Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    A systematic literature review of the major factors causing yield gap by affecting growth, feed conversion ratio and survival in Nile tilapia (Oreochromis niloticus).
    Mengistu, Samuel ; Mulder, H.A. ; Benzie, John A.H. ; Komen, J. - \ 2020
    Reviews in Aquaculture 12 (2020)2. - ISSN 1753-5123 - p. 524 - 541.
    Productivity among small‐ and medium‐scale tilapia farms varies considerably. The difference between the best performers and lower ones (yield gap), is affected by differences in growth rate and feed conversion ratio (FCR). FCR at the farm level is strongly influenced by survival of fish. In this study a systematic literature review of two databases (ASFA and CAB‐Abstracts) identified 1973 potentially relevant articles. Data from 32 articles that met the inclusion criteria were analysed using linear mixed models for the most important factors with significant contributions to growth [investigated through analysis of the thermal growth coefficient (TGC)], survival and FCR of Nile tilapia. Increasing crude protein (CP), dissolved oxygen (DO) and pH significantly decreased FCR and increased TGC. Increasing stocking weight (SW) significantly improved both FCR and survival. Temperature had the largest effect on FCR followed by DO, pH and CP. DO had the largest effect on TGC followed by CP and pH. This study confirms that the optimal rearing temperature for Nile tilapia is between 27 and 32°C. Improving management to optimize DO (> 5 mg/L), stocking density (3–5 fish/m2), SW (> 10 g) and CP (25 − 30%) will improve performance and survival in small‐ and medium‐scale tilapia farming. However, it is hard to influence temperature in ponds and cages while DO is largely influenced by aeration. Since many small‐ and medium‐sized farms do not have aeration, these major tilapia farming systems could benefit from genetically improved strains selected for resilience to highly fluctuating diurnal temperature and DO levels.
    Non-aerated ponds reduces variances and heritabilities compared to aerated ponds in Nile tilapia
    Mengistu, Samuel ; Mulder, H.A. ; Benzie, John A.H. ; Khaw, H.L. ; Komen, J. - \ 2019
    In: Book of Abstracts of the 70th Annual Meeting of the European Federation of Animal Science. - Wageningen Academic Publishers (EAAP Book of Abstracts ) - ISBN 9789086868902 - p. 519 - 519.

    Genotype by environment interaction for growth and survival of Nile tilapia in aerated and non-aerated ponds
    Mengistu, Samuel ; Komen, J. ; Benzie, John A.H. ; Khaw, H.L. ; Mulder, H.A. - \ 2018
    In: Session abstracts ISGA 2018. - - 1 p.
    Improving feed efficiency in fish using selective breeding : A review
    Verdal, Hugues de; Komen, Hans ; Quillet, Edwige ; Chatain, Béatrice ; Allal, François ; Benzie, John A.H. ; Vandeputte, Marc - \ 2018
    Reviews in Aquaculture 10 (2018)4. - ISSN 1753-5123 - p. 833 - 851.
    Feed conversion ratio - Feed efficiency - Feed intake - Fish - Genetics - Selection

    Improving feed efficiency (FE) is key to reducing production costs in aquaculture and to achieving sustainability for the aquaculture industry. Feed costs account for 30-70% of total production costs in aquaculture; much work has been done on nutritional and husbandry approaches to improve FE but only a limited amount of research has been devoted to using genetics, despite its potential. This paper reviews past work to improve FE in fish using selective breeding and assess future directions. Direct selection on FE traits requires methods to measure individual feed consumption and estimate FE efficiently and accurately. This is particularly difficult to do in fish because of the environment in which they live. Many of the published studies on FE were found to be inaccurate because of methodological problems. The relatively low heritability estimates of FE traits in fish published to date are probably partly as a result of inaccurate measurements of feed intake. Improving ways to measure the individual feed intake with high accuracy will be critical to the successful application of genetics to improving FE. Indirect selection criteria that could be used to improve FE (including growth after starvation/refeeding, body composition, neuropeptides or hormone levels) are discussed. Promising approaches to measuring feed intake accurately that may enable these studies to be undertaken are identified. More work using these will be needed prior to assessing the practicality of the introduction of direct or indirect traits for FE in fish genetic improvement programmes.

    A systematic review of management factors affecting growth, feed conversion ratio and survival in Nile tilapia
    Mengistu, Samuel ; Mulder, H.A. ; Benzie, John A.H. ; Komen, J. - \ 2017
    In: International Conference and Exposition EAS. - - p. 753 - 754.
    Introduction
    Currently many small and medium sized tilapia farms in developing countries underperform in terms of feed conversion ratio (FCR), despite the use of genetically improved strains of tilapia such as GIFT. The variable and often lower production in commercial environments compared to nucleus selection environments is a major bottleneck to increase productivity in tilapia farming. Feed cost is the major variable cost in fish farming (El-Sayed, 1999, Craig, 2009) and therefore this underperformance affects the profitability of fish farms negatively. This so-called yield gap has severe consequences for the effectiveness of breeding programs. The objective of this review was to analyse the most important environmental and management factors with significant contributions to growth, increased mortality and reduced feed efficiency of Nile tilapia.

    Materials and methods
    We conducted a systematic literature search on two data bases ASFA and CAB-Abstract on the 7th of July 2016. The search resulted in 1973 potentially relevant articles from which 59 articles met the inclusion criteria. After categorizing the studies based on the factors they investigated, we extracted data on the following variables: stocking density, photoperiod, culture unit, strain, whether aerated or not, feeding rate, feeding frequency, level of crude protein (CP), stocking weight (IBW) and harvest weight, water temperature, pH, salinity, feed conversion ratio (FCR) here defined as the ratio of total feed given / total biomass of fish harvested, dissolved oxygen (DO), survival and calculated thermal growth coefficient (TGC).

    Results
    Using linear regression we found significant effects of strains (Abassa, FaST, GIFT, Imaela, Maryut and unspecified strain), culture unit, study length, IBW and feeding rate on FCR, survival and growth, calculated as TGC. The effect of strain was also significant on FCR and survival. FCR, survival and TGC increased with higher levels of dissolved oxygen (DO) and with higher levels of CP in the diet. Increased water temperature (range 21.5 to 28.5oC) favourably reduced FCR and improved survival (range 10 - 37oC). Higher salinity (range 0 to 30 ppt) reduced the survival of fish and growth (range 0 - 24ppt). Increased feeding rate improved survival and TGC while FCR was negatively affected by increased feeding rate. Increased dark photoperiod had a significant negative effect on TGC. The effect of stocking density on FCR, survival and TGC was not significant for the range of densities reported in the literature.

    Discussion
    We found that the strains Abassa, FaST, GIFT, Imaela and Maryut were better in FCR than the unspecified strain. The probable reason could be that FaST, GIFT, Abassa, Maryut and Imaela strains have been selected for growth, which may have improved FCR as well. Ridha (2006) reported FaST and GIFT strains performed significantly better than unselected strains in terms of FCR. Furthermore, the strong negative genetic correlation of close to minus one between growth and FCR (Thoa et al., 2016) reported for Nile tilapia indicates that selecting for growth improves FCR. Selection for improved growth in Atlantic salmon also resulted in better FCR (Thodesen et al., 1999). In agreement with our study, stocking density was not significant in rainbow trout (Boujard T. et al. (2002) and in Oreochromis spilurus Cruz and Ridha (1989), while in African catfish (Clarias gariepinus) FCR was found to improve significantly with increasing stocking density from 4 fish m-3 to 8 fish m-3 (Toko et al., 2007).

    In line with our result Abdel-Tawwab (2012) found fish fed with a higher CP level dealt better with stress than fish fed with a lower CP level. The effect of salinity on survival and the effect of salinity and dark photoperiod on TGC was negative and significant. The effect of salinity could be explained by high energy cost of osmoregulation (Prunet and Bornancin, 1989) which reduces available energy for growth. The negative effect of dark photoperiod could be explained by the fact that tilapias are diurnal feeders and an increased dark photoperiod could affect the feed intake negatively. We found also the effect of feeding rates was significant. Survival and TGC were improved with increased feeding rate, while the best FCR was at lowest feeding rate.

    Aquaculture farms should give emphasis to the major environmental and management factors to minimize or avoid the yield gap. This could be achieved by optimizing management and optimizing breeding programs for the environments in which commercial fish will perform, especially if some variables are beyond management control and subject to genotype by environment interaction.
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