, catla and a bottom feeder, either mrigal or common carp, at a 1:1:1 ratio) and 250 SIS (punti and mola) per 100 m². In the on-station experiment silver carp density was 3 and 5 fish/100 m² and the large carp bottom feeder was common carp. In the on-farm experiment silver carp density was 5 fish/100 m² and the bottom feeder was either common carp or mrigal.Most of the water quality and fish performance parameters tested were not affected by the polyculture composition. Adding 3–5% silver carp or substituting 3–5% of the herbivorous fish species by this highly efficient filter feeder increased grazing pressure on the phytoplankton, which led to a 25–40% reduction of the chlorophyll concentration in the water column. The increased grazing pressure was not enough to affect other water quality parameters and fewer effects on the availability of food for the other fish species occurred than when the silver carp addition was 10% of the polyculture, as reported in a previous work. The strong negative effects of silver carp on the other species of the polyculture and the higher total yields and income recorded in previous experiments with the addition of 10 silver carp/100 m² were much weaker and their expression depended on other pond conditions when 3 or 5 silver carp/100 m² were added or substituted the same number of rohu or catla, either when the bottom feeder was mrigal or common carp. It was concluded that stocking 3 silver carp/100 m² over the usual 100 large carp and 250 SIS /100 m² can be considered a ‘no effect’ stocking density in relation to the control without silver carp, while stocking 10 silver carp/100 m² should be preferred by farmers to keep the option of selling or consuming the silver carp.     

Comparison of rice straw and bamboo stick substrates in periphyton-based carp polyculture systems

An experiment was conducted to compare rice straw mat and kanchi (bamboo sticks) as substrates in periphyton‐based polyculture systems. The experiment had three treatments: (a) no substrate (control), (b) rice straw as a substrate (3 × 2.7 kg pond^?1) and (c) kanchi as a substrate (390 kanchi pond^?1). Fingerlings (n=40) of rohu, Labeo rohita (24.5±0.5 g); mrigal, Cirrhinus mrigala (25.1±0.6 g); catla, Catla catla (25.8±0.5 g); common carp, Cyprinus carpio (27.6±0.6 g), and silver carp, Hypophthalmichthys molitrix (30.4±0.9 g) were stocked at a 3:2:2:2:1 ratio and cultured for 90 days. There were no differences in the number of plankton, periphyton and macro‐zoobenthos among the treatments. The total plate count of bacteria was higher in the rice straw treatment (41 320 million cfu m^?2) than that in the kanchi treatment (11 780 million cfu m^?2). Growth and the final mean weight of rohu, catla and common carp were higher in the substrate treatments than those in the control. Rice straw and kanchi treatment, respectively, resulted in 38% and 47% higher combined total weight gain over control. Gross margin analysis showed that rice straw treatment resulted in more profit than the control and kanchi treatment. Therefore, rice straw has the potential to be used to increase production in the low‐input rural aquaculture.     

Effects of tilapia (Oreochromis niloticus L.) stocking and artificial feeding on water quality and production in rohu–common carp bi‐culture ponds

Previous research showed that stocking 1.5 rohu (Labeo rohita) and 0.5 common carp (Cyprinus carpio) m⁻² yields the highest production in small holder ponds in Bangladesh. The present study looked into the effects of additional stocking of Nile tilapia (Oreochromis nilotica) in fed or non‐fed ponds on water quality and fish production. A low, additional stocking density of 0.2 Nile tilapia m⁻² was tested. All treatments were executed in triplicate in 100 m² ponds and the duration of the experiment was 4.5 months. The results showed that tilapia addition increased nutrient concentrations and reduced total suspended solid concentration and phytoplankton biomass (P<0.05). Tilapia stocking resulted in additional production without affecting the growth and production of rohu and common carp. Supplemental feeding increased the nitrogen and phosphorus concentrations, phytoplankton availability and the growth and production of rohu and common carp (P<0.01). The combination of supplemental feeding and tilapia stocking resulted in a higher net yield than the other treatments (P<0.05). Stocking 1.5 rohu, 0.5 common carp and 0.2 tilapia m⁻² in fed‐ponds is a good culture combination for polyculture farmers in South Asia.     

Effects of day and night on swimming,grazing and social behaviours of rohu Labeo rohita (Hamilton) and common carp Cyprinus carpio (L.) in simulated ponds

Diel rhythmicity of grazing, swimming, resting and social interactions of rohu (Labeo rohita) (weight 66.5–68.3 g) and common carp (Cyprinus carpio) (79.9–82.0 g) were observed in 1 m² simulated ponds using video images. Fish behaviour was monitored during a full 24‐h period, starting at 08:00 hours with a 15‐min recording, which was repeated every 3 h. Rohu spent more time grazing during the day than at night. Grazing activity peaked at the beginning and at the end of the day. Grazing and resting of rohu were negatively correlated. Common carp grazed day and night, showing no distinct grazing peak. Considering the grazing time of rohu and common carp, a feeding schedule with two feeding times at 07:30 and 16:30 hours might be appropriate for better food intake and conversion in rohu–common carp polyculture system.     

Rhizobacteria as bioenhancer and biofertilizer for growth and yield of banana (Musa spp. cv. ‘Berangan’)

Banana, an important fruit crop, requires high amounts of fertilizers for commercial cultivation, which is costly and can be hazardous to the environment when used excessively. Inoculations of plant growth promoting rhizobacteria (PGPR) have been shown to produce beneficial effects through growth stimulation in legumes and cereals, and an attempt has been made to use rhizobacteria in bananas. Three experiments were conducted to observe the effects of plant growth promoting rhizobacteria (PGPR) inoculation on root stimulation and colonization, nutrient absorption, growth and yield of bananas (Musa spp. cv. ‘Berangan’, AA type). The results showed that inoculation together with 33% N improved the bioenhancing activity by increasing root and shoot growth, and photosynthetic rate. The PGPR inoculation with 33% N-fertilizer also increased the Ca uptake capacity resulting in higher Ca concentration in root, corm and pulp but increased the Mg concentration in the root only. In addition, the total accumulation of nutrients was heavily influenced by PGPR inoculation due to enhanced root proliferation. The PGPR inoculation greatly increased the bunch yield (35–51%). The strains Sp7 and UPMB10 were evaluated for their N₂ fixing capacities in association with banana roots by ¹⁵N isotopic dilution technique and acetylene reduction assay (ARA). The results conclusively showed that roots of PGPR-inoculated plants fixed N₂ and produced higher ARA values and inoculated plants together with the least N-fertilizer supply showed the highest amount of nitrogen derived from atmosphere (Ndfa). The findings from the above studies demonstrated that PGPR strains (Sp7 and UPMB 10) inoculation with minimal N-fertilizer supply are effective as a bioenhancer for increasing plant growth, nutrient uptake and yield of bananas.     

Effects of selective harvesting and claw ablation of all‐male freshwater prawn (Macrobrachium rosenbergii ) on water quality,production and economics in polyculture ponds

The effects of selective harvesting (SH) and claw ablation (CA) of blue‐clawed (BC) prawns on an all‐male freshwater prawn–finfish polyculture system were compared with control (Co) in quadruplicate. Ponds were stocked with all‐male freshwater prawn Macrobrachium rosenbergii, silver carp Hypophthalmichthys molitrix, catla Catla catla and mola Amblypharyngodon mola at 12 000, 2000, 500 and 20 000 ha^?1 respectively. Prawns were fed with pelleted feed. Ponds were fertilized regularly with urea, triple super phosphate and cow‐dung. SH of BC prawns in treatment SH and CA in treatment CA started on the 60th day during a 137‐day culture and continued at 15‐day intervals until the final harvest. Water quality parameters and plankton abundance did not vary significantly (P>0.05) among the treatments. Treatment SH resulted in a higher (P<0.05) net production of freshwater prawn (437 kg ha^?1), with better survival and mean weight, followed by CA (354 kg ha^?1) and Co (322 kg ha^?1). The combined net production of prawn plus finfish was also higher in SH (1244 kg ha^?1) as compared with CA (1161 kg ha^?1) and Co (1137 kg ha^?1), although the finfish production did not differ significantly. The periodic SH of BC prawns showed a better economic return with a BCR of 1.71.     

The role of potassium fertilizer in nodulation and nitrogen fixation of faba bean (Vicia faba L.) plants under drought stress

Three-week-old nodulated faba bean plants were subjected to different levels of drought stress (onehalf, one-quarter, or one-eighth field capacity) for 5 weeks. Half the stressed plants were treated with KCl at 10 mg kg^-1 soil or 150 mg kg^-1 soil at the beginning of the drought stress. Nodulation and nitrogenase activity were significantly decreased by increasing drought stress. Leghaemoglobin and protein contents of nodule cytosol were also severely inhibited by drought sttess. This decline was attributed to the induction of protease activity. However, carbohydrate contents of the nodule cytosol increased significantly. This accumulation was attributed to a sharp decline in invertase activity and low use of sugar by the bacteroids We conclude that harmful effects of water deficits can be alleviated by increasing K⁺ supplementation.     

Effects of Different Drying Methods on Some Physical and Chemical Properties of Loquat (Eriobotrya japonica) Fruits

ABSTRACT

In this communication, we have discussed and compared the different drying processes i.e. flat plate solar collector, open sun and mechanical dryer with the preservative solution of Sodium Benzoate. Loquats were pretreated with preservative solution and subject to the drying process. Drying kinetics in terms of moisture lost per hour and drying rate, texture and antioxidants retention were determined before and after drying. Statistical analysis of the data showed that the different drying process has significantly affected on the kinetics of loquat fruits with the confidence interval of (α ≤ 0.05), whereas the preservative solution showed a non-significant effect on texture and antioxidants retention. High moisture lost per hour (5.4%) was recorded in mechanical dryer followed by flat plate solar collector dryer (3.7 %) while minimum (1.8%) was recorded in open sun drying. Good textured dried loquat with optimum hardness (313 g) and stiffness (141 g mm^?1) was found in flat plate solar collector dried samples. Similarly more antioxidants (52%) retained in samples dried with hot air using flat plate solar collector followed by the mechanical dryer (47%) while minimum (41%) was recorded in open sun drying. Although mechanical drying is fast, it does not help to maintain a good texture and more antioxidants. From the study, it was concluded that hot air drying using a flat plate solar collector is better for drying process to get valuable dried loquat with good texture and more antioxidants.     

Effect of ginger (Zingiber officinale Roscoe) on growth performance, nutrient digestibility, serum metabolites, gut morphology, and microflora of growing guinea fowl

A 56-day feeding trial was conducted to investigate the effect of dietary supplementation of dried ginger meal (DGM) on the growth performance, nutrient digestibility, serum parameters, gut morphology, and microflora of growing helmeted guinea fowl (Numidia meleagris). One hundred sixty 28-day-old male keets were assigned to four dietary treatments. There were 40 birds per treatment replicated four times with 10 keets each. The experimental diets consisted of the basal diet (control), ginger-supplemented diets containing 20, 40, and 60 g/kg DGM, respectively. Guinea fowls fed diet supplemented with DGM had higher (P <0.05) final body weight, body weight gain and lower (P <0.05) feed intake. Optimum weight gain was obtained with supplementation level of 36.15-g DGM (R ²?=?0.923). Guinea fowls fed diet supplemented with 40 g/kg DGM recorded the highest (P <0.05) coefficient of total tract apparent digestibility of dry matter, ether extract and longest (P <0.05) duodenal and ileal villus heights. The crypt depth of the duodenum and ileum reduced (P <0.05) with increasing level of dietary supplementation of DGM. Dietary supplementation of DGM resulted in increased (P <0.05) total serum protein, serum albumin and low (P <0.05) serum cholesterol concentration. Ileum content of birds fed diet supplemented with 40 g/kg DGM recorded the highest (P <0.05) lactobacillus count. In conclusion, dietary inclusion of 40-g DGM per kilogram diet is hereby recommended for improved growth, apparent nutrient digestibility, gut morphology, serum chemistry, and stimulation of balanced intestinal microflora in growing guinea fowl.     

Antifungal activity of new 1,3,4-oxadiazolo[3,2-a]-s-triazine-5, 7-diones and their 5-thioxo-7-ones

N(1)- and N(3)-(4-fluorophenyl) ureas (III a-e) were cyclocondensed with ethyl chloroformate and CS(2)/KOH to yield 2-aryl-6-(4-fluorophenyl)-1,3,4-oxadiazolo[3,2-a]-s-triazine-5, 7-diones (IVa-e) and their 5-thioxo-7-ones (Va-e), respectively. The compounds III-V(a-e) have been compared with Dithane M-45 for their fungitoxic action against A. niger and F. oxyporum, and the results have been correlated with the structural features of the tested compounds.