Effect of Pawpaw (Carica papaya) seed meal on the reproductive, endocrine and immune system of Mozambique tilapia (Oreochromis mossambicus)

Omeje, Victor Okonkwo (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANSE OPSOMMING: Akwakultuur, die boerdery van akwatiese diere en plante, het die potensiaal om die probleme van die kwynende vangste van ambagsvissers, wat die gevolg is van oorbenutting van visbronne en habitat vernietiging, op te los. Tilapia spesies is een van die mees gewilde voedselvis spesies wêreldwyd, naas karp. In Sub-Sahara Afrika, wat ʼn dringende behoefte aan voedselsekuriteit ervaar, verteenwoordig tilapia 'n goedkoop bron van proteïen en wat deur die produksie daarvan, die potensiaal het om by te dra om armoede verligting in landelike gemeenskappe. Tilapia spesies teel moeiteloos in aanhouding, maar hierdie eienskap word ook as die "Achilleshiel" van die spesie beskou, want dit lei tot oorbevolking van damme en ʼn lae eindgewig wanneer die vis geoes word. Pogings om hierdie tekortkoming aan te spreek sluit die produksie van enkelgeslag groepe, waar die geslagsdifferensiasie van ongedifferensieerde vingerlinge deur middel van die toediening van eksogene hormone gemanipuleer word. Die beginsel is gebaseer op die feit dat die verbetering in die groei in enkelgeslag groepe sal lei tot ʼn verkorte produksietydperk en 'n meer eenvormige gewig by die oes, wat uiteindelik tot voordeel van die produsente sal wees. Die gebruik van eksogene hormone in akwakultuur het egter onlangs kommer veroorsaak as gevolg van die potensiële invloed op plaaswerkers, verbruikers en die omgewing. Onlangse navorsing het gefokus op die gebruik van middels van plantoorsprong wat in die plek van eksogene hormone gebruik kan word om die manipulasie van geslag en die uiteindelike produksie van enkelgeslag groepe, moontlik te maak. Papaja (Carica papaya) meel gemaak van papaja pitte (PSM) bevat fitochemikalieë wat die potensiaal het om die geslag van ongedifferensieerde vingerlinge te manipuleer om enkelgeslag groepe te produseer en so dus as ʼn reproduksieonderdrukkende stof in akwakultuur sisteme gebruik te word. Die doel van hierdie studie was om die optimale insluitingsvlak van PSM, wanneer dit as deel van die dieet van ongedifferensieerde Mosambiek tilapia (Oreochromis mossambicus; OM) ingesluit word, wat die hoogste persentasie manlike vis tot gevolg sal hê. Verder het die studie die invloed van die PSM op die reproduksiehormoon profiel, hematologiese - en serum biochemiese parameters, asook geslagsklier- en lewer integriteit van pre-vitellogeniese OM bepaal. Die PSM het by 'n insluitingsvlak van 10 g PSM/kg basale dieet (BD) die geslagsverhouding ten gunste van manlike vis verander (d.i. 60% manlik vs. 40% vroulik). Die verhouding van manlike vis het toegeneem met 'n toenemende dosis PSM, met die maksimum vermanliking van 77.8% wat met 'n insluitingsvlak van 20 g PSM/kg BD verkry is. Wanneer die vermanliking sukses vergelyk is in terme van die duur van die behandelingstydperk van 1 en 4 maande onderskeidelik, is geen betekenisvolle verskille waargeneem in terme van die persentasie vermanliking nie. Die insluiting van PSM het geen invloed op die groei en oorlewing van OM gehad nie en dit het ook geen invloed op die Fulton kondisiefaktor van die behandelde vis gehad nie. Daar is gevind dat die PSM die plasmavlak van 17β-oestradiol in vroulike vis verlaag het, maar dit het geen effek op dié hormoon se vlakke in die manlike vis gehad nie. Geen invloed van die PSM is op die plasmavlakke van 11-ketotestosteroon in beide geslagte waargeneem nie. Die gonade gewig en die gonado-somatiese indeks (GSI) van die manlike vis is nie deur die PSM behandeling beïnvloed nie, terwyl die gonade gewig, GSI, vrugbaarheid en eier deursneë van die wyfie visse laer as dié van die wyfies in die kontrole groep was. Met staking van die PSM behandeling is daar ʼn omkering van die inhibering van reproduksie wat deur die PSM veroorsaak is, waargeneem. Die hematologiese en biochemiese profiel van die onderskeie behandelingsgroepe het nie betekenisvol verskil deur die verloop van die ondersoek nie. Lewergewig en die hepato-somatiese indeks van die behandelde vis was vergelykbaar met dié van die kontrole groep. Histologiese waarnemings het klein veranderinge in die argitektuur van die lewer, d.i. degenerasie van en die vorming van vakuole in hepatosiete in minder as 10% van die visse wat 30 g PSM/kg BD vir 60 dae gevoer is. Hierdie defekte is egter nie waargeneem by visse wat 30g PSM/kg BD vir 30 dae ontvang het nie, wat dus dui op 'n moontlike omkeerbaarheid van die lewerskade met onttrekking van die behandeling. Die studie het duidelik getoon dat PSM effektief gebruik kan word om reproduksie te onderdruk as ook om vermanliking van groepe moontlik te maak, met hierdie twee bevindinge wat praktiese toepassing in landelike visboerderysisteme en voervervaardigingsbedrywe het. Die moontlikheid bestaan dat sommige van die bevindinge aangepas kan word vir ander tilapia spesies soos O. niloticus of Sarotheridon galilaeus, wat saam met O. mossambicus die volopste in Sub-Sahara Afrika.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98749
This item appears in the following collections: