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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    Zeebaars paaigebieden en opgroeigebieden in Nederlandse wateren
    Tulp, I.Y.M. ; Hal, R. van; Damme, C.J.G. van; Smith, S.R. - \ 2016
    IMARES (Rapport / IMARES C060/16) - 35
    visserijbeheer - zeevisserij - visserijbeleid - visbestand - habitatbeheer - nederland - het kanaal (english channel) - kuitschieten - waddenzee - zeeuwse eilanden - boomkorvisserij - zeebaars - noordzee - rijpen - fishery management - marine fisheries - fishery policy - fishery resources - habitat management - netherlands - english channel - spawning - wadden sea - zeeuwse eilanden - beam trawling - sea bass - north sea - maturation
    De zeebaarspopulatie neemt sinds 2010 sterk af door een hoge visserij-inspanning en een lage aanwas van jonge zeebaars sinds 2008. Zeebaars is een langlevende soort die zich pas op latere leeftijd gaat voortplanten. Op een leeftijd van ca 4 jaar en met een lengte vanaf ca 42 cm (vrouwtjes) en 32 cm (mannetjes) beginnen ze paairijp te worden. De huidige minimum aanlandingsmaat van 42 cm heeft als gevolg dat veel vrouwtjes al gevangen worden voordat ze voor het eerst hebben kunnen paaien. Naast vangstbeperkende maatregelen wordt gezocht naar maatregelen ter bescherming van paai- en opgroeigebieden. Hiervoor is ecologische kennis nodig, die voor de Nederlandse wateren nog grotendeels ontbreekt. Aanwezigheid van paaiende volwassen zeebaarzen is direct bewijs voor een paaigebied. Het alternatief is om aan paaigebieden vast te stellen aan de hand van de verspreiding van eieren in een vroeg ontwikkelstadium. Een relatief groot aantal larven en juveniele zeebaars kan wijzen op het belang van een gebied als opgroeigebied. Aanbevelingen voor beleid Gezien de huidige staat van onze kennis, kunnen we nu geen steekhoudende aanbevelingen voor maatregelen gericht op bescherming van gebieden of habitats te geven. De evidentie voor paaigebieden is nog erg dun, de opgroeigebieden zijn wel redelijk bekend, maar over het relatieve belang van elk gebied voor de populatie is nog geen inzicht. Het is duidelijk dat overbevissing een probleem is gezien de ontwikkelingen in de aanlandingen en de afname in gemiddelde lengte bij aanlanding. Het is ook duidelijk dat de zeebaars die in Nederland gevangen wordt in ieder geval voor een groot deel afkomstig is uit het Kanaal en dat de visserij daar in het vroege voorjaar van grote invloed is op de hoeveelheid zeebaars, die later in het jaar in onze wateren terechtkomt. Op basis van de huidige gegevens en inzichten is een verdere inperking van de vangsten door zowel commerciële als recreatieve vissers in ieder geval een effectieve maatregel om de zeebaarsstand te vergroten. Of er in aanvulling daarop ook noodzaak is om gericht gebieden of habitats te beschermen of te verbeteren is met de huidige kennis en gegevens niet vast te stellen en kan alleen met aanvullend onderzoek worden vastgesteld.
    Kennisinventarisatie paaigebieden en kinderkamers Europese zeebaars (Dicentrarchus labrax)
    Smith, S.R. ; Steenbergen, J. ; Jongbloed, R.H. - \ 2015
    IMARES (Rapport / IMARES C161/15) - 35
    zeebaars - kuitschieten - vismigratie - inventarisaties - visstand - visbestand - visserijbeheer - europese unie - oosterschelde - sea bass - spawning - fish migration - inventories - fish stocks - fishery resources - fishery management - european union - eastern scheldt
    North Sea mackerel egg survey in May and June 2015
    Damme, C.J.G. van - \ 2015
    IJmuiden : IMARES (Report / Centrum voor Visserijonderzoek (CVO) 15.010) - 39
    makrelen - visseneieren - kuitschieten - distributie - visbestand - noordzee - mackerels - fish eggs - spawning - distribution - fishery resources - north sea
    After technical problems prevented the North Sea mackerel egg survey to be carried out in 2014, a successful survey was carried out in May-June 2015. The survey was carried out on board ‘RV Tridens’. The expected mackerel spawning area was covered in each of four periods in east-west transects, separated by 1 degree. In total 260 valid plankton hauls with a Gulf VII plankton sampler were performed, as well as 3 fish hauls and 4 sets of flowmeter calibrations hauls.
    Feasibility study combining North Sea and Atlantic mackerel egg surveys
    Damme, C.J.G. van; Thorsen, A. ; Brunel, T.P.A. ; Nash, R.D.M. - \ 2015
    IJmuiden : IMARES (Report / IMARES Wageningen UR C124/15) - 23
    scomber scombrus - makrelen - kuitschieten - visseneieren - visserij - noordzee - scomber scombrus - mackerels - spawning - fish eggs - fisheries - north sea
    Mackerel Scomber scombrus is a widely distributed species with a high economic and ecological importance. The North East Atlantic mackerel comprises three different spawning components. The Spawning Stock Biomass (SSB) index from the mackerel egg surveys is used as a fisheries independent tuning index for the mackerel assessment. The North Sea mackerel triennial egg survey is carried out in the year after the egg survey of the Western and Southern spawning components. Due to this time lag currently the North Sea egg survey SSB index is not used directly in the mackerel assessment. However, the egg survey is the only available information on the mackerel spawning component in the North Sea. Can the North Sea mackerel egg survey index be incorporated in the mackerel assessment and what is the impact of the incorporation of this index? Could the North Sea and Atlantic egg surveys be carried out in the same sampling year?
    Mackerel winter spawning surveys 2014 - 2015 December survey
    Damme, C.J.G. van; O'Hea, B. - \ 2015
    IJmuiden : IMARES (Report / IMARES Wageningen UR C043/15) - 12
    scomber scombrus - makrelen - kuitschieten - voortplanting - visbestand - pelagische visserij - mariene ecologie - monitoring - scomber scombrus - mackerels - spawning - reproduction - fishery resources - pelagic fishery - marine ecology - monitoring
    In recent years the western Atlantic mackerel stock has expanded, resulting in an earlier start of spawning and earlier occurrence of the mackerel peak of spawning. In 2014 and 2015, mackerel winter spawning surveys have been conducted to determine the start date of mackerel spawning in the western area. During the surveys both plankton sampling and trawl hauls are carried out. This report contains the results of the December 2014 survey, carried out on board the Nida.
    Mackerel winter spawning surveys 2014 - 2015 January survey: Survey report
    Damme, C.J.G. van; Holst, G. - \ 2015
    IJmuiden : IMARES (Report / IMARES Wageningen UR C014/15) - 12
    scomber scombrus - makrelen - kuitschieten - voortplanting - visbestand - pelagische visserij - mariene ecologie - monitoring - scomber scombrus - mackerels - spawning - reproduction - fishery resources - pelagic fishery - marine ecology - monitoring
    In recent years the western Atlantic mackerel stock has expanded, resulting in an earlier start of spawning and earlier occurrence of the mackerel peak of spawning. In 2014 and 2015, mackerel winter spawning surveys have been conducted to determine the start date of mackerel spawning in the western area. During the surveys both plankton sampling and trawl hauls are carried out. This report contains the results of the January 2015 survey, carried out on board the CETON S205.
    Atlantic mackerel and horse mackerel egg survey 2013: Dutch participation
    Damme, C.J.G. van - \ 2014
    IJmuiden : IMARES (Report / IMARES Wageningen UR C0100/14) - 35
    trachurus trachurus - makrelen - visseneieren - kuitschieten - bemonsteren - eierproductie - tellingen - visbestand - trachurus trachurus - mackerels - fish eggs - spawning - sampling - egg production - censuses - fishery resources
    In 2013 the international Atlantic mackerel and horse mackerel egg survey was performed. This year the entire spawning area was sampled by 10 institutes from 9 different countries: Faeröer Islands, Germany, Iceland, Ireland, Norway, Portugal, Scotland, Spain and The Netherlands. Sampling started in February along the Portuguese coast and continued until July west of Scotland. The Dutch institute IMARES participated in the survey in May and June on board ‘RV Tridens’. IMARES covered the area of the Northern Bay of Biscay and Southern Celtic Sea once each month.
    Don’t put all your eggs in one basket! : reproductive strategies and fecundity regulation in temperate marine teleosts
    Damme, C.J.G. van - \ 2013
    Wageningen University. Promotor(en): Adriaan Rijnsdorp, co-promotor(en): O.S. Kjesbu; Mark Dickey-Collas. - Wageningen : Wageningen UR - ISBN 9789461736253 - 183
    teleostei - zeevissen - voortplanting - voortplantingspotentieel - oöcytrijping - kuitschieten - biomassa - eierproductie - visstand - visserijbiologie - visserijbeheer - teleostei - marine fishes - reproduction - fecundity - oocyte maturation - spawning - biomass - egg production - fish stocks - fishery biology - fishery management

    In fisheries management the spawning stock biomass (SSB) is an important indicator of the status of exploited fish stocks. Knowledge on the reproductive biology is essential to estimate SSB. A large variety of reproductive strategies is found. In marine fish two extreme strategies are known, capital spawners which have a determinate fecundity (no de novo oocyte recruitment during spawning), and income spawners which have an indeterminate fecundity (de novo oocyte recruitment during spawning). In this thesis fecundity regulating mechanisms are studied in commercial fish species with contrasting life history.

    In capital spawning plaice Pleuronectes platessa and herring Clupea harengus , which spawn in autumn and/or winter, oocyte maturation starts around April when daylight length increases. Both species recruit a high number of oocytes which are down-regulated in the course of time in relation to the available energy. After the summer feeding period, when energy levels are highest, plaice shows a second recruitment phase. In herring, no difference was observed in the oocyte development between autumn and winter spawners, although winter spawners continue developing oocytes and spawn fewer but larger eggs. The income breeding horse mackerel Trachurus trachurus utilises food resources during spawning although the first batch of spawned eggs is developed on stored energy.

    Food availability, through the body condition, is the most important factor regulating fecundity. In situations where food is available during the spawning season traditional determinate spawners may switch to a pseudo-indeterminate fecundity style. In conclusion this thesis shows that fecundity type of marine fish females is not fixed at the species level but represents a plastic response to the environment through food availability and energy allocation.

    Blauwe wijting op de weg omhoog (interview met Sven Gastauer)
    Gastauer, S. - \ 2013
    Visserijnieuws (2013)22. - ISSN 1380-5061 - p. 28 - 31.
    micromestistius poutassou - visstand - kuitschieten - visserij - biomassa - fish stocks - spawning - fisheries - biomass
    Positieve berichten van het blauwe wijtingfront. Tijdens de internationale blauwewijtingsurvey on maart/april werd een sterke toename van het paaibestand vastgesteld. Wetenschapper Sven Gastauer van IMARES Wageningen UR leidde het Nederlands deel van de operatie en doet verslag.
    Zoute spiering lijkt biet te paaien in IJsselmeer: onderzoek IMARES en Universiteit van Brussel (interview met
    Tulp, I.Y.M. - \ 2013
    Visserijnieuws 33 (2013)34. - ISSN 1380-5061 - p. 2 - 2.
    osmerus - visstand - kuitschieten - waddenzee - ijsselmeer - fish stocks - spawning - wadden sea - lake ijssel
    Zoute spiering uit de Waddenzee paait nog nauwelijks in het IJsselmeer. Dat kan mede een verklaring zijn voor de achteruitgang van de IJsselmeerspiering. Dat blijkt uit onderzoek van IMARES Wageningen en de Universiteit van Brussel dat in juli 2013 werd gepubliceerd.
    Optimisation of selective breeding program for Nile tilapia (Oreochromis niloticus)
    Trong, T.Q. - \ 2013
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Hans Komen. - S.l. : s.n. - ISBN 9789461735447 - 176
    oreochromis niloticus - selectief fokken - veredelingsprogramma's - genetische parameters - voortplantingskenmerken - kuitschieten - voortplantingspotentieel - vruchtbaarheid - heritability - genotype-milieu interactie - groeitempo - dierveredeling - visteelt - aquacultuur - oreochromis niloticus - selective breeding - breeding programmes - genetic parameters - reproductive traits - spawning - fecundity - fertility - heritability - genotype environment interaction - growth rate - animal breeding - fish culture - aquaculture

    The aim of this thesis was to optimise the selective breeding program for Nile tilapia in the Mekong Delta region of Vietnam. Two breeding schemes, the “classic” BLUP scheme following the GIFT method (with pair mating) and a rotational mating scheme with own performance selection and natural group spawning, were investigated. In the latter scheme, the aim was to mimic natural spawning conditions of Nile tilapia to reduce the time for family production; however reconstruction of pedigrees using DNA markers to monitor inbreeding is required. Parental assignment using microsatellites and SNPs showed that exclusion- and likelihood-based methods are equally good for parental assignment, provided that good marker sets with high exclusion power, such as SNPs, are available and that all parents are sampled. Prolonged family production is problematic in BLUP breeding value estimation and could be a consequence of selection for harvest weight in Nile tilapia. Using a natural mating design with single males mated to multiple females in groups, 85% of the successful spawns were collected within 20 days. Genetic correlations between harvest weight and spawning success ranged from 0.48 to 0.52, provided that the mating period is limited to 20-32 days. We conclude that Nile tilapia favour mating in groups, and that selection for harvest weight in GIFT should improve spawning success of Nile tilapia. Moreover, harvest weight and body weight at spawning have favourable genetic correlations with number of eggs, relative fecundity, and number of swim-up fry, which are the desired characteristics for Nile tilapia seed production. High-input cages and low-input ponds are the dominant production systems for tilapia in the Mekong Delta. We show that selection in nucleus ponds will produce desired correlated responses in Nile tilapia grown in river-cages. Moreover, they are expected to develop a more rotund and thicker body shape at the same length compared to fish grown in ponds. In conclusion, we recommend the use of the ‘single male, multiple females’ mating as this will reduce the generation interval by 2 months, thereby increasing genetic gain by about 20%. A rotational mating scheme, with at least 4 cohorts, can be incorporated into the GIFT selection scheme to further reduce inbreeding, to estimate pond effects and to secure the breeding material. Finally, a reliable multiplier system is important to sustain the current Nile tilapia breeding program, which can provide sufficient improved fry (>50 million per year) for the whole Mekong Delta Nile tilapia production.

    North Sea mackerel egg survey: dutch participation may and June 2011
    Damme, C.J.G. van - \ 2012
    IJmuiden : IMARES (Report / IMARES Wageningen UR no. C026/12) - 32
    makrelen - distributie - monitoring - kuitschieten - visseneieren - noordzee - mackerels - distribution - monitoring - spawning - fish eggs - north sea
    Every three years an international North Sea survey is carried out by two European institutes, Institute for Marine Research (IMR) from Norway and Institute for Marine Resources and Ecosystem Studies (IMARES) from the Netherlands, to monitor the spatial and seasonal distribution of North Sea mackerel. In 2011 the North Sea mackerel egg survey was performed. The entire spawning area was sampled by IMR, Norway and IMARES, The Netherlands. The whole spawning area was sampled three times. IMARES covered the complete sampling area in the first period, in the second period IMR covered the northern part and IMARES the southern part of the spawning area. The third period the whole spawning area was covered by IMR. In total 190 ichthyoplankton samples were taken with a Gulf VII plankton torpedo with a Seabird CTD mounted on top. Additionally, adult fish samples for the estimation of fecundity and atresia were taken using a pelagic trawl. The survey was successful and IMARES managed to sample all but 3 of the planned stations. Numbers of mackerel eggs found in the samples were comparable to 2008. Total mackerel egg production in 2011 was 116*1012 and Spawning Stock Biomass (SSB) was estimated at 165*103 tons, which is slightly higher compared to 2008. Highest egg production was found in the first sampling week and it is possible that the beginning of mackerel spawning is missed.
    Hatchery manual for broodstock management and larval production of tubrot (Psetta maxima)
    Rurangwa, E. ; Poelman, M. - \ 2011
    Yerseke : IMARES (Report / IMARES Wageningen UR C150/11) - 52
    tarbot - larven - broeddieren - bedrijfsvoering - visproductie - dierhouderij - voortplanting - broedinstallaties - kuitschieten - visziekten - visteelt - aquacultuur - turbot - larvae - broodstock - management - fish production - animal husbandry - reproduction - hatcheries - spawning - fish diseases - fish culture - aquaculture
    This hatchery manual is intended to provide detailed information from available published work and grey literature on turbot broodstock management and larval production. In reviewing larviculture techniques for turbot, it is notable that the major initial zoo technical advances were made in the 1980s. Subsequent refinements have been industry-led and are subject to commercial confidentiality. Some actors in the sector that have been approached either did not provide requested information or denied access to their sources of information. This manuscript therefore considers those aspects of commercial rearing techniques that are in the public domain, together with the applied scientific literature and information collected from different experts. With the aim to cover all aspects related to the production of turbot juveniles in Dutch farms from egg to fish of 10-15 g, the manual describes in details different steps. These have been grouped around the broodstock management, the hatchery/nursery period, the on growing and the grow out periods. A list of common diseases in turbot has been added at the end. The manual provides a link to the most update information available on live prey production and enrichment.
    Shorlist Masterplan Wind. Evaluation of the sampling grid of the year-round ichthyoplankton survey
    Bolle, L.J. ; Beek, J.K.L. van - \ 2011
    IJmuiden : IMARES (Report / IMARES Wageningen UR C026/11) - 34
    zoöplankton - kuitschieten - bemonsteren - monitoring - methodologie - visseneieren - larven - vissen - het kanaal (english channel) - noordzee - zooplankton - spawning - sampling - monitoring - methodology - fish eggs - larvae - fishes - english channel - north sea
    Within the research programme 'Shortlist Masterplan Wind' a year-round ichthyoplankton survey is being carried out. The sampling area is based on known spawning concentrations and prevailing currents.
    Spawning closures: ecological and economic trade-offs in management of mixed demersal flatfish fisheries in the North Sea
    Rijnsdorp, A.D. ; Overzee, H.M.J. van; Poos, J.J. - \ 2011
    IJmuiden : IMARES (Report / IMARES Wageningen UR C067/11) - 45
    visserijbeheer - vis vangen - demersale vissen - periode van kuitschieten - kuitschieten - duurzaamheid (sustainability) - effecten - fishery management - fishing - demersal fishes - spawning season - spawning - sustainability - effects
    The contribution of spawning closures to sustainable management of North Sea flatfish fisheries is explored using a spatial and temporal explicit model of four target species (sole, plaice, turbot and brill) and two bycatch species (cod, rays). Seasonal patterns in fishing effort and partial fishing mortality rates per day at sea by age group and area are estimated to quantify the effect of different spawning closure scenarios for sole and plaice on the exploitation pattern (F-at-age).
    Atlantic mackerel and horse mackerel egg survey: Dutch participation May and June 2010
    Damme, C.J.G. van; Bakker, C. - \ 2010
    IJmuiden : IMARES (Report / IMARES Wageningen UR no. C078/10) - 33
    visserij - visserijbeheer - trachurus trachurus - monitoring - visseneieren - kuitschieten - periode van kuitschieten - voortplantingsgedrag - fisheries - fishery management - trachurus trachurus - monitoring - fish eggs - spawning - spawning season - reproductive behaviour
    Every three years an international Atlantic survey is carried out by different European institutes to monitor the spatial and seasonal distribution of Atlantic mackerel and horse mackerel. During this survey mackerel and horse mackerel eggs are sampled using a plankton torpedo or bongo nets. The survey covers the whole spawning area and season. It starts along the Portuguese coast in February and continues until July when the waters west of Scotland are sampled. The mackerel and horse mackerel egg survey is coordinated by the ICES working group for mackerel and horse mackerel egg surveys (WGMEGS). England and France started the egg survey in the western area in 1977. The Netherlands participates since 1983. Nowadays participating countries and sampling area have expanded. In 2010 the following countries participated in this survey: Faeröer Islands, Germany, Iceland, Ireland, Norway, Portugal, Scotland, Spain and The Netherlands.
    Effects of fishing during the spawning period: implications for management
    Rijnsdorp, A.D. ; Overzee, H.M.J. van - \ 2010
    IJmuiden : IMARES (Report / IMARES Wageningen UR no. C077/10) - 33
    visserij - visserijbeheer - duurzame ontwikkeling - kuitschieten - periode van kuitschieten - visserij-ecologie - visfauna - visserijbiologie - fisheries - fishery management - sustainable development - spawning - spawning season - fisheries ecology - fish fauna - fishery biology
    Avoidance of fishing during the spawning season has been proposed as a contribution to achieving sustainable exploitation. Here we review the biological effects of fishing during the spawning period and explore their implication on sustainable management. A distinction will be made between direct mortality and indirect effects. The latter will review how fishery disturbance will affect the physiology and behaviour. Based on the results, a classification scheme is presented of the vulnerability for fisheries during the spawning period. Finally the implications for the population dynamics and fisheries management are discussed.
    Effecten van de visserij gedurende het voortplantingsseizoen op het duurzaam beheer van visbestanden: een uitgebreide Nederlandse samenvatting
    Overzee, H.M.J. van; Rijnsdorp, A.D. - \ 2010
    IJmuiden : IMARES (Rapport / IMARES Wageningen UR 076/10) - 21
    kuitschieten - periode van kuitschieten - visserij - voortplantingsvermogen - gedrag - visserij-ecologie - spawning - spawning season - fisheries - reproductive performance - behaviour - fisheries ecology
    In opdracht van Stichting Vis & Seizoen heeft IMARES een uitgebreide literatuurstudie uitgevoerd naar de mogelijke effecten van de visserij tijdens het voortplantingsseizoen. Dit rapport geeft een uitgebreide Nederlandse samenvatting van het Engelstalige rapport “Effects of fisheries during the spawning season: implications for management”.
    Use of genomic information in mass-spawning fish
    Massault, C. - \ 2010
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Henk Bovenhuis; D.J. de Koning. - [S.l. : S.n. - ISBN 9789085856887 - 172
    loci voor kwantitatief kenmerk - aquacultuur - dicentrarchus labrax - pagrus aurata - kuitschieten - morfometrie - stressreactie - pasteurellose - selectief fokken - genexpressieanalyse - diergenetica - quantitative trait loci - aquaculture - dicentrarchus labrax - pagrus aurata - spawning - morphometrics - stress response - pasteurellosis - selective breeding - genomics - animal genetics
    This thesis uses the current genetic and genomic resources to permit genetic improvement of stress response in European sea bass and disease resistance in gilthead sea bream, two traits of economical importance. One way to integrate such genetic knowledge into breeding programmes, is to detect for quantitative trait loci (QTLs), which are regions of the genome influencing a specific trait. The first step was to design successful experiments to detect QTLs in aquaculture species. The next part of the thesis focuses on QTL mapping in natural mating mass-spawning species, which have complex population structure (variable family sizes). Finally, the possibilities of using genomic selection for mass-spawning species, where natural mating is used, were investigated.
    Levels of inbreeding in group mating captive broodstock populations of Common sole, (Solea solea), inferred from parental relatedness and contribution
    Blonk, R.J.W. ; Komen, J. ; Kamstra, A. ; Crooijmans, R.P.M.A. ; Arendonk, J.A.M. van - \ 2009
    Aquaculture 289 (2009)1-2. - ISSN 0044-8486 - p. 26 - 31.
    vissen - tong (vis) - voortplanting - natuurlijke paring - populatiegenetica - nageslacht - inteelt - kuitschieten - afstamming - heterozygotie - genetische diversiteit - genetische bronnen - fishes - dover soles - reproduction - natural mating - population genetics - progeny - inbreeding - spawning - parentage - heterozygosity - genetic diversity - genetic resources - cod gadus-morhua - fish breeding programs - dover sole - spawning aggregations - scophthalmus-maximus - reproductive success - genetic-variation - mass selection - dna markers - senegalensis
    In this paper, we estimate levels of inbreeding with parental relatedness and contribution inferred from microsatellites in groups of Common sole that reproduce by natural mating. We present results on spawning patterns during one entire reproductive season of wild Common sole, Solea solea, kept in two broodstock groups (28 animals in broodstock A; 20 animals in broodstock B) under semi-natural conditions. Batches of eggs were collected daily and incubated separately. First, we performed a parentage analysis on parents and samples of 24 newly hatched larvae from all batches, using 10 polymorphic microsatellite markers. As expected, contribution of parents to offspring was highly skewed. In both broodstocks, five or less parental pairs produced more than half of the total progeny. Natural spawning and unequal contributions of parents to offspring resulted in significant deviations from Hardy–Weinberg equilibria. Furthermore, few alleles were lost and levels of heterozygosity in offspring population increased. Next, we calculated relatedness between parents that mated successfully based on estimates of molecular similarity. Mean coefficients of coancestry in offspring were determined using parental relatedness and contributions. Levels of coancestry in progeny were substantially high. These results show that due to different parental contributions, natural mating in groups can result in significant inbreeding in future generations despite of limited loss of alleles and high levels of heterozygosity in first generation progeny. This shows that using loss of alleles and levels of heterozygosity alone can be misleading for estimation of genetic diversity.
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