Static Bioassay Research Articles

Acute toxicity of chlorpyrifos to some non-target freshwater organisms: which one is more toxic-technical grade or commercial formulation?

Chlorpyrifos is among the most widely sold organophosphates in the agriculture sector worldwide. Static bioassays were performed in the laboratory to compare the acute toxicity between the technical grade (94% a.i.) and commercial formulation (20% EC) of chlorpyrifos to four freshwater organisms: the crustacean zooplankton Cyclops viridis, the oligochaete worm Branchiura sowerbyi, the gastropod Pila globosa, and tadpole larvae of Duttaphrynus melanostictus. The recovery of actual chlorpyrifos concentrations in water after 2 h of exposure to the nominal concentrations ranged from 82.98% to 88.56%. The commercial formulation (F) of chlorpyrifos was found to be 1.94 to 2.76 times more toxic than the technical grade (T). Based on 96 h LC50 values of T and F chlorpyrifos, C. viridis was found to be most sensitive (0.56 and 0.25 μg/L) and P. globosa as most tolerant (1482 and 536 μg/L) to chlorpyrifos. Changes in LC50 values of both T and F chlorpyrifos were noted in respect of exposure hours for the three aquatic invertebrates and the tadpole larvae of the toad. In conclusion, the acute toxicity of chlorpyrifos to some non-target freshwater organisms differs between technical grade and commercial formulations.

TOXICITY AND HAEMATOLOGICAL CHANGES OF Datura innoxia STEM ON Clarias gariepinus JUVENILES

The acute toxicity and haematological changes of Datura innoxia stem on Clarias gariepinus juveniles was investigated in a static bioassay to determine the Median Lethal concentrations (LC50) at 96 hrs of exposure. Six graded concentrations of 0, 320, 330,340, 350 and 360mg/l of the aqueous extract were applied to C. gariepinus juveniles in plastic bowls. The result obtained revealed the 96hrs LC50 values to be 86.67mg/l with an 87% confidence interval between the lower and higher limits of 320 and 360mg/l. Fish exposed to acute toxicity test exhibited several abnormal behaviours, including air gulping/gasping, erratic swimming, discolouration haemorrhage, loss of reflex and molting were observed at the bottom of the bowl just before death The oxygen consumption by juveniles decreased with increased concentrations of Datura innoxia stem extract. The packed cell volume (31.34-34.78%), the red blood cell counts (1.75-2.01), haemoglobin (9.03-11.12g/dl) and mean corpuscular haemoglobin concentration were significantly depleted while, white blood cell counts (6.05-7.21) significantly decreases as the concentrations of Datura innoxia stem extract increases. The implication of these findings revealed that the stem of D. innoxia stem have negative effects on the test fish. The toxic effect of Datura innoxia stem on Clarias gariepinus juveniles were both time (12hrs) and dose dependent (340mg/l). It was concluded that Datura innoxia stem are harmful to Clarias gariepinus juveniles with significant haematological alterations.

Acute toxicity of Oreochromis niloticus fingerlings exposed to effluent from Delta State University, Abraka Nigeria boys hostel

Studies on aquatic pollution are crucial for maintaining environmental health. This study assessed the toxicity of effluents from the male hostel site II at Delta State University (DELSU) on Oreochromis niloticus fingerlings. Behavioral responses and mortality rates were observed as toxicity indicators. The physicochemical characteristics of the raw effluent were evaluated and compared with standard methods. In a 96-hour static bioassay, 20 fingerlings were exposed to varying effluent concentrations: 0%, 20%, 40%, 60%, 80%, and 100%, with the experiment triplicated. Analysis showed pH (5.6), temperature (26.1°C), TDS (304 mg/L), dissolved oxygen (5.7 mg/L), chlorine (5.55 mg/L), ammonia (0.21 mg/L), and hardness (0.79 mg/L). Water analysis over 12-96 hours ranged for pH (5.45-5.62), temperature (22.50-26.30°C), TDS (61.50-237.50 mg/L), DO (4.45-6.00 mg/L), chlorine (0.84-3.98 mg/L), ammonia (0.14-0.37 mg/L), and hardness (6.52-31.93 mg/L), with no statistically significant differences (p>0.05). Behavioral responses included air gulping, irregular swimming, and lack of reflex. Mortality depended on effluent concentration, with no deaths at 0%-80% but 80% mortality at 100%. Lethal times for 50% and 95% mortality at 100% concentration were 48.6 and 102.8 hours, respectively. Diluting or treating wastewater before release is necessary to prevent fish mortality in the wild.

Comparative Acute Toxicity Studies of Chlorpyrifos Technical Grade with its Emulsifiable Concentrate (20% EC) on Labeo rohita, a Freshwater Major Carp, and Mystus vittatus, a Freshwater Catfish.

Chlorpyrifos is widely used across the world as an organophosphate insecticide and frequently contaminates freshwater bodies through runoff from agricultural fields. In the laboratory, static bioassays were undertaken to examine differences in acute toxicity caused by exposure to the technical grade (94% a.i.) and an emulsifiable concentrate (20% EC) of chlorpyrifos to two species of freshwater fish, Labeo rohita and Mystus vittatus. The recovery of actual chlorpyrifos concentrations varied from 83% (technical grade, T) to 89% (emulsifiable concentrate, F) after two hours in water. The susceptibilities of the two fish species to the two types of chlorpyrifos varied. The 96-h LC50 values for T and F chlorpyrifos in L. rohita were 68 and 36µg/L, respectively, and 120 and 62µg/L in M. vittatus, respectively. As the exposure period was extended, the LC50 values gradually decreased. LC50 values between the technical grade and formulation were compared following the criteria of Mayer et al. (1986), Schmuck et al. (1994), APHA (1995), and Demetrio et al. (2014). It was concluded from the study that the emulsifiable concentrate (20% EC) of chlorpyrifos was more toxic than technical-grade chlorpyrifos.

Evaluation of Acute Toxicity and Lethal Concentration (LC50) of Cypermethrin (25% EC) in Adults of Cyprinus carpio (Linnaeus 1758)

The present study attempted to determine the acute toxicity and medial lethal concentrations of Cypermethrin (25% EC) for common carp Cyprinus carpio using Finney’s static bioassay (1971), probit analysis method. The LC50 values for 24, 48, 72 and 96 hr were found to be 3.962 µl Lit-1, 3.767 µl Lit-1, 3.349 µl Lit-1 and 2.924 µl Lit-1 respectively. Fish (weight 90–100 g, length up to 18±2 cm) were exposed to different concentrations of cypermethrin which were 1.5 µl Lit-1, 2.0 µl Lit-1, 2.5 µl Lit-1, 3.0 µl Lit-1, 3.5 µl Lit-1, 4.0 µl Lit-1 and 4.5 µl Lit-1 up to 96 hr. LC50 value decreases with an increase in exposure time. During this exposure period, abnormal behaviors like restlessness, hyperactivity, erratic movements, increased opercular movements, and loss of equilibrium and response were noticed in carp. Over secretion of mucous all over the body surface along with respiratory stress and mortality was also observed.

Comparison of the acute toxicity and behavioural effects of two pyrethroids on African catfish Clarias gariepinus fingerlings

Two of the most-commonly used pyrethroid insecticides were subjected to static bioassays to determine their acute toxicity to Clarias gariepinus fingerlings, followed by comparisons of their impact on mortality and behavioural changes in the fish. The LC50 values for deltamethrin (DMT) at exposure durations of 24, 48 and 96 h were 12, 9 and 8 µg l−1, respectively; the LC50 values for cypermethrin (CYP) at the same exposure durations were 55, 44 and 26 µg l−1, respectively. The estimated safe limits ranged from 8×10−1 to 8×10−5 µg l−1 for DMT, and 26×10−1 to 26×10−5 µg l-1 for CYP. The tested substances had an acute toxicity effect on fish development as they caused death, and chronic toxicity effects as they changed fish behaviour. Fish exposed to either one of these pesticides showed behavioural alterations, such as loss of static balance, excessive mucous secretion, irregular swimming, gulping of air and skin discolouration. The results reveal that CYP was less toxic (96-h LC50 = 26 µg l−1) than DMT (96-h LC50 = 8 µg l−1) based on the greater LC50 value and a lower percentage of mortality. To avoid potential ecotoxicological risks to aquatic life, use of these pyrethroids in both terrestrial and freshwater ecosystems must be treated with caution.

Impact of Agricultural Insecticide Vapona on a Freshwater Catfish Heteropneustes Fossilis: A Toxicity Study

This study investigates the critical toxicity of Vapona in the air-breathing freshwater catfish, Heteropneustes fossilis (Bloch). The LC50 values (median lethal concentration) were determined using a static bioassay method over 24, 48, 72, and 96-hour exposure periods. The LC50 values for 24, 48, 72, and 96 hours of Vapona were found to be 400, 378, 320, and 275 ppm, respectively. An increased mucus secretion was observed at higher concentrations, suggesting a physiological response to the toxicant. The potential causes of mortality in the fish were also analyzed and discussed.

Sargassum spp. Ethanolic Extract Elicits Toxic Responses and Malformations in Zebrafish (Danio rerio) Embryos.

The amount of Sargassum spp. arriving in the Caribbean Sea has increased steadily in the last few years, producing a profound environmental impact on the ecological dynamics of the coasts of the Yucatan Peninsula. We characterized the toxicological effects of an ethanolic extract of Sargassum spp. on zebrafish (Danio rerio) embryos (ZFEs) in a 96-h static bioassay using T1 (0.01 mg/L), T2 (0.1 mg/L), T3 (1 mg/L), T4 (10 mg/L), T5 (25 mg/L), T6 (50 mg/L), T7 (75 mg/L), T8 (100 mg/L), T9 (200 mg/L), and T10 (400 mg/L). In this extract, we detected 74 compounds by gas chromatography-mass spectrometry (GC-MS), of which hexadecanoic acid methyl ester, and 2-pentanone 4-hydroxy-4-methyl, were the most abundant. In ZFEs, a median lethal concentration of 251 mg/L was estimated. Exposed embryos exhibited extensive morphological changes, including edema in the yolk sac, scoliosis, and loss of pigmentation, as well as malformations of the head, tail, and eyes. By integrating these abnormalities using the Integrated Biological Response (IBRv2) and General Morphological Score (GMS) indices, we were able to determine that ZFEs exposed to 200 mg/L (T9) exhibited the most pronounced biological response in comparison with the other groups. In the comparative transcriptomic analysis, 66 genes were upregulated, and 246 genes were downregulated in the group exposed to 200 mg/L compared with the control group. In the upregulated genes, we identified several gene ontology-enriched terms, such as response to xenobiotic stimuli, cellular response to chemical stimulus, transcriptional regulation, pigment metabolic process, erythrocyte differentiation and embryonic hemopoiesis, extracellular matrix organization, and chondrocyte differentiation involved in endochondral bone morphogenesis, among others. In the down-regulated genes, we found many genes associated with nervous system processes, sensory and visual perception, response to abiotic stimulus, and the nucleoside phosphate biosynthetic process. The probable connections among the morphological changes observed in the transcriptome are thoroughly discussed. Our findings suggest that Sargassum spp. exposure can induce a wide negative impact on zebrafish embryos. Environ Toxicol Chem 2024;43:1075-1089. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Growth performance and condition factor of <i>Oreochromis niloticus</i> (Linneaus, 1758) after exposure to chemically dispersed Bonny Light crude oil

Dispersants are employed in oil spill situations to emulsify the oil into the water column thereby, facilitating weathering; this is without consideration for aquatic life and productivity. A renewal static bioassay was used to assess the recovery of Oreochromis niloticus after exposure to water accommodated fraction of dispersed Bonny Light crude oil (WAFDCO) and water accommodated fraction of Bonny Light crude oil (WAFCO) at sub-lethal concentrations of 0.2, 0.4, 0.8 and 1.6ml/l, based on the growth performance and condition factor after 49-days exposure and 54-days grow-out phases. The results showed that, the physicochemical parameters of the test media were affected by the concentrations of WAFDCO and WAFCO. The mean weight gain of O. niloticus increased with time in the exposure regimes/concentrations. Growth performance was concentration dependent, the highest mean weight of fish (15.67±0.78g) was from 1.6ml/l concentration of the WAFCO, which was higher than the control. The mean relative growth rate was higher (10.40±0.69%) in the fish from WAFCO while the highest mean specific growth rate (0.85±0.05%) was from WAFDCO. The highest value (3.42) of condition factor (K), was obtained in the 1.6ml/l of the WAFDCO. The K values of the fish from the WAFDCO were slightly higher than those from the WAFCO, which were lower than the control. Condition factor was greater than three which implied that, the fish were in good state, thus, their recovery was good after removal from the contaminated environment; hence, all mitigative actions should be prompt during and after oil spills.

Assessment of genotoxicity in Clarias gariepinus exposed to lethal and sub-lethal concentrations of oilfield chemicals: DNA concentration, purity, and genetic implications

This study investigates the concentration and purity of DNA extracted from Clarias gariepinus after exposure to lethal concentrations (250 ml/l, 200 ml/l, 150 ml/l, 100 ml/l, 50 ml/l, 25 ml/l and 0.0 ml/l for the control) of Xylene: Diesel (X:D) and Oilfield-Based Emulsifiers (O-BE) over 96 hours using static bioassays and sub-lethal concentrations 0 ml/l (control), 12.8 ml/l, 25.6 ml/l, 38.4 ml/l, 51.2 ml/l and 64.0 ml/l) using renewal bioassay for 28 days. 210 juveniles were used for the experiment. The study used PCR and other methods to analyse DNA concentrations and purity in the fish samples. The results indicated variations in DNA concentration, purity, and the presence of micronuclei, suggesting genetic and cytogenetic responses to chemical exposures. The highest DNA concentration was recorded in the 25 ml/l group for both O-BE and X:D, while the lowest was in the 100 ml/l group. The genetic effects of Xylene: Diesel on the molecular level were also examined, with significant gaps in the alignments of experimental groups indicating notable differences in the sequences compared to the control group without chemical exposure. Through detailed analyses, including gel electrophoresis and sequence alignment, the study explores genetic variations and micronuclei frequencies in blood cells, shedding light on the ecotoxicological impacts and potential evolutionary implications of these oil-based substances on African catfish. Understanding the genetic variations induced by lethal concentrations of O-BE in Clarias gariepinus is crucial for assessing the broader environmental impact, as genetic changes in aquatic organisms can affect population health, adaptation, and ecosystem dynamics.

Assessment of Piscicidal Potentials of Carica papaya (Linnaeus, 1753) Leaves, Seeds, and Peel Powder on Juveniles of Clarias gariepinus (Burchell, 1822)

In aquaculture, piscicides are used as fishing gear to combat parasitic, invasive fish species and eliminate dominant fish species in a water body. Therefore, assessment of piscicide activity is important. Hence, in this study, we have aimed to assess the piscicidal potential of Carica papaya leaves, seeds, and peel powder on juveniles of Clarias gariepinus using behavioural responses and mortality rate as the toxicity endpoints. Four hundred and fifty (450) juveniles of Clarias gariepinus were used for the 96-hour static bioassay. Five (5) different concentrations of 0 mgL-1, 25 mgL-1, 50 mgL-1, 75 mgL-1, and 100 mgL-1 containing ten (10) fish samples in triplicates were used. The physicochemical parameters of the test concentrations monitored during the exposure include Temperature, pH, Electrical Conductivity, Dissolved Oxygen, and Total Dissolved Solids. The results of the physicochemical parameters did not vary significantly compared with the control. The results of the behavioural responses showed a range of reactions, such as erratic swimming, gulping of air, loss of reflex, vertical orientation, loss of buoyancy, jumping, and discolouration. The fish mortality rate was used to determine the median lethal concentrations (LC50) of the leaves, seeds, and peel powder using the Probit method. The LC50 values estimated from Probit analysis were 147.17 mgL-1, 262.376 mgL-1, and 697.180 mgL-1, respectively. The results implied that of the three plant parts used, the leaves powder of Carica papaya showed the most promising piscicidal potential. Hence, this underscores screening whole plant parts to ascertain the most suitable for such desired activity. The substitutes of plant substances, which can act as ecologically friendly piscicides, can be encouraged against commonly used synthetic chemicals which can be detrimental to aquatic ecosystems.

Lethal Toxicity of Aqueous Extract of Sodom Apple (Calotropis procera) on African Catfish (Clarias gariepinus) (Burchell, 1822) Juveniles

The experiment was performed to check the lethal toxicity of aqueous extract of Calotropis procera on Clarias gariepinus juveniles. A range finding test was done and the concentrations for the definitive tests were determined. A total of 150 African catfish juveniles of average weight 9.37±0.08g were randomly selected and distributed into four treatments in triplicates of 20mg/L, 40mg/l, 60mg/L, 80mg/L concentrations and a control (0.00) using a static bioassay test over a period of 96 hours. Behavioral responses observed during exposure of the fish to lethal concentrations included erratic swimming, air gulping, haemorrhage, loss of equilibrium and sudden death. All data obtained were summarised using descriptive statistics for the mortality, water quality parameters, growth performance and nutrient utilization. While one-way analysis of variance (ANOVA) was used to assess differences in means among the concentrations and Duncan multiple range tests was used to separate the means, where there was a difference. Physico-chemical water parameters and haematological parameters showed various significant difference among the treatments (P< 0.05). C. procera at higher concentrations of 40mg/L and above was highly toxic to fish, which led to erratic behavior and mortality.

Effect of Carica papaya (paw-paw) aqueous leaf extract on the growth, haematological parameters and the liver enzymes of Clarias gariepinus juveniles

It is common practice to use herbs to supplement for fish feed and as a way to trap fish during fishing expeditions. The use of these plant materials causes more harm than good in aquaculture species because of lack of knowledge of the side effects. The study was to find acute toxicity of the lethal dose (LD50) of Carica papaya leaf extract on Clarias gariepinus juveniles, hematological parameters, weight changes, liver enzymes. A total number of 200 C. gariepinus juveniles were used for the study. Juveniles were grouped into 5 groups for acute toxicity with different extract concentrations; 290.95 mg/l, 529.00 mg/l, 767.05 mg/l, 1005.10 mg/l, and 1243.15 mg/l. Based on the result of acute toxicity tests, assessment of sub-acute toxicity test was made, using different extract concentration; 290.00 mg/l, 502.50 mg/l, 714.15 mg/l and 925.75 mg/l. Administration of extract lasted for 28 days behavioural changes were observed in the experimental animals at the 96 h static bioassay. Weight were observed, specific growth rate was the lowest in 925.75 mg/l and the control. Hematological assay showed changes in the packed cell volume (PCV), red blood cell count (RBC), haemoglobin concentration (Hb), mean corpuscular volume (MCV), and mean corpuscular haemoglobin (MCH) as they were significantly increased in comparison to the control. Mean corpuscular haemoglobin concentration (MCHC) showed no response except on day 7 when it declined significantly in fish exposed to 290.0 mg/l of extract. The white blood cell differentials and liver enzymes-alanine aminotransferase activity (ALT), aspartate aminotransferase activity (AST) and alkaline phosphatase (ALP) were unaffected. The increase in red blood cell may be indicative that leaf extract of Carica papaya may have anti-anaemic properties. The absence of changes in the white blood cell and liver function enzymes, may be indicative that C. papaya leaf extract has no toxic effect on the juveniles.

Bioremediation Potential of Duckweed (Lemna paucicostata) on Wastewater from a Mechanic Workshop, Port Harcourt, Nigeria

Wastewater pollution and its bioremediation remain a major challenge in urban areas. Lemna paucicostata were exposed to wastewater containing some amount of used engine oil in a four-week relative static bioassay. The physicochemical characteristics of the wastewater were determined using standard methods. The results obtained from the experiment showed that L. paucicostata was able to purify and concentrate nutrients from the wastewater. The efficacy of purification was manifested in the results where the total hydrocarbon content reduced from 8.15% - 4.00% over the period. Turbidity also reduced from 66.7% - 23.08%; biochemical oxygen demand reduced from 70.00% - 14.29%. Phosphate and nitrate also reduced from 34.59% - 12.09% and 39.74% - 11.92%, respectively. Chemical oxygen demand and total suspended solids increased from 22.92% - 73.16% and 2.90% - 14.39% respectively, over the periods. The temperature slightly changed from 29.3oC to 29.5oC. The pH also changed slightly from 7.00 – 7.50, making the wastewater slightly alkaline. Slightly alkaline conditions enhance overall hydrocarbon biodegradation in wastewater. However, prolonged exposure of L. paucicostata led to its mortality especially in the higher concentrations of hydrocarbons. Percentage mortality increased with concentrations and period of exposure, from 10% to 60% at the 3rd week and from 20% to 80% at the 4th week. Lethal concentration (LC50) of 14.60ppm was noticed at the 3rd week, while LC50 of 12.60ppm was noticed at the 4th week. The effectiveness of this algae, L. paucicostata, on the bioremediation of wastewater is not only of scientific but also of economic and social importance.

Toxicity of crude extract of <i>Terminalia superba</i> sawdust to <i>Clarias gariepinus<i/> (Burchell 1822)

The study examined the toxicity of Afara tree (Terminalia superba) sawdust extract to African catfish, Clarias gariepinus. The fish were exposed to four concentrations 55 ml/L, 60 ml/L, 65 ml/L, 70 ml/L and the control for 96 hours. C. gariepinus juveniles exposed to sublethal concentrations of T. superba extract were examined in a static bioassay with reference to behavioural, haematological and histopathological changes. Early observations of fish exposed to T. superba extract showed erratic swimming, loss of equilibrium and respiratory distress. The behavioural response was dose-dependent and decreased with a decrease in concentration. At 24-96 hours of exposure, there were no significant differences in the temperature and pH (p>0.05) while there was a significant difference (p<0.05) in dissolved oxygen at 48-96 hours. The haematological results showed varying degrees of effects of the extracts on blood parameters. The histopathological changes of the gills of fish exposed to T. superba at 65-70 ml/L showed gills distortion, epithelial hyperplasia and disruption of primary lamellar epithelium and that of gills of fish in the control revealed a normal gill filament. Also, the liver of C. gariepinus of the control fish revealed normal structures. Histology of the liver of C. gariepinus in 65 ml/L and 70 ml/L showed varying degrees of space formation, vacuoles in the tissue and increased haemorrhage. The LC50 value of 53.35 ml/L was gotten. It was therefore concluded that sawmill wood waste did not only impact the water quality but also negatively affected the proper functioning of the gills and liver of C. gariepinus.

Toxicological effects of meloxicam on physiological and antioxidant status of common carp (Cyprinus carpio).

Fish in aquatic environments are end consumers of the food chain and are widely used for the evolution effects of environmental pollution and their interactions in aquatic ecosystem. In the present study, common carp (Cyprinus carpio) fingerlings were selected to assess the potential risk and aquatic toxicity of meloxicam as a non-steroidal anti-inflammatory and a commonly used pharmaceutical drug. In order to evaluate meloxicam toxicological effect on haematological, antioxidant status, enzymological and histological parameters, based on its LC50 24h acute toxicity (10.05mgL-1 ), fish fingerlings were exposed to four doses of meloxicam including; 0 (control), 0.1 (low), 1 (medium) and 2mgL-1 (high) under static bioassay method for 28 days. The results showed that sublethal doses of meloxicam significantly decreased alanine aminotransferase, alkaline phosphatase, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) levels in comparison with the control group after 28 days (p<0.05). However, red blood cell, haematocrit, haemoglobin and malondialdehyde values in fish exposed to meloxicam significantly increased alongside its concentration (p<0.05) more than the control group after 28 days. SOD, CAT and GPX mRNA expression levels in gill, liver, kidney and brain organ of fish under meloxicam treatment were significantly down-regulated compared to the control group (p<0.05). Histopathological assessment showed the increased vacuolation in hepatocytes in liver of fish exposure to medium and high doses of meloxicam. In conclusion, meloxicam induces oxidative stress in common carp which results a disruption of physiological and health status of this species based on our current findings.

Behavior Changes and LC50 of Dried Garlic (Allium sativum) Acute Toxicity in Nile Tilapia (Oreochromis niloticus) Juvenile [RESEARCH NOTE

Plant-based compounds are emerging substitutes for chemical treatments in aquaculture since they are known to cause less harm to both the environment and its organisms. Garlic (Allium sativum) is a popular herb that has a broad range of uses, especially in the control and treatment of bacterial and parasitic diseases. However, its toxicity to tilapia is not well-studied. Hence, this study was conducted to test the toxicity levels of garlic powder in juvenile Nile tilapia (Oreochromis niloticus) by determining the cumulative mortality and median lethal concentration (LC50). Test fish were exposed through immersion in 6 concentrations (150, 200, 250, 300, 350, and 400 mg L-1) of garlic powder with 25% allicin and a control in 96 h static bioassay. Within 24 h, test fish exposed to 250 mg L-1 garlic and above, exhibited abnormal behaviors such as lethargy, gasping for air, and weak responses to environmental stimuli. Cumulative mortality was highest at 100% in 400 mg L-1 garlic at 48 h. Mortalities were dependent on the concentration and duration of exposure. The 96 h LC50 of garlic powder to O. niloticus was 225.86 mg L-1 with lower and upper confidence limits of 210.37 and 242.50 mg L-1, respectively at 27°C.

Histological and hematological changes to Clarias gariepinus juveniles exposed to acute doses of Emamectin benzoate in a static bioassay.

Emamectin benzoate (EMB) is a potent neurotoxic pesticide, extensively used in agriculture and aquaculture in Nigeria. The knowledge of its toxicological impact to C. gariepinus in Nigeria is scarce. Thus, the investigation was designed to uncover its 96 h LC50, safe level to aquatic media, histological impact on fish liver, gill and hematological changes in the blood parameters. 96 h LC50 was 0.34 mg L-1. Safe level of EMB was 0.034 mg L-1. Dose dependent liver degenerations were characterized by; Congestion of the central vein by inflammatory cells, pyknotic nuclei of hepatocytes, coagulation necrosis, focal necrosis, dilations of sinusoidal spaces and infiltration of periportal regions by inflammatory cells. Dose dependent changes in gill were characterized by; mucus secretion, shrinkage of secondary lamellae, hyperplasia, occlusion of secondary lamellae, degeneration of gill cartilage, necrosis of respiratory epithelia and erosion of secondary lamellae. Red blood cell indices decreased minimally at the end of the 96 h exposure. White blood cell count (WBCC), mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) were significantly (p ≤ 0.05) elevated in three treatments. Neutrophils decreased significantly (p ≤ 0.05), basophils, eosinophils and monocytes showed mixed tendencies. The findings of this investigation imply that C. garipinus exposed to EMB may cause dose and time-dependent changes in the liver and gill histology as well as alterations in the fish's hematological profile, all of which were harmful to the fish's health. To avoid negative effects on fish in nearby aquatic settings, it is advised that the use of EMB be monitored and limited.

A New Bioassay for the Detection of Paralytic and Amnesic Biotoxins Based on Motor Behavior Impairments of Zebrafish Larvae.

The global concern about the increase of harmful algal bloom events and the possible impacts on food safety and aquatic ecosystems presents the necessity for the development of more accessible techniques for biotoxin detection for screening purposes. Considering the numerous advantages that zebrafish present as a biological model and particularly as a toxicants sentinel, we designed a sensitive and accessible test to determine the activity of paralytic and amnesic biotoxins using zebrafish larvae immersion. The ZebraBioTox bioassay is based on the automated recording of larval locomotor activity using an IR microbeam locomotion detector, and manual assessment of four complementary responses under a simple stereoscope: survival, periocular edema, body balance, and touch response. This 24 h acute static bioassay was set up in 96-well microplates using 5 dpf zebrafish larvae. For paralytic toxins, a significant decrease in locomotor activity and touch response of the larvae was detected, allowing a detection threshold of 0.1-0.2 µg/mL STXeq. In the case of the amnesic toxin the effect was reversed, detecting hyperactivity with a detection threshold of 10 µg/mL domoic acid. We propose that this assay might be used as a complementary tool for environmental safety monitoring.

Assessment of piscicidal effect of five toxicants for the eradication of weed fish Nile tilapia (Oreochromis niloticus)

Unwanted or weed fish in aquaculture pond may affect the growth and development of cultured fish species. The current investigation aimed to assess the piscicidal effect of five commercial toxicants on weed fish, Nile tilapia (Oreochromis niloticus) for a short period. The fish was exposed to four concentrations (0.5, 1.0, 1.5, and 2.0 ppm) of dimethoate, pyrethroid lambda-cyhalothrin, cypermethrin, malathion, and Chillas along with control (without any toxicants) during a 48-hour static bioassay. Fish mortality and physicochemical parameters i.e., pH and dissolved oxygen (DO) of water were checked after every 8 hours. The pH of water varied from 3.46to 6.5 and DO range 2.70-5.66 during all experiments. After 48 hours of exposure, the maximum fish mortality was achieved by dimethoate (4.15, 8.30%), cypermethrin (4.16, 8.32%), malathion (4.0, 8.00%), and Chillas (4.0, 8.00%) at the highest applied concentration (2.0 ppm). While pyrethroid lambda-cyhalothrin showed the highest mortality at 1.5 ppm (4.16) with 8.32% as well as on 2.0 ppm (4.16, 8.32%). In conclusion, pyrethroid lambda-cyhalothrin was observed as the best toxicant as piscicide causing overall higher mortality on all applied concentrations. However, the long-term experiment is further needed to clarify the mortality trend and optimization of toxicants in a long-term experiment.