Comparative assessment of the production performances of different strains of nile tilapia and the evaluation of genotype × environment interaction

Binyotubo, Omowumi Ibijoke (2017-03)

Thesis (PhDAgric)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Aquaculture is acknowledged worldwide as a major contributor to food security. Nile tilapia (Oreochromis niloticus) is the second most produced freshwater fish, and an important source of affordable animal protein in Africa. Tilapia production in Africa is characterised by traditional small-scale subsistence farming systems and more recently the introduction of large-scale intensive farming systems. The efficiency of tilapia production can be improved by farming with genetically improved strains that are developed for particular types of production systems. Genetically improved tilapia strains have been developed under controlled conditions, without proper assessment of their suitability for culture in both intensive and extensive systems, where conditions likely may differ from which the strains were developed in. It is important to determine the potential effect of genotype X environment interaction (GxE) on the performance of these improved genotypes in production systems in Africa. To date the potential GxE effect on the production performance of improved Nile tilapia genotypes in different production systems has not been investigated, and validated in Africa. This study therefore assessed the performance of six unrelated strains of Nile tilapia to determine the possible influence of GxE on the growth rate, proximate carcass composition and haematological parameters. Unrelated strains were randomly allocated to a high input systems (represented by a high energy (HE) diet in the form of a commercial feed), and a low input system (represented by a natural low energy (LE) diet in the form of duckweed (Lemna minor) during two trials conducted during summer (Experiment 1) and winter (Experiment 2), respectively. The strains (displayed significant differences in relation to a wide range of growth parameters for both treatments (diets) and seasons, with the GIFT strain having the best overall performance. The growth rate of strains fed the HE diet was significantly higher than strains fed the LE diet, for all strains during both seasons. There was no significant difference in yield between strains and treatments for Experiment 1. There was significant difference observed in Experiment 2, where the Red strain was characterized by lower yields. The condition factor for both diets was within acceptable ranges, and no difference in survival was observed in relation to strains and diets. The HE diet resulted in a significantly higher carcass fat content, whereas the LE diet result a higher carcass ash and moisture (90 – 95%) content. Diet did not influence carcass protein content. Red blood cell (RBC), haemoglobin (HB) and hematocrit (HCT) values did not differ between diets, while significant differences were observed for mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), white blood cell (WBC), neutrophils (NEU), eosinophils (EOS), and basophils (BASO). The study reports on the first phenotypic biserial correlations for Nile tilapia for growth parameters, with all bi-serial correlations reported all growth traits for Experiment 1 being above the threshold of 0.8, indicating an absence of GxE interaction. The bi-serial correlations calculated for Experiment 2 similarly indicated a level of non-significant GxE for most strains, with Strain S6, where a weak degree of GxE was observed (0.729-0.777). In some cases, re-ranking was observed, however, this re-ranking was found to be not significant. This study confirmed significant differences between the strains in relation to various growth parameters, although there was no clear indication of GxE effects associated with the LE and HE diets. The superior strains may therefore be recommended for application in relation to both treatments applied in this study. GIFT strain (S4) perform significantly better than other strains in the wider coverage of this experiment. The findings of this study indicated that it is important to determine the GxE influence on the performance of improved genotypes, especially when they are propagated for use in low input, small-scale production systems, which may represent conditions that differ from those under which the genotypes have been developed in. A greater awareness also needs to be created amongst subsistence and commercial tilapia farmers in Africa about the possible effect of GxE on the production performance of wild and genetically improved genotypes under different environmental conditions.

AFRIKAANSE OPSOMMING: Akwakultuur word wêreldwyd erken as 'n belangrike bydraer tot voedselsekerheid. Nyl tilapia (Oreochromis niloticus) is die tweede mees geproduseerde varswatervis, en 'n belangrike bron van bekostigbare diereproteïen in Afrika. Tilapia produksie in Afrika word gekenmerk deur tradisionele kleinskaalse bestaansboerderystelsels en meer onlangs die bekendstelling van grootskaalse intensiewe boerderystelsels. Die doeltreffendheid van tilapia produksie kan verbeter kan word deur die gebruik van geneties verbeterde stamme wat vir spesifieke tipes produksiestelsels ontwikkel is. Geneties verbeterde tilapia genotipes is ontwikkel onder beheerde toestande, sonder behoorlike beoordeling van hulle geskiktheid vir kultuur in beide intensiewe en ekstensiewe stelsels, waar toestande waarskynlik kan verskil van dit waaronder die genotipes ontwikkel is. Dit is belangrik om die potensiële invloed van genotipe x omgewing interaksie (GxE) op die prestasie van hierdie verbeterde genotipes in produksiestelsels in Afrika te bepaal. Tans is die effek van GxE op die produksie prestasie van verbeterde Nyl tilapia genotipes in verskillende produksiestelsels nog nie ondersoek en bevestig vir produksietoestande in Afrika nie. Hierdie studie evalueer dus die prestasie van ses onverwante genotipes van Nyl tilapia om die moontlike invloed van GxE op die groeitempo, karkas samestelling en hematologiese parameters te bepaal. Onverwante bloedlyne is ewekansig toegewys aan 'n hoë inset stelsel (verteenwoordig deur 'n hoë-energie (HE) dieet in die vorm van 'n kommersiële voer) en 'n lae inset stelsel (verteenwoordig deur 'n natuurlike lae energie (LE) dieet in die vorm van duckweed (Lemna minor) tydens twee proewe wat onderskeidelik in die somer (Eksperiment 1) en winter (Eksperiment 2) uitgevoer is. Die genotipes het betekenisvol verskil in terme van 'n wye verskeidenheid van groei parameters vir beide behandelings (dieet) en seisoene, met die GIFT genotipe wat algeheel die beste presteer het. Die groeitempo van genotipes wat die HE dieet ontvang het, was aansienlik hoër as die genotipes wat die LE dieet ontvang het, vir alle genotipes en vir beide seisoene. Daar was geen beduidende verskil in opbrengs tussen genotipes en behandelings in Eksperiment 1 nie. Daar is ʼn beduidende verskil waargeneem in Eksperiment 2, waar die Rooi genotipe gekenmerk is deur ʼn laer opbrengs. Die kondisiefaktor vir beide diëte was binne aanvaarbare grense vir Nyl tilapia en geen verskil is in die oorlewing met betrekking tot genotipe en dieet waargeneem nie. Die HE dieet het 'n aansienlik hoër karkasvetinhoud tot gevolg gehad, terwyl die LE dieet lei 'n hoër karkasvog inhoud gelei het (90-95%). Dieet het nie die karkasproteïeninhoud beïnvloed nie. Rooibloedsel- (RBS), hemoglobien- (HB) en hematokrit (HCT) waardes het nie tussen diëte verskil nie, terwyl beduidende verskille waargeneem is vir gemiddelde korpuskulêre volume (MCV), gemiddelde korpuskulêre hemoglobien (MCH), gemiddelde korpuskulêre hemoglobien konsentrasie (MCHC), witbloedsel- (WBC), neutrofiel- (NEU), eosinofiel- (EOS) en basofiel (BASO) tellings. Die studie doen verslag oor die eerste fenotipiese twee-reeks (biserial) korrelasies vir Nyl tilapia vir groei parameters, met die twee-reeks korrelasies vir groei eienskappe vir Eksperiment 1 wat bo die drumpel van 0.8 was wat dui op 'n gebrek aan GxE interaksie. Die twee-reeks korrelasies bereken vir Eksperiment 2 het insgelyks aangedui 'n vlak van nie-beduidende GxE vir die meeste stamme waargeneem is, met Genotipe S6 waar 'n swak graad van GxE waargeneem is (0.729-0.777). In sommige gevalle is die rangorde van die genotipes aangepas, maar hierdie aanpassing was nie betekenisvol nie. Hierdie studie bevestig beduidende verskille tussen die genotipes met betrekking tot verskillende groei parameters, hoewel daar nie 'n duidelike aanduiding van GxE effekte waargeneem is wat verband hou met die HE en LE dieet nie. Die meer doeltreffende genotipes kan dus aanbeveel word vir gebruik in toestande soortgelyk aan hierdie studie. Die GIFT genotipe het aansienlik beter as die ander genotipes in die wyer opset van die eksperimente in dié studie gedoen. Die bevindinge van hierdie studie dui daarop dat dit belangrik is om die GxE invloed op die prestasie van verbeterde genotipes, veral wanneer hulle aanbeveel word vir gebruik in lae inset, kleinskaalse produksiestelsels, wat eise aan genotipe kan stel wat verskil van dié waaronder die bepaal genotipe ontwikkel is. 'n Groter bewustheid moet ook geskep word onder bestaans- en kommersiële tilapia boere in Afrika oor die moontlike uitwerking van GxE op die produksieprestasie van wilde (onverbeterde) en geneties verbeterde genotipes onder verskillende omgewingstoestande.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101266
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