Ammonia is a problematic environmental toxicant for aquatic species. Research results indicate how Yucca schidigera extract (YSE) alleviated the adverse impacts induced by ammonia intoxication in Nile tilapia (Oreochromis niloticus L.) through its effects on growth performance, hemato-biochemical and antioxidant-related parameters, and histopathological changes. In this sense, YSE could be used as a functional water supplement in aquaculture.
Increased demand for fish as a food source is a consequence of pervasive population growth. Fish farming is an ideal potential means of facing the high food and nutrition demands of human beings. However, the intensification of aquaculture in turn causes water pollution, which is consistently related to increased levels of ammonia, and represents about 70% of nitrogenous fish wastes (Boyd, et.al., 2018, De Leão, et al., 2009).
Ammonia induces oxidative stress via the overproduction of ROS (reactive oxygen species), which deteriorates important biomolecules, such as DNA, proteins, lipids, and initiates a cascade of events that causes impairment of cellular functions; among other effects.
There is an urgent need to control aquaculture’s nitrogenous waste deleterious effects to maintain water quality, survivability, and “clean” production systems. Medicinal plants represent an immense source of bioactive constituents that can increase fish performance, antioxidant potential, and immune responses, in addition to alleviating stress conditions.
Numerous studies documented that Yucca schidigera extract (YSE) has antioxidant, growth-promoting, antiinflammatory, immune-stimulatory, and anti-carcinogenic effects in many species such as chickens, Japanese quail, and rabbits. YSE can regulate energy metabolism and hormonal activity in animals.
Nile tilapia (O. niloticus L.) is an important cultured aquaculture species throughout the world that could be used as a suitable model for studying nutrition and metabolism not only because of its rapid growth and high resistance to diseases and toxic stress but also due to the availability of its whole genomic information.
This species also has well-developed digestive and metabolic organs, including liver, muscle, and adipose tissues. To date, little is known about the YSE’s molecular modulatory mechanism against ammonia stress concerning tilapia growth, energy mobilization, and inflammatory response.
Hence, this investigation aimed to declare YSE modulatory effect (s) against chronic ammonia intoxication in Nile Tilapia.
Materials and Methods
A total of 120 healthy male monosex Nile tilapia (O. niloticus) were collected from a private farm “El-Behaira Governorate, Egypt”, with an average body weight of 42.22 ± 1.25 (mean ± SD) initial weight and transported to the Faculty of Aquatic and Fisheries Sciences, Kafrelsheikh University, Egypt. Before the experiment, the fish were acclimated for two weeks.
The fish were then divided into four groups (30 fish per group) in 12 glass aquaria, ten fish per glass aquarium (70 × 40 × 60 cm), and the fish were randomly distributed into four groups.
The first group was kept as a normal control group, the second group exposed to ammonia from the beginning of the experiment for four weeks, the third group was supplied with YSE and exposed to ammonia for four weeks and the fourth group supplied with YSE in water at a dose of 8 mg/L water every two days.
The experimental design is described in Figure 1.
The fish were fed a basal diet prepared according to National Research Council (NRC) (Table 1) that was supplied twice daily (09:00 am and 03:00 pm). YSE (3% saponins, obtained from ANOVA Pharm Company, Tanta, Egypt) was supplied in water at 8 mg/L every two days.
The chemical constituents of the basal diet were confirmed following the standard methods. All the fish were weighed at the beginning of the experiment and every week until the end of the experiment (4 weeks) to readjust the feed intake and visually monitor the fish’s health status.
The wastes were siphoned daily from all aquaria, and water was exchanged with de-chlorinated water, except for the ammonia groups.
Different water parameters were measured on a daily basis throughout the experiment’s duration, including dissolved oxygen (DO), ammonia, water temperature, and pH, in all experimental groups. Different measures and tests were performed
i) Blood Sampling, Hematological and Serum Biochemical Analysis,
ii) Evaluation of Lipid Peroxidation and Antioxidant Enzymes,
iii) Histopathology Study, and
iv) Total RNA Extraction, cDNA Synthesis, and RealTime Quantitative PCR Assay.
Statistical analysis of the data was performed using the one-way ANOVA test followed by Tukey’s post hoc test to determine the difference between the mean values of the different groups. All statistical analyses were performed using GraphPad PRISM software (Version 8.0.2, La Jolla, CA, USA), p-value < 0.05 was considered to indicate statistically significant differences. All data were expressed as Means ± SEM.
Table 2 shows the results for the measurement of parameters of the water quality including the water temperature, pH, DO (dissolved oxygen), TAN (total ammonia nitrogen) and UIA (unionized ammonia), which did not differ among the control group and the YSE-supplied group (p > 0.05).
Moreover, the pH and the levels of TAN, and UIA were significantly (p < 0.05) increased in the fish group exposed to elevated ammonia levels when compared to the control group. However, YSE supplementation significantly reduced (p < 0.05) pH, TAN, and UIA levels compared to the fish group exposed to high ammonia levels. Table 2.
Figure 2 portrays the growth performance of the examined fish groups. The FBW, BWG, and SGR were not significantly changed in the fish group supplied with YSE compared to the control group (p > 0.05).
However, compared to the control group, fish exposed only to high ammonia levels showed significantly lowered FBW (final body weight), BWG (body weight gain) SGR (specific growth rate), and higher FCR (feed conversion ratio).
Conversely, supplying YSE to ammonia-intoxicated fish successfully enhanced FBW, BWG, and SGR and significantly lowered FCR in comparison to the fish group exposed only to high ammonia levels.
Leukogram and Serum Biochemical Findings
Table 3 represents the effects of high levels of ammonia and/or the ameliorating role of YSE in terms of leukogram findings and serum biochemical analysis.
The second fish group, exposed to high ammonia levels, exhibited signs of stress leukogram, which were represented by a significant (p < 0.05) increase in WBCs, heterophil, and monocyte counts, with a decline in lymphocyte and eosinophil counts, compared to the normal control group.
However, YSE administration to ammonia-intoxicated fish restored the values of the stress leukogram to normal reference levels compared to the second fish group, which was intoxicated by high ammonia levels, where no changes occurred.
“Ammonia is a critical hazardous nitrogen metabolic product in aquaculture. Despite trials for its control, ammonia intoxication remains one of the most critical issues to overcome.”
Moreover, ammonia intoxication significantly (p ≤ 0.05) increased the values of serum hepatic biomarkers ALT, AST, and LDH enzyme activities, and renal injury markers such as BUN with increased glucose levels, while declines occurred in serum parameters such as total proteins (TP), albumin, TC, TG, HDL-C, and VLDL-C, mylase and lipase.
Conversely, YSE resulted in an effective improvement according to the measurement of ammonia-altered hepatorenal injury markers. Notably, there were no significant alterations in serum biomarkers in fish supplied with YSE alone when compared to the control fish group, indicating the safety of YSE at the selected dose used in the current study.
Hepatic Lipid Peroxidation and Antioxidant Biomarkers
Figure 3 elucidates the impacts of the elevated ammonia level as well as the beneficial effects of YSE on the elucidation of hepatic lipid peroxidation and antioxidant parameters.
The fish group exposed to high ammonia levels revealed a significant (p ≤ 0.05) increase in hepatic MDA level with a significant (p ≤ 0.05) depletion of hepatic GPx, SOD enzyme activities and GSH contents compared with the control fish group.
However, the findings of ammonia-intoxicated fish additionally supplied with YSE were opposed to the findings for the ammonia-intoxicated group, in which there was an inhibition of hepatic MDA content, and an enhancement of SOD, GPx enzyme activities, and GSH levels. Figure 3.
Figure 4 shows that ammonia intoxication induced marked degenerative and necrotic changes within the hepatopancreas (P) with a moderate degree of hepatic vacuolation (Figure 4B). However, YSE treatment markedly improved pathological changes in the hepatopancreas that were induced by high ammonia levels (Figure 4C).
Moreover, melanomacrophage centers (MMC) in which macrophage aggregates contain distinctive groupings of pigment-secreting cells within the tissues of heterothermic vertebrates were markedly depleted in the ammonia-intoxicated group (Figure 4F).
On the other hand, YSE treatment to ammonia-intoxicated fish had improved the MMC (Figure 4G). Moreover, brain sections in the second group showed a wide area of malacia associated with marked gliosis (Figure 4J). However, the administration of YSE to ammonia-intoxicated fish resulted in tiny foci of malacia with a marked decrease in gliosis (Figure 4K).
Additionally, an elevated ammonia level induced severe loss of secondary lamellae with marked infiltration of inflammatory cells (Figure 4O), while YSE treatment resulted in a marked decrease in the adhesion between the secondary lamellae (Figure 4N).
Relative Gene Expression of Appetite- and Growth-Related Genes
Figure 5 represents the effects of high ammonia levels and/or YSE on the relative mRNA levels of the brain NPY, liver IGF-1, MSTN, and brain MSTN.
Compared with the control group, the second fish group, which was intoxicated by ammonia, had reduced levels of both brain NPY (Figure 5A1, A2) and hepatic IGF1 (Figure 5B1, B2) after two and four weeks, respectively, and brain MSTN after two weeks only (Figure 5D1), and elevated MSTN gene expression levels were found in both the liver (Figure 5C1, C2) and the brain (Figure 5D2) after four weeks.
On the other hand, the fish group supplied with YSE and intoxicated with ammonia (3rd group) exhibited higher expression levels of brain NPY (Figure 5A1, A2) and hepatic IGF1 (Figure 5B1, B2) with a decreased expression of liver MSTN (Figure 5C1, C2) after two and four weeks, and brain MSTN (Figure 5D2) after four weeks, compared with the chronically intoxicated ammonia group.
The results provided a novel perspective on the multiple interacting mechanisms through which YSE may exert its protective role against chronic ammonia toxicity. These findings affirmed the growth-enhancing effects of YSE via the sustained enhancement of food intake, the elevation of IGF-1, the suppression of hepatic and brain MTSN expression levels, and the restoration of carbohydrate and lipid reserves, mediated through alterations in the levels of circulating metabolites.
YSE alleviated the adverse impacts induced by ammonia intoxication through its ability to scavenge free radicals, potent antioxidant activities, and anti-inflammatory properties. YSE supplementation was beneficial for both health and growth in Nile tilapia, and it could be used as a functional water supplement in aquaculture.
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This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “EXPLORING THE MULTIMODAL ROLE OF YUCCA SCHIDIGERA EXTRACT IN PROTECTION AGAINST CHRONIC AMMONIA EXPOSURE TARGETING: GROWTH, METABOLIC, STRESS AND INFLAMMATORY RESPONSES IN NILE TILAPIA (OREOCHROMIS NILOTICUS L.)” developed by ZIZY I. ELBIALY – Kafrelsheikh University; ABDALLAH S. SALAH – Kafrelsheikh University; AHMED ELSHESHTAWY – Kafrelsheikh University and University of Stirling ; MERNA RIZK – Kafrelsheikh University; MUYASSAR H. ABUALREESH – King AbdulAziz University; MOHAMED M. ABDEL-DAIM – King Saud University and Suez Canal University; SHIMAA M. R. SALEM – Mansoura University; AHMAD EL ASKARY Taif University; and DOAA H. ASSAR – Kafrelsheikh University.
The original article was published in Animals, in July 2021.
The full version can be accessed freely online through this link https://doi.org/10.3390/ani11072072