Tilapia Oreochromis Mossambicus Research Articles

Per-recruit analysis and proposed sustainable harvest strategy for rednose labeo Labeo rosae and Mosambique tilapia Oreochromis mossambicus in Flag Boshielo Dam, Olifants River, South Africa

Inland fisheries development in South Africa has been proposed to improve rural livelihoods and food security. However, inland fisheries are susceptible to collapse through overfishing. Therefore, establishing biological reference points for these fisheries is essential for long-term sustainability. Here, spawner-biomass-per-recruit (SBR) analysis was used to set biological reference points for a gillnet fishery targeting the rednose labeo Labeo rosae and Mozambique tilapia Oreochromis mossambicus at Flag Boshielo Dam on the Oliphants River in Limpopo Province, South Africa. Both species are currently exploited at the impoundment by subsistence fishers that keep their entire catch. The current yields are estimated at 59 and 172 g yr−1 for L. rosae and O. mossambicus, respectively. The per-recruit analysis showed that age-at-first-capture for both species should be 4 years, at minimum lengths of 280 mm TL and 250 mm TL for L. rosae and O. mossambicus, respectively, with fishers using a minimum mesh size of 100 mm to reduce the risk of stock collapse. To maintain a SBR value greater than 25% of a pristine population, the L. rosae yield could be increased to 98 g yr−1, while the O. mossambicus yield could be increased to 176 g yr−1, following implementation of the recommended mesh size and size limits. A per-recruit analysis for O. mossambicus that includes recruitment variability and error to accurately calculate the biological reference points is recommended.

Assessing biological invasion predatory impacts through interaction strengths and morphological trophic profiling

Biological invasions are a major stressor on ecosystems worldwide, but tools to predict their predatory impact remain limited. Here, we quantified invader impacts using two complementary approaches: functional responses (to reveal per capita and multiple predator interaction strengths) and ecomorphology (to reveal trophic profiles and competitive overlap). We compared Mozambique tilapia Oreochromis mossambicus, a native southern African cichlid, and a near-trophically analogous invasive congener, the Nile tilapia Oreochromis niloticus. Both Nile tilapia and Mozambique tilapia exhibited a potentially prey population destabilizing Type II functional response. In both single and multiple predator pairings, invasive Nile tilapia had significantly greater prey consumption rates than native Mozambique tilapia, and thereby a greater predatory impact than its native congeneric. Attack rates were greater for Nile tilapia than Mozambique tilapia, with both species showing more similar handling times and maximum feeding rates. No evidence for multiple predator effects was detected within or between these species, and therefore impacts of both species increased additively in the presence of conspecific or heterospecific competitors. Morphological trait analyses found general differences between these two species, with the invasive Nile tilapia having distinctively larger lower jaw closing force, gill resistance and gill raker length, which facilitated greater feeding capacities over the native species. Trophic profiles predicted using morphological trait differences showed high dietary overlap and served as evidence for potential exploitative competition between the two species. These results reveal superior interaction strengths and ecomorphological trait profiles of an invasive over native species which could influence impact and native species replacement dynamics. Novel applications of functional response and ecomorphology provide complementary insights into predatory and competitive impacts from invasive species, aiding impact prediction across environmental contexts.

The influence of ghrelin agonist ipamorelin acetate on the hypothalamic-pituitary-testicular axis in a cichlid fish, Oreochromis mossambicus

Ghrelin, a peptide found in the brain and gut, is predicted to play a significant role in the control of various physiological systems in fish. The objective of this study was to examine the impact of ipamorelin acetate (IPA), a ghrelin agonist, on the reproductive axis of the tilapia Oreochromis mossambicus. The administration of either 5 or 30 µg of IPA for 21 days led to a significant and dose-dependent rise in food intake concomitant with a significant increase in the numbers of primary spermatocytes, secondary spermatocytes, and early spermatids compared to the control group. There was a significant rise in the number of late spermatids, as well as the areas of the lobule and lumen, in fish treated with 30 µg of IPA, compared to the control group. Moreover, there was no significant difference in the percentage of gonadotropin-releasing hormone (GnRH)-immunoreactive fibres in the hypothalamus and anterior pituitary gland across different groups. However, a significant elevation in the expression of androgen receptor protein was observed in fish treated with 30 µg of IPA. Furthermore, the concentrations of luteinizing hormone (LH) and 11-ketotestosterone (11-KT) in the serum of fish treated with either 5 or 30 µg of IPA were significantly elevated in comparison to the control group. Collectively, these findings suggest that the administration of ghrelin enhances the development of germ cells during the meiosis-I phase and that this effect might be mediated via the stimulation of 11-KT and androgen receptors at the testicular level and LH at the pituitary level in the tilapia.

Consumption of periphyton and bioseston by Mozambique tilapia in aqua dams with three different substrates

Periphyton-based aquaculture can reduce feed input costs. Here we characterised the periphyton and bioseston formation in aqua dams stocked with net, plastic, and stone substrates. The consumption of periphyton and bioseston from the net substrate by Mozambique tilapia Oreochromis mossambicus fingerlings was evaluated. Three experiments were conducted. In the first experiment, net, stone, and plastic were deployed in triplicates in aqua dams. The net substrate registered the highest (7.74 ± 1.45 g m-2, ±SE) periphyton biomass. Network analysis showed connectedness between the substrates. The degree centrality showed that the net substrate had the highest score, indicating that there were more groups of species with similar functions growing on the net substrate. The net substrate was subsequently used in the second experiment to determine the consumption of periphyton and bioseston by tilapia fingerlings in aqua dams. Three treatments were assigned: N100 (fish fed 100% commercial diet); N50 (fish fed 50% commercial diet); and N33 (fish fed 33% commercial diet). Growth performance did not differ significantly among the treatments, although N50 showed a trend for a higher growth. This suggests that periphyton may be capable of nutritionally compensating for the partial withdrawal of commercial feed. A third experiment was conducted in fibreglass tanks to determine the preference of tilapia between periphyton and bioseston. The prominent values showed that tilapia preferred to feed on bioseston. The best growth performance was achieved in a periphyton-based aquaculture system, and deployment of the net substrate is recommended in tilapia ponds.

Reproductive parameters of Oreochromis mossambicus in Laguna de Los Patos, Cumaná, Venezuela.

A total of 381 specimens of the tilapia Oreochromis mossambicus collected monthly from May 2017 to May 2018 in the Laguna de Los Patos, Cumaná, Venezuela, to evaluate reproductive parameters of this non-native species. Significant differences were found in relation to average height and weight between males and females, with the highest values in males. The sex ratio was 1:1.5 (males:females), which deviates significantly from the expected 1:1 ratio. The mean length of sexual maturity (Lm50) was 18.0 cm in females and 20.1 cm in males, reflecting that females mature at smaller sizes than males. The monthly variations of the gonadosomatic index (GSI) and the stages of sexual maturity show two reproductive peaks during the study, in October 2017 and April 2018, coinciding with the rainy and dry seasons in the region respectively. The condition factor (CF) showed significant differences between months, but not between sexes, with an average of 1.87 in females and 1.84 in males. The average absolute fecundity was 921 ± 604.6 eggs per fish, with a relative fecundity of 8.36 ± 3.09 eggs per gram of fish. Differences in oocyte size in mature females confirm that the species can spawn repeatedly over a period, which is considered an important factor for the establishment of tilapia in non-native environments.

From “Sabang to Merauke”, the presence of non-native Oreochromis mossambicus and Oreochromis niloticus (Cichliformes: Cichlidae) in Indonesia

Mozambique Tilapia Oreochromis mossambicus and Nile Tilapia Oreochromis niloticusare two non-native species of cichlids (Cichlidae: Cichliformes) that have established populations in Indonesia. There are many information about the presence of both non-native species in the country, but detailed distribution is filling a gap of information. We compile unpublished and published distribution records of Oreochromis mossambicus and Oreochromis niloticus from various sources, particularly from iNaturalist (citizen science platform) and GBIF (The Global Biodiversity Information Facility, an international network of country and organizational participants that exists to enable free and open access to biodiversity data from all sources and to support biodiversity science, environmental research and evidence based decision-making). The historical records of O. mossambicus and O. niloticus were reviewed and summarized, and put the certain known distribution records into the map. Our study suggest that O. mossambicus and O. niloticus found widely throughout Indonesia, from Sabang (northwesternost: Aceh Province, Sumatra) and Merauke (southeasternmost: South Papua Province, Papua).

Assessment of Antioxidant Status of Oreochromis mossambicus in Fresh and Brackish Water of Thiruvarur District, Tamil Nadu from India

Antioxidant biomarkers have been used to demonstrate the effects of various’ environmental stressors on certain aquatic organisms. The objective of the study is to analyze the antioxidant status of freshwater and brackish fish such as Oleochromis mosambicus in 2022. Antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase, glutathione S transferase (GST) and 、 Glutathione content (GSH) was with gills, and, Livers and muscles of fresh water fish of Oreochromis mosambicus analyzed. The results of the study showed that superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S transferase and glutathione contained in different tissues (gills, gills and various tissues) Antioxidant enzymes such as glutathione content have been demonstrated and the liver and muscles have been reduced in Oreochromis mossambicus. The decreased activities of these enzymes may be due to contaminant exposure. This modulation in enzyme activity could be due to the mechanism by which Tilapia Oreochromis mossambicus circumvents the salinity stress caused by contaminants. The research will provide more detailed information on the response of antioxidant defenses to tilapia species in dark water environments and the mechanisms of regulation of this response. This future research will undoubtedly benefit some aspects of aquaculture and aquaculture production as well.

Chronic Starvation-Induced Alterations in Biochemical Parameters and Hypothalamic-Pituitary-Testicular Axis in the Mozambique Tilapia Oreochromis mossambicus (Cichlidae)

Although fish are often exposed to food restrictions in natural or aquafarming conditions, the relationship between altered energy status and the reproduction is not well understood. The aim of the present investigation was to elucidate the effect of chronic food-deprivation on energy status and reproductive axis in male Mozambique tilapia Oreochromis mossambicus. The controls received food ad libitum, whereas the fish in the starvation group were deprived of food for 21 days. The liver showed significantly higher levels of gluconeogenesis and triglycerides, whereas the levels of blood glucose and total protein content in the liver were significantly lower in starved fish compared to controls. Furthermore, the mean numbers of different spermatogenic cells, such as spermatogonia-A, primary spermatocytes, secondary spermatocytes, early spermatids, and late spermatids were significantly lower, but the number of spermatogonia-B did not show a significant difference compared to controls. In starved fish, there was a significant increase in germ cell apoptosis at different stages of development concomitant with faintly immunoreactive androgen receptors in the Sertoli cells of the testis compared with controls. In addition, the percent areas of gonadotropin-releasing hormone—immunoreactive fibres and luteinizing hormone—immunoreactive content—in the proximal pars distalis part of the pituitary gland were significantly lower in starved fish compared with controls. Collectively, these results suggest that decreased energy status negatively affects the gonadotropin-releasing hormone—luteinizing hormone – testicular axis, leading to inhibition of spermatogenesis before entry of germ cells into meiosis through increased apoptosis and decreased expression of androgen receptors in the testis of the Mozambique tilapia.

DNA metabarcoding reveals the diet of the invasive fish Oreochromis mossambicus in mangroves of São Tomé Island (Gulf of Guinea)

AbstractInvasive species can trigger profound effects on recipient ecosystems, namely through the food web. Despite being recognized as one of the worst invasive species, little is known about the feeding ecology of the Mozambique tilapia Oreochromis mossambicus. To understand how this invasive species might impact food webs, we applied metabarcoding to analyze its diet’s composition in two African mangroves, in the Obô Natural Park in the oceanic island of São Tomé. Given the particular importance of mangroves as fish nurseries, we specifically aimed to determine if this invader might predate on other fish species. However, we found that tilapia were mostly phytoplanktivorous and indication on predation of other fish was very limited. Instead, due to their local high densities, tilapia may impact basal trophic levels and nutrient availability with the potential to cascade through the food web by means of bottom-up disruption. In addition, we recorded important changes in the taxonomic composition of the diet, linked to locations and life stages, suggesting that its opportunistic feeding associated with its aggressive territorial behavior may result in resource competition with native species with which it has overlapping dietary niches.

Chemical composition of Tithonia diversifolia (Hemsl.) and its effect on growth performance, feed efficiency and metabolic biochemistry of juvenile hybrid tilapia Oreochromis mossambicus × Oreochromis niloticus

The aquaculture due to the high cost and continued shortage of animal protein sources, the development of alternative plant protein sources has been one of the main challenges to establish sustainable aquaculture as economically viable. Objective of this investigation was to determine the chemical composition and effect of Tithonia diversifolia on the growth performance, feed efficiency and metabolic biochemistry of juveniles of Oreochromis mossambicus × Oreochromis niloticus. Five treatments were used: 0% (control), 4, 8, 12 and 16% levels of inclusion of T. diversifolia flour in diet to feed juvenile fish cultured in 15 plastic aquariums at a density of 15 fish/aquarium. The assay lasted eight weeks. The T. diversifolia flour was characterized for showing adequate levels of crude protein (21%), with low crude fat (4.5%) levels, neutral detergent fiber levels: 43.03% and acid detergent fiber: 24.40%. The growth performance presented significant differences (p˂0.05), for weight gain, day average weight gain (DAW), length gain, day average length gain (DAL), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and feed conversion ratio (FCR). In treatment with 16% of inclusion of T. diversifolia flour, values obtained for weight gain, DAW, SGR, FE and PER (15.88 g, 0.28 g. day-1, 2.03 %, 0.34 g.g-1 and 0.98, respectively), which did not differ with the control treatment, highlighting the benefits of T diversifolia flour. The metabolic biochemistry parameters experienced a decrease with the increase of T. diversifolia in diet, where the highest values of triglycerides, cholesterol, and glucose were for the control treatment (p <0.05), while the protein increased to 4% of the flour. T. diversifolia flour presents an adequate balance of nutrients for its chemical composition and amino acids, without causing negative effects on the growth performance, weight-length relationship, feed efficiency, survival and metabolic biochemistry.

Metazoan Parasites of Mozambique tilapia (Oreochromis mossambicus) Native to Lake Urema, Mozambique

Mozambique tilapia Oreochromis mossambicus (Peters, 1852), an important aquaculture species investigated herein, is at risk and listed as vulnerable on the IUCN Red List. During a preliminary survey conducted in 2011, 30 Mozambique tilapia from Lake Urema in Gorongosa National Park in central Mozambique, were examined for metazoan parasites. Two groups of ectoparasites were recovered consisting of two species of copepods and a monogenean. Endoparasites retrieved were in the larval stage and included one trematode and one nematode species. This study provides new parasite records for O. mossambicus in Mozambique and forms a baseline for monitoring against the presence of ichthyoparasites associated with the introduction in neighbouring systems of non-native fish such as Nile tilapia Oreochromis niloticus (Linnaeus, 1758), a fish of worldwide importance in capture fisheries and especially aquaculture.

Exopolysaccharides-Mediated ZnO Nanoparticles for the Treatment of Aquatic Diseases in Freshwater Fish Oreochromis mossambicus.

Bacterial fish disease outbreaks are a key concern for aquaculture. Complementary feed additives such as immunostimulants can serve as an ideal solution for disease prevention. Herein, we scrutinized the efficacy of exopolysaccharides (EPSs) from probiotic Bacillus licheniformis and EPS-mediated zinc oxide nanoparticles (EPS-ZnO NPs) for a diet to evaluate growth parameters, antioxidant enzyme activities, and immune stimulation together with disease resistance against Aeromonas hydrophila and Vibrio parahaemolyticus in Mozambique tilapia Oreochromis mossambicus. Fish were separated into seven groups, with six experimental groups fed with EPS and EPS-ZnO NPs at 2, 5, and 10 mg/g and a control fed a basal diet. The fish ingesting feed supplemented with EPS and EPS-ZnO NPs at 10 mg/g showed improved growth performance. Cellular and humoral-immunological parameters were tested in serum and mucus after 15 and 30 days of feeding. These parameters were substantially enriched with a 10 mg/g diet (p < 0.05) of EPS and EPS-ZnO NPs in comparison with the control. Furthermore, the EPS and EPS-ZnO NP supplemental diet actively enhanced the antioxidant response (glutathione peroxidase, superoxide dismutase, and catalase). In addition, the supplemental diet of EPS and EPS-ZnO NPs lowered the death rate and improved the disease resistance of O. mossambicus following assessment with A. hydrophila and V. parahaemolyticus at 50 µL. Hence, the overall results suggest that the supplemental diet of EPS and EPS-ZnO NPs might be used to ensure aquaculture feed additives.

Predicting the functional morphology of lotic and lentic populations of the invasive Mozambique tilapia Oreochromis mossambicus (Peters, 1852)

A better understanding of the mechanism which connects the morphology of fishes and their ecological performance is a major goal in evolutionary studies. As accepted widely, intra-species polymorphism mostly arises from divergent selection pressures between different environments. The present study sought to understand the functional morphological variations exhibited by Mozambique tilapia Oreochromis mossambicus (Peters, 1852) inhabiting heterogeneous habitats, using functional indices derived from the body. We found that O. mossambicus exhibited clear functional responses to divergent habitats indicating trait-habitat linkages. Fishes differed in three out of fifteen indices compared, which are mainly related to swimming performances. Fishes collected from the river possess more streamlined bodies and achieve higher values in indices related to swimming efficiencies. However, there were no significant intra-species differences in the indices related to feeding between habitats, indicating that functional divergences in O. mossambicus are mainly related to swimming and locomotion. The study confirmed that the morpho-functional variations observed in this species are primarily of selection pressure caused by habitat heterogeneities. The present findings further confirm our understanding of the predictive power of the trait-environment approach and indicate that fishes tend to change their traits related to swimming and foraging with changing ecological conditions of the habitat.Keywords: Cichlids, Ecomorphology, Functional traits, Phenotypic variation, Trophic polymorphism

Acute and Chronic Toxicity Effects of the Heptachlor Pesticide on Tilapia (Oreochromis mossambicus): Impact to Behavioral Patterns and Histopathological Responses

Manimekalai, D.; Srinivasan, A.; Padmavathy, P.; Jawahar, P.; George, R., and Arisekar, U., 2022. Acute and chronic toxicity effects of the heptachlor pesticide on tilapia (Oreochromis mossambicus): Impact to behavioral patterns and histopathological responses. Journal of Coastal Research, 38(5), 999–1010. Coconut Creek (Florida), ISSN 0749-0208. Heptachlor is an organochlorine (cyclodiene) insecticide that enters water bodies and affects aquatic organisms such as fishes and shellfishes. Due to its persistent nature, it spreads from the source of its use and pollutes the area. The toxic effect of heptachlor on histopathological changes in the gill, liver, kidney, and muscles of tilapia Oreochromis mossambicus were studied. The experimental fish were exposed to four concentrations of heptachlor, viz., 0.756, 1.513, 3.025, and 6.050 ppm, for a period of 96 hours during an acute toxicity test. In the current study, the lethal concentration (LC50) value of heptachlor on tilapia at 96 hours was calculated as 4.006 ppm. Fish were subjected to three different concentrations of heptachlor (0.2003, 0.4006, and 0.8012 ppm) based on the LC50 value to study the long-term effect of heptachlor. Histological changes such as lamellar fusion, lamellar cell hyperplasia, degenerated secondary gill lamellae; Bowman's space dilation and renal tubules detachment; hepatic cells death, melanomacrophage formation, and multifocal degeneration of myocytes; and myoepithelium vacuolation were observed in the gill, kidney, liver, and muscles, respectively, during acute and chronic exposure to heptachlor. The toxicity study revealed that the heptachlor pesticide is highly toxic to tilapia even at a minimum concentration of 0.756 ppm. Hence, it is suggested that care must be taken not to allow the entry of pesticides into the habitat of fishes.

Energy utilization during ovarian development of the cichlid fish Oreochromis mossambicus (Peters) inhabiting a perennial lentic water body in Bangalore, India.

Mozambique tilapia Oreochromis mossambicus (Peters) is an invasive fish and a continuous breeder in inland waters of India. Present investigation highlights the distinct developmental stages of developing ovary and associated changes in the energy content. This investigation helps to understand the allocation of energy for development of eggs, prespawn and also oral brooding by the female. Although it is a continuous breeder, based on size of the ovary, number of eggs, their size and energy content, immature, early maturing, developing, prespawning and spawning stages are clearly noticed. Egg diameter during development of ovary varied between 0.31 mm (immature) and 2.21 mm (spawning). Energy content of ovary from immature to spawning stage ranged from 20.7515 kJ g-1 dry ovary to 31.1560 kJ g-1 dry ovary. Nearly 28.73% of energy content of ovary is expended for spawning. Similarly, yolk-sac fry utilized nearly 25.85% of energy of the fertilized egg for its development. Energy content of ovary of mouth-brooding female averaged 22.9528 kJ g-1 dry ovary, which is comparable to energy content of early maturing stage of ovary (24.5558 kJ g-1 dry ovary). A strong correlation between body weight and energy content of the developing ovary (P < 0.01), and between ovary weight and energy content of ovary (P < 0.01), was evident. During mouth-brooding, the fish continues to allocate energy to its developing ovary. Energy investment by the fish is the result of simultaneous processes associated with gonadal and somatic energy. As body size growth and gonadal development are interconnected, information on energy utilization by an iteroparous mouth-brooding fish could provide the pattern of energy allocation during ovarian developmental phase. Further details of energy utilization, as explained in this paper, could be used as one of the factors to predict the efficiency of fish production.

The Influence of Kappa Opioid Receptor Antagonist 5'-Guanidinonaltrindole during Reproductive Stress Response in the Mozambique Tilapia Oreochromis mossambicus (Cichlidae)

The Influence of Kappa Opioid Receptor Antagonist 5'-Guanidinonaltrindole during Reproductive Stress Response in the Mozambique Tilapia Oreochromis mossambicus (Cichlidae)

Effect of polysaccharides derived from brown macroalgae Sargassum dentifolium on growth performance, serum biochemical, digestive histology and enzyme activity of hybrid red tilapia

The present trial conducted to examine the impact of dietary red seaweeds, Sargassum dentifolium polysaccharides supplementation on growth induces, hematological and histological indicators of the hybrid red tilapia Oreochromis mossambicus × Oreochromis niloticus fingerlings. A total of 240 hybrid red tilapia fingerlings with an average body weight of 7.50 ± 0.01 g were divided into four experimental treatments (three replicates each). Four identical isonitrogenous isoenergetic diets except the variation of polysaccharide (SP) levels were formulated. The basal experimental diet (control diet) had no seaweed polysaccharide added (SP0). Diets 2–4 (SP1; SP2 and SP3) was formulated to contained seaweed polysaccharide at levels of 10, 20, and 30 g/kg diet, respectively. Growth performance and feed utilization efficiency of hybrid Red tilapia were significantly (P ≤ 0.05) higher in all treatments receiving SP supplemented-diets than the control diet. The red blood cells (RBCs), hemoglobin (Hb) and hematocrit (Hct, %) values differed significantly (P ≤ 0.05) between the control and fish fed various SP supplemented diets. Considering the dietary SP supplementation, a clear higher trend values of RBC was observed with increasing dietary SP inclusion. Lipase activity recorded the highest values with the fish fed diet supplemented with SP at a level of 20 g/kg-1 associated with the lower significant values amylase activity compared to other treatments. Dietary SP supplementation had no effect on total plasma protein, albumin and globulin levels. Fish fed SP2 diet had an increase in GOT, triglycerides. Fish fed SP3 recorded the lowest value of total cholesterol and LDL when compared to other diets. No abnormal or histological changes were detected in sections of liver, stomach and intestine of red tilapia fed different dietary supplemented with SP levels. The findings of current trial revealed that hybrid Red tilapia fed diets containing red seaweeds, polysaccharides for 12 weeks had enhanced performance, feed conversion ratio and hematological indices.

Behavioural Responses and Mortality of Mozambique Tilapia Oreochromis mossambicus to Three Commonly Used Macadamia Plantation Pesticides

The use of pesticides in agricultural systems may have deleterious effects on surrounding environments. Aquatic systems are no exception and are increasingly polluted through the leaching of pesticides from agricultural activities. However, the pesticide pollution effects on key aquatic species have not been studied in many regions. In southern Africa, increasing pesticide use associated with macadamia tree Macadamia integrifolia farming presents a growing risk to surrounding aquatic ecosystems. This study assessed behavioural responses of an important and widely-distributed freshwater fish, Mozambique tilapia Oreochromis mossambicus, following exposure to three commonly used macadamia pesticides (i.e., Karate Zeon 10 CS, Mulan 20 SP, Pyrinex 250 CS) at different concentrations (0.7–200 µL, 0.3–1000 mg, and 0.7–8750 µL, respectively) over 24 h. Behavioural responses, i.e., swimming erratically, surfacing, vertical positioning, loss of equilibrium, being motionless and mortality were observed after pesticides exposure. Lethal dose 50 (LD50) values of Karate Zeon 10 CS, Mulan 20 SP and Pyrinex 250 CS were 2.1 µL (per water litre dilution—WLD), 5.2 mg (WLD) and 21.5 µL (WLD), respectively. These concentrations are therefore expressed as a maximal threshold usage in the environment around macadamia farms and a minimum distance of the plantations to water systems should be considered. Further studies should examine effects on other fish species and aquatic invertebrates to inform on pesticide pollution threats and mitigation plans for the region.

Tissue Repairing Activity of Glycosmis pentaphylla Leaf Extract on Oreochromis mossambicus Against Arsenic Induced Toxicity

Acute toxicity of arsenic to Tilapia (Oreochromis mossambicus) and tissue repairing activity of Glycosmis pentaphylla leaf extract and its histological impacts on gill, liver, and kidney tissues were evaluated. Fish were divided into six groups viz. control, group 1, group 2, group 3, group 4, and group 5. 4.87 ppm of NaAsO2 was administrated in group 1, group 3, and group 5. In group 3, after arsenic exposure, 2.5 g of leaf extract of Glycosmis pentaphylla per kg of fish food was added. In group 5, 5g of G. pentaphylla leaf extract per kg of fish food was added. In group 2, 2.5 g of leaf extract per kg of fish food was added and in group 4, 5g leaf extract per kg of fish food was added. The control group showed normal histology of the gill, liver, and kidney. The histological observations revealed the tissue repairing activities in group 2 fish’s gill, liver, and kidney. These results revealed the protective and tissue repairing potential of G. pentaphylla as a feed supplement against NaAsO2 induced toxicity.

Melanin-concentrating hormone interferes with the hypothalamic-pituitary-gonad axis in the Mozambique tilapia

This study was conducted to elucidate the influence of melanin-concentrating hormone (MCH) along the reproductive-axis in the female tilapia Oreochromis mossambicus. Administration of MCH (4 μg / 0.1 ml saline) for 22 days resulted in significantly lower gonadosomatic index compared to controls. Significant reduction in the mean numbers of follicles at different stages of development such as previtellogenic (stages I-III), vitellogenic (stage IV) and preovulatory (stage V) follicles was observed in MCH-treated fish compared with controls. On the other hand, the rate of atresia was significantly higher in follicles at stages II, III and IV in MCH-treated fish. In addition, in the pituitary gland, sparsely labelled gonadotropin releasing hormone (GnRH)-immunoreactive fibres were observed in MCH-treated fish in contrast to their intense labelling in controls. The serum level of luteinizing hormone (LH) showed significant decrease, but the serum cortisol level rose significantly following MCH treatment compared to those of controls. Collectively, these results indicate for the first time, that MCH treatment blocks follicular development during the ovarian cycle, possibly through the suppression of GnRH-LH axis in fish. The results also indicate that MCH may activate the stress-axis pathway in fish.