Browsing by Author "Omeje, Victor Okonkwo"

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    Effect of pawpaw (Carica papaya) seed meal on sex determination, growth, and survival, of Oreochromis mossambicus fry
    (AquacultureHub Inc, 2018) Omeje, Victor Okonkwo; Lambrechts, Helet; Brink, Daniel
    The production of monosex tilapia populations is a potential and effective solution for the precocious breeding and indiscriminate spawning that occurs in mixed sex culture systems. This study investigated the possibility of using Carica papaya seed meal (PSM) to skew the sex ratio of sexually undifferentiated Oreochromis mossambicus fry. A total of 2160 fry were used in the study, and fish were allocated to 12 treatment groups in triplicate, with 60 fish per replicate. The experimental diets fed included a basal diet (BD), 60mg methyl testosterone/kg BD, and 5 treatment diets containing 10, 15, 20, 25 and 30g PSM/kg of the BD, respectively for 30 and 120 days. PSM was able to skew the sex ratio in favor of males, with the proportion of males to females increasing with an increase in PSM content of the diet. The highest percentage phenotypic males (77.8%) induced by the PSM was obtained among the groups that received 20g and 30g PSM/kg BD. The growth and survival rates of the fish were not influenced by any of the treatment diets. Fragmentation of ovarian nuclei, hypertrophy of interstitial cells, and vacuolization of hepatocytes were observed in the gonads and hepatic tissues. The study demonstrated that an inclusion level of 20g PSM/kg BD was effective in converting females to phenotypic males.
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    Effect of Pawpaw (Carica papaya) seed meal on the reproductive, endocrine and immune system of Mozambique tilapia (Oreochromis mossambicus)
    (Stellenbosch : Stellenbosch University, 2016-03) Omeje, Victor Okonkwo; Lambrechts, Helet; Brink, Danie; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Aquaculture, the farming of aquatic animals and plants, has the potential to solve the problems of dwindling catches from artisanal fisheries as a result of overfishing and habitat degradation. Tilapia species is one of the most cultured food fish worldwide, second only to carp. In Sub-Saharan Africa, which is in dire need of food security, tilapia has the potential to be a cheap source of protein, which through its cultivation, can contribute to poverty alleviation among the rural poor communities. Tilapia breeds effortlessly in captivity, with this attribute which is considered as the “Achilles heel” of the species, because it predisposes pond systems to overcrowding and low weight at harvest. Efforts to mitigate this shortcoming include mono-sex culture of all-males using exogenous hormone to reverse the sex of sexually undifferentiated fish. This is premised on the fact that improvement in the growth by mono-sex culture will lead to shortened production times and a more uniform weight at harvest, which will ultimately benefit the producers. However, the use of exogenous hormones in aquaculture has recently raised concerns about the effect on farm workers, consumers and on the environment. Recently research has focused on the use of substances of plants origin which mimic the action of hormones as a potential approach to achieve sex reversal in fish. Pawpaw (Carica papaya) seed meal (PSM) contains phytochemicals that hold great promise as a sex reversal and a reproductive inhibition agent in aquaculture. The objective of this study was to determine the optimum inclusion levels of PSM that will produce the highest percentage of male brood when included in the diet of sexually undifferentiated Mozambique tilapia (Oreochromis mossambicus; OM) fry of approximately one to two weeks old. Furthermore the study investigated the effects of the PSM on the reproductive hormone profile, haematological and serum biochemical parameters, and gonad and liver integrity of pre-vitellogenic OM. At an inclusion level of 10 g/kg of basal diet, PSM was able to skew the sex ratio in favour of males (60% males to 40% females). The proportion of males increased with an increasing dosage of PSM, with the maximum masculinization achieved at an inclusion level of 20 g/kg BD, resulting in 77.8% males produced. When the masculinization success was compared in terms of the duration of the feeding regimes of one and four months, no significant differences were observed in terms of the number of males produced. The inclusion of PSM did not affect the growth and survival rates, neither did it affect the Fulton’s condition factor of the treated fish. It was found that the PSM investigated lowered the level of plasma 17β- estradiol in female fish but had no effect on the level of the same hormone in males. The plasma levels of 11-ketotestosterone was not affected in both genders. The gonad weight and gonado-somatic index of the male fish were not affected by treatment with PSM, while the gonad weight, GSI, fecundity and egg diameter of the treated females were lower than those of the control. Some of the changes induced returned to normal on cessation of treatment suggesting a reversible reproductive inhibition by PSM. Haematological and biochemical profiles of different treatment groups did not differ throughout the course of the investigation. Liver weight and hepato-somatic index of the treated fish were comparable to those of the control. Histological observations showed minor alterations in the architecture of the liver, with degeneration and vacuolization of hepatocytes in less than 10% of the members in the group fed 30 g of PSM /kg of basal diet for 60 days. However this was not noticed among the group fed 30 g of PSM/kg of basal diet for 30 days, suggesting a possible reversibility of the lesion on withdrawal of treatment. The current research has clearly demonstrated the potential of PSM as a fertility inhibitor and sex reversal agent in OM, with potential application in rural fish farming and feed manufacturing industries. The possibility exist that some of the findings can be adapted to be applicable in other tilapia species like O. niloticus or Sarotheridon galilaeus which together with O. mossambicus constitute the most cultured species in Sub-Saharan Africa.
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    Hepatic and haemato-biochemical alterations in juvenile Mozambique tilapia (oreochromis mossambicus) on pawpaw (carica papaya) seed meal
    (Canadian Center of Science and Education, 2019-06-15) Omeje, Victor Okonkwo; Lambrechts, Helet; Brink, Danie
    Pawpaw seed meal (PSM) can be used as an antifertility agent in animals, however there is no information on its potential toxicological effect on Mozambique tilapia (O. mossambicus). In this study the effect of PSM on the liver, blood haematological and biochemical parameters of O. mossambicus juveniles was assessed to ascertain its suitability as a reproductive suppressant. The PSM was administered at an inclusion level of 10 g and 30 g/kg of a commercial tilapia diet (basal diet, BD) for 30 and 60 days, respectively. The potential toxicological effect was assessed by determining the extent of change in the normal haematological (RBC count, haematocrit, haemoglobin, MCV, MCH, MCHC, thrombocyte count, absolute WBC and differential cell counts) and biochemical (cholesterol, total protein, albumin, globulin and glucose) parameters. Haematological and biochemical profiles of different treatment groups did not differ throughout the course of the investigation. Liver weight and hepatosomatic index values of the treated fish were comparable to those of the control. The absence of any effect of the blood parameters measured in this study also indicate that PSM has no compromising influence on the immune system of the fish, indicating that PSM can be considered as a safe alternative to induce masculinization in Mozambique tilapia, and therefore act as a reproductive inhibitor.
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    Hormonal profile and reproductive parameters of pre-vitellogenic mozambique tilapia (oreochromis mossambicus) on pawpaw (carica papaya) seed meal
    (Canadian Center of Science and Education, 2019-06-15) Omeje, Victor Okonkwo; Lambrechts, Helet; Brink, Danie
    The use of phytochemicals to control precocious maturation and indiscriminate spawning among tilapia species is an important issue in aquaculture. This study investigated the influence of pawpaw (Carica papaya) seed meal on the reproductive performance, and the sex hormone profile of sexually immature Mozambique tilapia (Oreochromis mossambicus). Pawpaw seed meal (PSM) were included in a tilapia commercial diet (basal diet) at an inclusion level of 0 PSM, 10 PSM and 30 PSM g/kg of the basal diet (BD), respectively, and fed to immature O. mossambicus for a period of 30 and 60 days, respectively. Enzyme-linked immune-sorbent assay (ELISA) procedures were used to quantify the plasma levels of 17β-estradiol and 11-ketotestosterone. The inclusion of PSM did not affect the growth and survival rate of the O. mossambicus. The plasma levels of 11-ketotestosterone did not differ among the treatment groups. The 17β-estradiol levels of female fish that received 30 PSM g/kg BD for 60 days were significantly lower (p < 0.05) than the levels reported for females that were not fed the PSM. In females, the PSM reduced the gonad weight, GSI, fecundity and egg diameter of fish. The study concludes that pawpaw seed meal affected the reproductive function of the female O. mossambicus though the changes were reversible.
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    Use of pawpaw (Carica papaya) seed in tilapia sex reversal
    (Reviews in Agricultural Science, 2020-10-18) Omeje, Victor Okonkwo; Lambrechts, Helet; Brink, Danie
    Tilapia breeds effortlessly in captivity, with this attribute which is considered as the “Achilles heel” of the species, because it predisposes pond systems to overcrowding and low weight at harvest. Efforts to mitigate this shortcoming include mono-sex culture using exogenous hormone to reverse the sex of sexually undifferentiated fish. This is premised on the fact that improvement in the growth by mono-sex culture will lead to shortened production times and a more uniform weight at harvest, which will ultimately benefit the producers. However, the use of exogenous hormones in aquaculture has recently raised concerns about the effect on farm workers, consumers and on the environment. Recently research has focused on the use of substances of plants origin which mimic the action of hormones as a potential approach to achieve sex reversal in fish. Pawpaw (Carica papaya) seed contains phytochemicals that hold great promise as a sex reversal and a reproductive inhibition agent in aquaculture. The purpose of this study was to conduct a systematic review of the relevant literature on the possibility of using a less harmful phytochemicals abundant in the plant to effect sex reversal of sexually undifferentiated tilapia.