Digestive Enzyme Activity as a Biological Indicator for Assessing the Sustainability of Biofloc and Non-Biofloc Systems in the Nile Tilapia (Oreochromis niloticus) Culture

Removing nutrients in recirculating aquaculture system wastewater from Nile tilapia culture via Spirulina cultivation: Optimizing sodium bicarbonate concentration and micronutrient supplementation

Economic profitability of Nile tilapia production in Kenya was analysed using a model that simulated individual fish growth and took fish population dynamics in the pond into account. The results suggest that the currently practiced mixed-sex tilapia culture is economically unsustainable. It is suggested that research and extension efforts be geared towards developing monosex Nile tilapia production systems. Nile tilapia culture with African catfish predation should be viewed as an intermediate step towards all-male Nile tilapia culture. This will allow accumulation of both physical and human capital to support all-male tilapia culture. Under all-male culture, economic returns are high enough to justify investment in Nile tilapia culture using borrowed capital. However, the success of monosex culture will depend on the availability and affordability of quality fingerlings and low-cost fish feeds. The results have a wide application in Sub-Saharan Africa where mixed-sex Nile tilapia culture is common.

. Effects of stocking density on water quality and on the growth, survival and food conversion of Oreochromis niloticus (Linnaeus) were evaluated. Fingerlings of tilapia (average weight 40.25 ± 94 g) were stocked in six 3.75-m3 concrete tanks at 16, 32 and 42.6/m3 and reared for 164 days. A water flow rate of 1 l/min/kg fish biomass was maintained in all the tanks. The growth rate was inversely related to stocking density with mean weights of 337.25g, 327.0g and 323.5g at the low, medium and high densities respectively. At harvest, standing crop biomass averaged 5.36 kg, 10.44kg and 13.24kg for the three densities. The respective food conversion ratios (FCR) were 1.85, 1.88 and 1.95, while the survival rates were 99.2, 99.6 and 95.9%. However, the survival rate, growth rate and food conversion efficiencies were not significantly different at the three stocking densities. Water quality did not deteriorate in different tanks as the oxygen was continuously replenished and metabolites and waste products removed by the water flowing through the tanks. These data suggest that culture of tilapia at a density of 42.6/m3 and production of 13.24 kg/m3 in 164 days with a production of 18–20 kg/m3 in a growing season (April-October) of 210 days is possible using the drainage water in flow-through water systems.

Avian herbivores face the exceptional challenge of digesting recalcitrant plant material while under the selective pressure to reduce gut mass as an adaptation for flight. One mechanism by which avian herbivores may overcome this challenge is to maintain high activities of intestinal enzymes that facilitate the digestion and absorption of nutrients. However, previous studies in herbivorous animals provide equivocal evidence as to how activities of digestive enzymes may be adapted to herbivorous diets. For example, “rate-maximizing” herbivores generally exhibit rapid digesta transit times and high activities of digestive enzymes. Conversely, “yield-maximizing” herbivores utilize long gut retention times and express lower activities of digestive enzymes. Here, we investigated the activities of digestive enzymes (maltase, sucrase, aminopeptidase-N) in the guts of herbivorous grouse (Aves: Tetraoninae) and compared them to activities measured in several other avian species. We found that several grouse species exhibit activities of enzymes that are dramatically lower than those measured in other birds. We propose that grouse may use a “yield-maximizing” strategy of digestion, which is characterized by relatively long gut retention times and generally lower enzyme activities. These low activities of intestinal digestive enzyme could have ecological and evolutionary consequences, as grouse regularly consume plants with compounds known to inhibit digestive enzymes. However, more comprehensive studies on passage rates, digestibility, and microbial contributions will be necessary to understand the full process of digestion in herbivorous birds.

In relation to mRNA expressions, digestive and hepatic enzyme activity, growth performances of O. niloticus (6.07±0.07) was evaluated after feeding 56 days. Fish were fed six (6) experimental diets where fish oil (FO) supplements dietary oils; virgin coconut oil (VO) {3%FO+3%VO; FVO}, and corn oil (CO) {3%FO+3%CO; FCO}, 6%VO (VO), 6%CO (CO) and 6%VCO {3%VO+3%CO; VCO}. Those fed FCO recorded higher WG (1334.10±5.53) and SGR (4.76±0.01). Muscle lipid was significantly higher in group VO than CO and VCO whereas, it was significantly lower in the liver than the control group (P˂0.05). Dietary alternatives influenced digestive activities (amylase, lipase and trypsin) of which significant differences were not obtained between sections. Digestive enzymes lipase and pepsin were not significantly different at the posterior intestine. Liver receptors (FABP4 and PPAR-α) involved in fatty acid (FA) transport was not influenced, unlike CD36, G6PD and 6PGD. Although, the expression of PPAR-α gene was not different between groups, with the exception of group VCO, all other groups had no significant difference in expression levels of CD36, G6PD and 6PGD unlike FABP4. The study confirms that dietary vegetable lipids in partial replacement improve growth performances and maintain fish physiological functioning with preferences for utilization of 18: 3n-3 and 18: n-n9. Enzyme activity also positively correlates with growth rates and indicates good lipid metabolic activities and retention. As such, dietary alternatives influence liver enzyme activity and their mRNA expressions.

The influence of water salinity on the culture of Nile tilapia with biofloc was evaluated using indicators of water quality, zootechnical performance and animal welfare. Five treatments of different salinities were adopted (0, 4, 8, 12 and 16 g L-1) with three replications. The tilapia were cultured for 90 days and stocked in glass fiber tanks (800 L) at a density of 30 fish m-3 with a mean initial weight of 93.8 ± 0.89 g. Water temperature, chlorophyll-a, sedimentable solids and total suspended solids showed no difference between salinities (p>0.05). The levels of total ammonia nitrogen (3.94 mg L-1) and nitrite nitrogen (0.82 mg L-1) were lower at the salinity of 0 g L-1 compared to the highest salinity (16 g L-1) (p≤0.05). The final weight ranged from 256 to 280 g, with a survival rate of 97 to 100% (p>0.05), which resulted in a productivity of 7.4 to 8.4 kg m-3 (p≤0.05). Glucose was above the baseline value (≤ 60 mg.dL-1) in the 16 gL-1 treatment (76 mg dL-1), and fish growth at the salinities of 8 and 12 g L-1 showed positive allometry (3.020) compared to the other treatments. This demonstrated that it was possible to culture Nile tilapia at salinities of up to 16 g L-1, without compromising performance.

Prolific breeding and production of high percentage of recruits are main problems in mixed-sex Nile tilapia (Oreochromis niloticus) culture in earthen ponds. The current study assessed the efficiency of different sizes of African sharptooth catfish (Clarias gariepinus) in controlling recruitment in mixed-sex Nile tilapia cultured in tanks and its effect on growth performance, percentage survival and yield. Three treatments consisting of triplicate ponds stocked with mixed-sex Nile tilapia in monoculture and in polyculture with large (62.50 ± 3.26 g) and small (40.00 ± 2.68 g) African sharptooth catfish were fed on a 297.50 g kg−1 crude protein diet for 126 days. Results showed that, the number of recruits was significantly lower in larger African sharptooth catfish predator than smaller ones and monoculture of Nile tilapia. Polyculture with larger African sharptooth catfish resulted in significantly higher growth performance of Nile tilapia. Large African sharptooth catfish in polyculture reduced the amount of small, low-value recruits, while the yield of large and high value Nile tilapia was increased. This study revealed that fish farmers can reduce prolific breeding, obtain higher growth performance and produce larger size of marketable Nile tilapia by predominantly stocking ponds with large African sharptooth catfish predator of at least 60 g.

Effects of fermented corn cob on growth performance, digestive enzyme, immune response, and gene expression of nile tilapia (Oreochromis niloticus) raised in biofloc system.

With the increasing occurrence of dietary lead (Pb) contamination in aquatic environment, threat of the dietary Pb toxicity to aquatic organisms attracted more attention. In this study, after being exposed to dietary Pb at concentrations of 0, 100, 400, and 800-microg/g dry weight for 60 days, the groups of tilapia (Oreochromis niloticus) were sacrificed and sampled to analyze the effects of dietary Pb on accumulation, histopathology, and digestive enzyme activities in tissues of the digestive system. The results showed that the Pb accumulation in tissues increased with the dietary Pb concentrations. Moreover, Pb accumulated in sampled tissues in the following order: intestine > stomach > liver. By observation of liver histological sections in optical microscope, lesions could be detected in the Pb-contaminated groups. It was also demonstrated that the inhibitory effect of dietary Pb on digestive enzyme activities was dietary Pb concentration dependent. Different degrees of inhibition of enzyme activities were exhibited in sampled tissues. It was indicated that digestive enzyme activities in the digestive system might be considered as the potential biomarkers of dietary Pb contamination in tilapia.

The effects of composting on the nutritional composition of fibrous bio-regenerative life support systems (BLSS) plant waste residues and its impact on the growth of Nile tilapia ( Oreochromis niloticus)

A 10 week feeding trial was conducted to evaluate the potential effects of ginger powder (GP) and ginger extract nanoparticles (GNPs) on the growth parameters, digestive enzymes (lipase and amylase) activities, blood hematology, blood biochemical indices, immune indices (interleukin 10, immunoglobulin M, nitric oxide, and lysozymes), antioxidant activity, histological characteristics of kidney, spleen, liver, and intestine, and resistance to Aeromonas hydrophila or Pseudomonas putida infection in Nile tilapia, Oreochromis niloticus. Fish (n = 225, 27.01 ± 0.15 g) were stocked in 15 glass tanks (50 × 40 × 60 cm) and randomly allocated to five experimental treatments (TRTs) in triplicate (15 fish/replicate, 45 fish/TRT), consisting of five isocaloric–isonitrogenous diets. The treatments comprised the basal diet (1) without any additives (control group, CON), (2) with 0.5% GP (GP0.5), (3) with 1% GP (GP1), (4) with 0.5% GNPs (GNPs0.5), and (5) with 1% GNPs (GNPs1). Fish were manually fed to satiety three times a day (at 9 a.m., 12 p.m., and 2 p.m.). Fish were weighed at the start of the experiment, then the body weight, weight gain, feed intake, and feed conversion ratio were determined at the end of the experiment. At the end of the feeding period, 15 fish/TRT were intraperitoneally inoculated with two pathogenic bacterial strains (A. hydrophila or P. putida) in two separate challenge tests. Blood samples were collected from each TRT at two aliquots for hematological and biochemical analysis at the end of the feeding period. A significant improvement in fish growth was observed in GP and GNPs TRTs compared to the control group. There were no significant changes in the total amount of feed intake/fish in response to the experimental diets. Diets enriched with GNPs, particularly the GNPs1 TRT, resulted in a significant increase (p < 0.05) in digestive enzyme activity (lipase and amylase), serum growth hormone level, proteinogram, and immune indices (lysozyme, immunoglobulin M, interleukin 10, and nitric oxide). In addition, a significant increase in hepatic antioxidant enzymes (superoxide dismutase, reduced glutathione, and catalase) was observed in fish fed with GNPs-enriched diets. Survival percentages following bacterial challenge were higher in GNPs1, followed by GP1 and GNPs0.5 TRTs. Normal histomorphology was found in liver, kidney, and spleen tissues in all experimental TRTs. We conclude that GP and GNPs could be included in Nile tilapia diets for promoting fish growth, immunity, antioxidant status, and disease resistance without harming organ functions. In particular, the most effective treatment was GNPs1.

Fermented food waste for culturing jade perch and Nile tilapia: Growth performance and health risk assessment based on metal/loids

Effects of diet containing germinated faba bean (Vicia faba L.) on the intestinal health and gut microbial communities of Nile tilapia (Oreochromis niloticus)

In order to evaluate the interplay of nutritional status and the digestive capacity, immune function, and gut microbiota in the oriental river prawn Macrobrachium nipponense, a 14-day starvation trial was conducted to detect the effects of starvation on the activities of digestive enzymes and immune enzymes and the structure of prawn gut microbiota. The adult prawns were randomly assigned to a control group (F group) and starvation group (S group) with three replicates. The F group was normally fed with commercial diet, and the S group was starved for 14 days. The result showed that digestive enzyme activities of trypsin and lipase in the hepatopancreas of the S group were significantly lower than those of the F group after 4 d of starvation ( P < 0.05 ), while the activity of amylase significantly increased after 14 d of starvation ( P < 0.05 ). Moreover, the results of the histological analysis of prawn gut showed that both the height of epithelial cells and microvilli of intestine in the S group were obviously decreased than those in the F group ( P < 0.05 ) after 14 d of starvation. The activities of immune-related enzymes including superoxide dismutase, catalase, and acid phosphatase in the hepatopancreas of the S group significantly decreased after 4 d of starvation, and lysozyme activity of the F group was lower than that of the S group after 7 d of starvation ( P < 0.05 ). In addition, the results of Illumina high-throughput sequencing showed that a total of 14,285 OTUs were obtained and classified into 30 phyla, among which Actinobacteria and Proteobacteria were the predominant microflora in the intestinal microbial communities of both groups. However, the relative abundance of opportunistic pathogens was significantly increased in the S group, while the relative abundance of beneficial bacterium was decreased ( P < 0.05 ). The bacterial richness with the Chao estimator was significantly higher in the F group than in the S group ( P < 0.05 ). Both the results of principal coordinate analysis (PCoA) and nonmetric multidimensional scaling (NMDS) demonstrated that the intestinal microbiota of the F group was separate from those of the S group. The result of functional prediction of the metabolic pathways showed that the intestinal microbiota was enriched in the KEGG pathways of amino acid, carbohydrate, fatty acid, and lipid biosynthesis and degradation at level 2. This result implied that the microbiota of shrimp gut decreased nutrition metabolism under the stress of starvation. Meanwhile, comparing to the F group, the immune-related pathway of enterobacterial common antigen biosynthesis was markedly reduced in the S group ( P < 0.05 ). The result of redundancy analysis (RDA) further confirmed that the activities of digestive and immune enzymes were correlated with the microbial community structure. Finally, the structural equation modeling highlighted that changes in the activities of digestive and immune enzymes were directly related to the gut bacterial community and notably affected prawn growth.

The objective of this study was to evaluate the effect of different feed management on the quality of effluent water generated in Nile tilapia (Oreochromis niloticus) culture ponds. Feed was supplied as follows: natural food, and pelleted, extruded or minced ration. The study was conducted during 19 weeks in 12 continuous water exchange ponds of 300 m² each, with a population of male Nile tilapia juveniles, in a density equal to 1.7 fish m-2. Feeds contained 30% crude protein, 3,000 kcal digestible energy, and were supplied twice a day. Natural food consisted of chicken manure. Temperature, dissolved oxygen, pH, total phosphorus, total nitrogen, chlorophyll a and suspended solids were monitored weekly in the supplying and effluent water. Water residence time was also determined for the ponds. In general, effluent water quality decreased in all treatments.