Opercular Beat Research Articles

Behavioral, electrocardiographic, and opercular beat recording characterization of tilapia (Oreochromis niloticus) in immersion bath with different concentrations of tricaine (MS-222)

In the world scenario of farmed fish production, tilapia stands out as one of the most cultivated species. In view of animal welfare in fish farming, stressful practices such as biometrics and transportation are minimized by the use of anesthetic agents, with tricaine (MS-222) being among the most commonly used. Despite its extensive use, its anesthetic responses remain a focus of investigation for animal safety. Therefore, the present study aims to evaluate the electrocardiographic and respiratory activity of juvenile Nile tilapia exposed to different concentrations of tricaine. In this study, juvenile Nile tilapia (30.9 ± 5.5 g, n = 99) were subjected to tricaine anesthetic baths at concentrations of 150–250 ppm for behavioral analysis and electrophysiological recordings (electrocardiogram and opercular beating). Our results show that induction and recovery of anesthesia with tricaine in juvenile Nile tilapia was effective for a short-term anesthesia with dose-dependence characteristics. Furthermore, the electrophysiological data reveal a marked decrease in heart rate (28.10–44.08 %) and opercular beating (35.72–59.19 %), depending on the concentration of tricaine used, with reversibility during the recovery period. Therefore, we can infer that the safe utilization window for tricaine varies between 150–250 ppm in juvenile tilapia, emphasizing that its administration should consider the anesthetic plan with monitoring of physiological parameters, especially respiratory ones, which are more easily evidenced.

Fin clipping does not increase opercular beat rate in tricaine-treated zebrafish.

To carry out research with genetically modified animals, their genotype has to be assessed. A standard protocol to obtain required tissue samples from zebrafish is finclipping. However, some studies reported considerable stress induced by this protocol. We therefore assessed ventilation as a read-out for stress in zebrafish that underwent finclipping during routine genotyping in our fish facility. Our analysis could not confirm a strong increase of ventilation as had been previously reported. Instead, handled zebrafish showed ventilation rates in the range of controls that remained in their holding tanks. Additionally, we detected a slight reduction of ventilation rates up to an hour after anaesthesia in zebrafish treated with tricaine only, suggesting a prolonged protecting effect by this anaesthetic.

Behavioral and electrophysiological study in Colossoma macropomum treated with different concentrations of Nepeta cataria oil in an immersion bath revealed a therapeutic window for anesthesia.

The purpose of this study was to characterize the activity of essential oils from Nepeta Cataria (EON) at concentrations of 125 L-1, 150 L-1, 175 L-1, and 200 L-1 on the behavior of loss of the posture reflex and recovery of the posture reflex and electrocardiographic activity and recording of the opercular beat of Colossoma macropomum during immersion bathing for a period of 5min, in order to obtain a window for safe use during anesthesia. The fish (23.38 ± 3.5g) were assigned to the following experiments: experiment 1 (latency to loss and recovery of the posture reflex): (a) 125 L-1, (b) 150 L-1, (c) 175 L-1, and (d) 200 L-1 (n = 9) per group. Experiment 2 (electrocardiographic and heartbeat recordings): (a) control group; (b) vehicle control group (2ml of alcohol per liter of water), (c) 125 L-1, (d) 150 L-1, (e) 175 L-1, and (f) 200 L-1 (n = 9), per group. All the concentrations used showed efficacy in inducing loss of the posture reflex and reversibility with recovery of the posture reflex, but the electrocardiographic recordings indicated morphographic changes such as bradycardia during induction and p wave apiculation during recovery at the highest concentrations tested. In this way, we suggest a safe use window for short-term anesthesia with EON in the concentration range of 125 to 150 L-1 for juvenile Colossoma macropomum.

Effective concentration of herbal anaesthetics Origanum vulgare L. oil and its effects on stress parameters in Nile tilapia (Oreochromis niloticus).

Using anaesthetics is an important application in aquaculture especially where the fish transportation, vaccination, grading, sorting activities and many other handling operations have been conducted during the different stages of production periods in the farms or hatcheries. This study aimed to evaluate the efficacy of oregano essential oil (OO) as an anaesthetic for Nile tilapia and to determine the optimal concentration and post-application stress effects compared to clove oil (CO). Nile tilapia juveniles were exposed to different concentrations of OO (20-40-60-80-100mgL-1) and CO (50mgL-1) for different time periods to determine the optimal concentration and exposure time. After the effective concentration of OO was determined, in the second experiment, stress parameters (glucose, plasma cortisol) were analysed after 0, 2, 6, 12 and 24h of application. The results compared to the control group and CO results. The study found that OO which has carvacrol compound higher than 78% was an efficient anaesthetic for Nile tilapia, and the effective concentration was found to be 60mgL-1. No significant differences were found between opercular beats in any concentration of OO and CO. Basal glucose level in blood without anaesthesia application and recorded at 39.33mgdL-1 and significantly lower than OO and CO at first two sampling points, 0 and 2h (p<0.05). According to plasma cortisol level results, although CO experimental group showed secondary stress response at 12h (17.91±4.21ngmL-1), OO and CO group cortisol levels decreased at 24h after anaesthesia application 7.13±0.14and 7.01±0.54ngmL-1, respectively, below the control group cortisol concentration (12.28±1.81ngmL-1). These findings have important implications for the aquaculture industry as the use of OO as an anaesthetic could reduce the stress and mortality associated with traditional anaesthetics. Further research is needed to evaluate the efficacy of OO as an anaesthetic agent for other fish species and to determine the optimal concentration and exposure time for different species.

Ecotoxicity of commonly used oilfield-based emulsifiers on Guinean Tilapia (Tilapia guineensis) using histopathology and behavioral alterations as protocol.

This study examined the histological aberrations in the gill and liver tissues and behavioural changes of Tilapia guineensis fingerlings exposed to lethal concentrations of used Oilfield-based emulsifiers for 96 h. Various concentrations of the surfactants were tested, ranging from 0.0 to 15.0 ml/L. The behaviour of the fish was observed throughout the experiment, and the results showed that increasing concentrations of the surfactants led to progressively abnormal behaviour, including hyperventilation and altered opercular beat frequency. These behavioural changes indicated respiratory distress and neurotoxic effects. Histological analysis revealed structural aberrations in the gill and liver tissues, with higher concentrations causing more severe damage, such as lesions, necrosis, inflammation, and cellular degeneration. This implies that surfactants released even at low concentrations are capable of inducing changes in the tissues of aquatic organisms. These findings highlight the toxic effects of the surfactants on fish health and provide biomarkers of toxicity. Future research should focus on understanding the specific mechanisms and long-term consequences of surfactant toxicity on fish genetic composition, populations, and ecosystems to implement effective conservation measures.

Noninvasive health monitoring of fish using optical ventilation signals

Fish health monitoring systems in land-based aquaculture must be noninvasive, with no sensors on the surface or inside the fish, in order to minimize stress. This study developed a method for monitoring optical ventilation signals from the operculum movement of olive flounders (Paralichthys olivaceus) and combined it with decision trees, a type of machine learning, to achieve continuous and long-term monitoring. The optical ventilation signal monitoring system was realized using a tank with an interpolated multichannel optical detection probe. The proposed system acquires channel signals using a four-channel optical detection probe situated around the gills of the flounder and processes the channel signals every 10 s in mini-batches to classify and select the optical ventilation signal that best reflects the operculum movement, thereby improving robustness. The opercular beats, which represent ventilation frequency, were calculated from the optical ventilation signal to enable continuous monitoring. To further demonstrate the usefulness of this system, the stress response to high water temperature exposure was monitored and compared to the opercular beats and the variability in plasma glucose concentration, which is used as a stress indicator in fish. The results suggest that the opercular beats respond sensitively to stress application, and the system is useful for fish health monitoring.

Light-specific wavelengths differentially affect the exploration rate, opercular beat, skin color change, opsin transcripts, and the oxi-redox system of the longsnout seahorse Hippocampus reidi

Light is a strong stimulus for the sensory and endocrine systems. The opsins constitute a large family of proteins that can respond to specific light wavelengths. Hippocampus reidi is a near-threatened seahorse that has a diverse color pattern and sexual dimorphism. Over the years, H. reidi's unique characteristics, coupled with its high demand and over-exploitation for the aquarium trade, have raised concerns about its conservation, primarily due to their significant impact on wild populations. Here, we characterized chromatophore types in juvenile and adult H. reidi in captivity, and the effects of specific light wavelengths with the same irradiance (1.20 mW/cm2) on color change, growth, and survival rate. The xanthophores and melanophores were the major components of H. reidi pigmentation with differences in density and distribution between life stages and sexes. In the eye and skin of juveniles, the yellow (585 nm) wavelength induced a substantial increase in melanin levels compared to the individuals kept under white light (WL), blue (442 nm), or red (650 nm) wavelengths. In addition, blue and yellow wavelengths led to a higher juvenile mortality rate in comparison to the other treatments. Adult seahorses showed a rhythmic color change over 24 h, the highest reflectance values were obtained in the light phase, representing a daytime skin lightening for individuals under WL, blue and yellow wavelength, with changes in the acrophase. The yellow wavelength was more effective on juvenile seahorse pigmentation, while the blue wavelength exerted a stronger effect on the regulation of adult physiological color change. Dramatic changes in the opsin mRNA levels were life stage-dependent, which may infer ontogenetic opsin functions throughout seahorses' development. Exposure to specific wavelengths differentially affected the opsins mRNA levels in the skin and eyes of juveniles. In the juveniles, skin transcripts of visual (rh1, rh2, and lws) and non-visual opsins (opn3 and opn4x) were higher in individuals under yellow light. While in the juvenile's eyes, only rh1 and rh2 had increased transcripts influenced by yellow light; the lws and opn3 mRNA levels were higher in juveniles' eyes under WL. Prolonged exposure to yellow wavelength stimulates a robust increase in the antioxidant enzymes sod1 and sod2 mRNA levels. Our findings indicate that changes in the visible light spectrum alter physiological processes at different stages of life in H. reidi and may serve as the basis for a broader discussion about the implications of artificial light for aquatic species in captivity.

Anesthetic effect and acute toxicity of Citrus sinensis essential oil in betta

This study investigated the use of Citrus sinensis essential oil (EOCS) in Betta splendens, evaluating toxicity, induction and recovery times to anesthesia, its action on agonist behavior, and on male collective transport. To toxicity, fish were exposed to EOCS at different concentrations during 48 h. The induction test was performed to evaluate sedation, anesthesia, and recovery under different concentrations. To assess agonist behavior, male subjects were maintained with different dosages of EOCS, assessing opercular beat and fin expansion, while exposed to untreated animals. In the mass transport study, males were divided into two treatments with two levels of EOCS, for 6 h, also analyzing gill histometry at the end of transport. The results obtained show that the mean lethal concentration in 48 h of exposure to EOCS was calculated at 49.17 μL·L−1. The shortest anesthesia induction time was at 300 μL·L−1 EOCS. EOCS was able to reduce agonist behavior in males individual. Histometric analyzes revealed a reduction in the height of gill filaments in fish transported with 20 μL·L-1 EOCS. EOCS can be used as a sedative and anesthetic agent for B. splendens.

African jewel fish (Hemichromis bimaculatus) distinguish individual faces based on their unique iridophore patterns

Previous research has shown that African jewel fish (Hemichromis bimaculatus) recognize pair-bonded mates during their exchanges of egg-guarding duties. The current research examined the perceptual cues for face recognition by comparing two face models displaying anatomically realistic arrangements of blue iridophores derived from discriminant function analysis of distinct sibling groups. Four groups each consisting of 9 subadults were examined using a narrow compartment restraining lateral movement where face models were presented at eye level for eight trials. Because respiratory movement of the operculum can mechanically displace the eye thereby shifting the retinal image, jewel fish reduce their respiration rate during increased attention. When two experimental groups were presented with the same face models on four trials following initial model presentations, both groups exhibited stable respiration rates indicative of model habituation. When the habituated face models were switched to novel face models on the fifth trial, the rates of respiration decreased as measured by reliable increases in the elapsed times of opercular beats. Switching the models back to the habituated models on the sixth trial caused reliable decreases in the elapsed times of opercular beats, resembling the earlier trials for the habituated models. Switching the face models again to the formerly novel models on the seventh trial produced respiration rates that resembled those of the habituated models. The two control groups viewing the same models for all eight trials exhibited no substantial change in respiration rates. Together, these findings indicate that jewel fish can learn to recognize novel faces displaying unique arrangements of iridorphores after one trial of exposure.

Impact of Household Chemicals on the Ornamental Fish Poecilia sphenops (Valenciennes)

This study examined the impact of various household chemicals, such as Surf excel, hair dye, popular soap, fabric softener, shampoo, and coconut oil, on the ornamental fish Poecilia sphenops (Valenciennes in Cuvier and Valenciennes, 1846). Length-weight relationships, gonadosomatic and hepatosomatic indexes, oxygen consumption, and opercular beat rate were measured to assess the effects of the chemicals (10, 20, and 30 ppm) on the fish. Results showed that at higher concentrations of the chemicals, the fish exhibited increased breathing and signs of distress. The temperature of 28°C was found to be optimum for the growth of P. sphenops, while the lowest growth performance was shown at temperature 30°C. Fish ranged from 37 to 67 mm in total length and 1.10 to 3.10 g in body weight. The female to male sex ratio (4.9:1) deviated significantly from the unity (?²= 214.2, p&lt;0.05). These findings indicate that the presence of such noxious chemicals are deleterious to natural populations of fish, and that the irresponsible discharge of sewage water into water bodies should be avoided.

Hydrogen peroxide in seahorse aquaculture: Determining safe exposure levels using non-invasive biomarkers of stress

Hydrogen peroxide (H2O2) is widely used in aquaculture to prevent and control fish mortality often associated with fungal, bacterial, and parasitic infections. Its main advantage by its reduced environmental impact. However, H2O2 affects redox regulation of cell survival and proliferation, controls inflammatory and immune responses, and is related to oxidative stress. Here we evaluated the behavioral response, opercular beats, and weight loss as stress indicators in captive-bred Hippocampus reidi seahorses exposed to four different concentrations of H2O2 (4.4 mM, 10.9 mM, 12.0 mM, and 13.0 mM). The lowest concentration (4.4 mM) was considered safe up to 60 min of exposure, with little impact on weight loss, behavior changes, and opercular beats. Conversely, H2O2 concentrations ≥10.9 mM led to a high frequency of stress-associated behaviors (irregular swimming, pipe, and curled tail), severe alterations in locomotion and opercular beats, and were lethal at 12 mM and 13 mM. The lowest dose tested increased the locomotion time of seahorses by 55% and decreased benthic behavior by 47% compared to seahorses not exposed to H2O2. The opercular beats were increased in the presence of H2O2 following a dose-response curve. H2O2 exposure induced a significant decrease in the mean body weight of the seahorses in a dose-dependent manner. We conclude that H2O2 can be used as a potential treatment by immersion (i.e. bath) for H. reidi in a concentration of 4.4 mM for 60 min.

Integrated behavioural, neurological, muscular and cardiorespiratory response in tambaqui, Colossoma macropomum anaesthetized with menthol

Menthol has been recommended for fish anaesthesia in recent studies. However, no observations of brain electrical activity, electromyography and electrocardiogram have been reported to date in in vivo experiments using menthol. In order to fill the gaps at the electrophysiological and behavioural levels, juveniles of tambaqui, Colossoma macropomum were used as live models and subjected to two experimental conditions: I - Behavioural assessment using menthol at 100 mg.L−1; II - Characterization of electroencephalography (EEG), electromyography (EMG), electrocardiography (ECG), and opercular beat rate (OBR) using menthol at 100 mg.L−1. The fish were assayed into three groups for all characterizations: (a) control; (b) ethanol (vehicle control); and (c) menthol at100 mg.L−1, nine animals per group were used for each marker, one fish being considered a replicate (n = 9) and used only once. On the EEG, it was observed that menthol induced decreased mean power in cerebral activity, indicating the deepening of the anaesthesia, showing that menthol led to reversible CNS depression, with the resumption of mean power after washout, devoid of seizures or any other observable alterations. The EMG showed a decreased skeletal muscle tone, with no excitability or muscle spasms. The ECG showed a reduced heart rate, however, menthol did not elicit important alterations during induction or recovery in the duration of the QRS complex (ventricular depolarization). For all records the sinus rhythm was maintained, menthol did not lead to deleterious QT interval (ventricular contraction) prolongation, and the RR interval (time between two successive QRS complexes) corroborated a reversible anaesthetic effect. OBR showed the maintenance of the ventilatory rate during induction and recovery, which indicates a reduced risk of causing severe hypoxia. Overall, the electrophysiological data reinforced the results observed in the behavioural assessment. The findings indicate that menthol proved to be an effective and safe anaesthetic for tambaqui juveniles, as it did not cause major changes in the pattern of tracings, and therefore, should be considered a standard chemical compound of plant origin for the purpose of full immobilization and general anaesthesia of C. macropomum.

Capacity for thermal adaptation in Nile tilapia (Oreochromis niloticus): Effects on oxygen uptake and ventilation

Standard metabolic rate (SMR) and maximum metabolic rate (MMR) were determined for Nile tilapia acclimated to six different experimental temperatures from 18 °C to 38 °C. SMR increased exponentially with temperature, from 79.8 mg O2 kg−1 h−1 at 18 °C, to 255.1 mg O2 kg−1 h−1 at 38 °C (Q10 = 1.79). The main increase in Q10 occurred within the highest temperature range, whereas in the lower temperature from 18 °C to 22 °C, temperature did not significantly affect SMR. MMR showed a hyperbolic correlation with increasing temperature, rising from 240.5 mg O2 kg−1 h−1 at 18 °C to a peak of 373.8 mg O2 kg−1 h−1 at 30 °C, before decreasing again at higher temperatures. Absolute aerobic scope (AAS) peaked at 26.0 °C, which we conclude to be the optimal temperature for Nile tilapia. The optimal temperature range, defined as the thermal range where 80% or more of the metabolic scope (MS) can be maintained, occurred between 19.5 and 32.1 °C. The lower (TCMIN) and upper (TCMAX) critical temperatures occurred at 13.1 °C and 38.8 °C. Nile tilapia showed a 4-fold scope for increasing ventilation frequency from 24 opercular beats min−1 (OB min−1) during SMR at 18 °C, to a maximum of 100 OB min−1 which occurred during MMR at 34 °C. fV during MMR increased with temperature, but above 30 °C became uncoupled with MO2, as fish were unable to sustain their rates of oxygen consumption despite a high fV. There was a strong correlation between fV and SMR (r2 = 0.83) across all temperatures indicating that fV is a good predictor of SMR. However, the correlation between MMR and fV was weak (r2 = 0.06), due to a strong interacting effect of temperature. When selecting data from the thermal optimum range, a good correlation between fV and MO2 was obtained (r2 = 0.74).

Boldness Predicts Aggressiveness, Metabolism, and Activity in Black Rockfish Sebastes schlegelii

Animal personality refers to individual behavioral and physiological differences that are consistent over time and across context. Recently, the fish personality has gained increasing attention, especially from the perspective of aquaculture production. Here, we used an important aquaculture species, black rockfishSebastes schlegelii, as the target animal, and conducted a series of experiments to explore the relationships among fish boldness, aggressiveness, locomotor activity, opercular beat rate, standard metabolic rate, and cortisol level. Generally, the results showed that the boldness of black rockfish was significantly, positively correlated with fish aggressiveness, stressed locomotor activity, and standard metabolic rate, while was negatively correlated with stressed opercular beat rate. Bold fish had significantly higher aggressiveness, standard metabolic rate, and stressed locomotor activity but lower stressed opercular beat rate. However, there were no significant correlations between boldness and basal locomotor activity or between boldness and basal cortisol level. These results preliminarily constructed the behavioral and physiological spectrum of black rockfish in the context of fish personality and clearly indicated that the boldness could be used as a discrimination tool to predict fish aggressiveness and metabolic rate, which may have valuable applications for decreasing fish harmful aggression and increasing fish welfare in the aquaculture industry.

TOXICITY OF METHANOL EXTRACT OF JATROPHA GOSSYPIFOLIA L. (BELLYACHE) TO THE JUVENILES OF CLARIAS GARIEPINUS, (BURCHEL)

Juveniles of Clarias gariepinus (Burchel) of length 15.75 ± 00.50 cm and weight 14.75 ± 1.25g were exposed to methanol extract of Jatropha gossypifolia L. at concentrations of 0.00, 3.00, 4.00, 5.00, 6.00 and 7.00 mgl-1 in three replications for 96 hours to determine the acute toxicity. Agitated swimming, loss of balance, ventral resting position, and death were observed as symptoms of toxicosis. Opercular ventilation was significantly higher than the control at P<0.05. A dose dependant significant increase P<0.05 of the opercular beats was observed in the first 48 hours, which decreased with time. The lethal concentration at 96 hours (LC50) was 4.90mgl-1. The use of J. gossypifolia as a means of catching fish should be discouraged considering that the non target organisms may also be affected. Key words: Toxicity, Jatropha gossypifolia, Clarias gariepirus.

Screening of Anaesthetics in Adult Zebrafish (Danio rerio) for the Induction of Euthanasia by Overdose.

Simple SummaryAlthough zebrafish are used in vast numbers in laboratories all over the world, no consensus has been reached in the scientific community on a humane, consistent, and effective method for euthanasia of this species. Here, we screened commonly used anaesthetic drugs to see if an overdose could induce loss of reflexes of adult zebrafish in a rapid and reliable manner, and without causing distress. The tested anaesthetics were isoeugenol, clove oil, 2-phenoxyethanol, tricaine, benzocaine, lidocaine hydrochloride, and etomidate. We found that lidocaine hydrochloride, buffered with sodium bicarbonate and ethanol to increase its efficacy, induces loss of reflexes in a fast, predictable, and relatively peaceful manner. We recommend its use for adult zebrafish euthanasia.Zebrafish are often euthanized by overdose of anaesthesia. However, fish may have aversion towards some anaesthetics, and protocol efficacy varies between species. Using wild type adult Danio rerio, we assessed time to loss of opercular beat, righting, and startle reflexes during induction of anaesthetic overdose by either tricaine (0.5 g/L or 1 g/L), benzocaine (1 g/L), 2-phenoxyethanol (3 mL/L), clove oil (0.1%), isoeugenol (540 mg/L), lidocaine hydrochloride (1 g/L), or etomidate (50 mg/L). Initial screening demonstrated that benzocaine and buffered lidocaine hydrochloride achieved the fastest loss of reflexes. The rapid induction times were confirmed when retesting using larger batches of fish. The fastest induction was obtained with 1 g/L lidocaine hydrochloride buffered with 2 g/L NaHCO3, in which all adult zebrafish lost reflexes in less than 2 min. Next, we monitored signs of distress during benzocaine or buffered lidocaine hydrochloride overdose induction. The results indicated that buffered lidocaine hydrochloride caused significantly less aversive behaviors than benzocaine. Finally, we tested several buffers to refine the lidocaine hydrochloride immersion. The most efficient buffer for euthanasia induction using 1g/L lidocaine hydrochloride was 2 g/L NaHCO3 with 50 mL/L 96% ethanol, inducing immobility in less than 10 s and with only 2% of adult zebrafish displaying aversive behaviors during treatment.

BEHAVIOURAL RESPONSES OF AFRICAN CATFISH ( Clarias gariepinus BURCHELL, 1822) JUVENILES EXPOSED TO ACUTE CONCENTRATIONS OF BUTACHLOR (HERBICIDE)

This study examined the behavioral changes induced by butachlor to the juveniles of Clarias gariepinus. The experiment consists of five treatments (0.6, 0.7, 0.8, 0.9 and 1.0 mg/l) and a control. Ten fishes were allotted in each test tank in duplicates. Observations on behavioral responses were made at 0, 12, 24, 48, 72 and 96 hours post-exposure. The opercular movement and tail fin beat rates were observed as counts per minute using a stopwatch. The behavioral patterns of the fish in the control group were normal, whereas in the exposed groups the fish tend to lose equilibrium and swim erratically with vigorous jerky movements. At the 12th and 24th hours the fish in the exposed groups showed hyper-active movement, but became hypoactive at the 48th hour. The mean values of the tail fin beat of the exposed groups were significantly higher (p&lt;0.05) than that of the control at the 12th hour. At the 24th and 48th hour post-exposure the exposed groups showed significant (p&lt;0.05) time-dependent decrease compared to the control. The tail fin beat became significantly higher (P&lt;0.05) in the control group from 72nd hours onward. The decrease of tail fin beats at the 72nd and 96th hours were dose-dependent similar observations were also recorded in the opercular ventilation. At the 12th hour the opercular ventilation of the exposed fish was significantly higher (p&lt;0.05) than the control whereas at the 24th and 48th hours, the opercular ventilation of the exposed groups showed a significant decrease (p&lt;0.05) compared to the control.

Acute toxicity of Jatropha curcas (barbados nut) latex extracts to Oreochromis niloticus juveniles

The effects of the latex extract of Jatropha curcas on mortality rate, opercular ventilation rate and some behavioural responses of Oreochromis niloticus juveniles were investigated under laboratory conditions over a 96 hours exposure period. Juveniles of Oreochromis niloticus (Trewavas) were exposed in plastic aquaria to 0.00mg.l-1 (control), 10mg.l-1, 15mg.l-1, 20mg.l-1, 25mg.l-1 and 30mg.l-1. Their opercular beats per minute, tail fin beats per minute, mortality and probit kill were determined. Symptoms of toxicosis observed include agitated swimming, loss of equilibrium, air gulping, periods of quiescence and death. Within 24 hours the opercular ventilation beats and tail fin beats of the exposed fish were significantly higher than in control fish (p&lt;0.05). At 72 hours and 96 hours the opercular and tailfin beats in the control fish were significantly higher (P&lt;0.05) than the exposed fish. The 96 hours LC50 was determined as 5.23 ml/l. Include significance of this study to conclude abstract.&#x0D; Key words: acute toxicity, Jatropha curcas latex extract, Oreochromis niloticus, haematological parameters.

When cooling is worse than warming: investigations into the thermal tolerance of an endemic reef fish, Boopsoidea inornata

Recent investigations suggest that global warming is likely to alter temperature regimes along the southeastern coastline of South Africa through the increased frequency of upwelling events. Identifying thermal thresholds is fundamental in predicting the response of marine ectotherms to rapidly changing ocean temperatures. The aim of this study was to determine the thermal tolerance of the endemic sparid Boopsoidea inornata. To achieve this, 20 wild fish were captured from near Noordhoek in Gqeberha (Port Elizabeth). The fish were exposed to laboratory-simulated upwelling and heat-plume conditions until sublethal endpoints were identified to estimate the critical lower (CTmin) and critical upper (CTmax) thermal limits, respectively. During the simulated cooling or heating events, the opercular beat (OB) rates were recorded, their sublethal endpoints (loss of equilibrium) were identified, and their CTmin and CTmax were estimated. Breakpoint analyses of the OB rates identified the lower and upper thermal stress limits to occur at an average of 9 °C and 25 °C, respectively. The CTmin was estimated to be 7.8 °C and the CTmax 30 °C. When compared with in situ temperatures, these limits suggest that B. inornata is susceptible to small reductions in the minimum temperature. Given that the frequency and magnitude of upwelling events are expected to increase in response to global warming, this may have significant consequences for this and other sympatric, resident species.

Geraniol and citronellol as alternative and safe phytoconstituents to induce immobilization and facilitate handling of fish

The efficacy of a product as an anaesthetic can be determined through combining behavioural assessment and the evaluation of selected electrophysiological markers, such as the electromyogram (EMG) and electrocardiogram (ECG) for muscle contraction power and cardiac function characterizations, respectively. This study aimed to evaluate the anaesthetic efficacy of geraniol (GRL) and citronellol (CTL) in tambaqui juveniles, Colossoma macropomum, through concentration-response trials, and their effects on behaviour and cardiorespiratory responses. Fish (24.78 ± 2.50 g) were assayed into two experimental groups: I – Behavioural Assessment: In which six concentrations were tested (10; 30; 50; 70; 90; and 110 μL L−1) for each compound. For both isolates the concentration of 10 μL L−1 did not induce any signs of anaesthesia. As for the other concentrations, all fish were anaesthetized and fully recovered according to behaviour evaluation. Concentrations of 70 μL L−1 GRL and 90 μL L−1 CTL were considered the most effective doses as they promoted anaesthesia and allowed for recovery within appropriate time intervals; II – Electrophysiological Characterization: Concentrations of 70 μL L−1 GRL and 90 μL L−1 CTL were used for the recordings of EMG, ECG, opercular beat intensity and rate (OBI and OBR), and heart rate (HR). For both experiments, nine fish per concentration (n = 9) per analysis were used and each animal was considered a replicate. Our results demonstrated that geraniol and citronelol induced full body immobilization, which resulted at least in part, from the myorelaxant properties of these compounds. GRL and CTL at 70 μL L−1 and 90 μL L−1, respectively were sufficient to render fish fully and rapidly immobilized. Both products transiently reduced ventilation during anaesthesia, nevertheless allowing for complete recovery after exposure. Although either isolate significantly decreased heart rates, they did not compromise resumption of normal cardiac function. In general, no mortalities were observed and all animals recovered after exposure. Both products could be considered safe alternatives for fish handling and other aquaculture-related activities that might require fish immobilization.