741 research outputs found
WESSELS, Johannes Inventory of documents
No full textCOVERAGE 1961-1980; 6 Files; 0,20 MetrePrivate papers of J. Wessels, Managing Director Blomanda Housing Scheme; Author of several publication
Enhancement of survival and growth in crowded groups: the road towards an intensive production of the noble crayfish Astacus astacus L. in indoor recirculation systems
No full textHigh mortality from cannibalism in crowded cultures of the noble crayfish (Astacus astacus L.) was the reason why the efforts for an intensive production of this species in the 1980s were largely stopped. In the present study, 14- to 15-month-old juveniles of A.astacus were cultured in tanks of an indoor recirculation system under constant summer conditions' (19 degrees C, LD 16:8) from early August to late January. The animals continued to moult and grow, indicating that the absence of these processes in the field from autumn to late spring does not involve any endogenous programming. The experimental design (suitable hiding places in excess, highly diversified diet, and special daily and lunar light regimes) ensured high survival (>90%) and growth rates which were largely independent of stocking rate (1560individuals per m2). Moulting occurred during daytime which allowed freshly moulted animals to escape from cannibalistic attacks of their nocturnal conspecifics. There is a first indication that an artificial moonlight cycle can synchronize moulting events (maximum around new moon'), in this way contributing to a further decrease in mortality. The results encourage a resumption of efforts for an intensive production of A.astacus in indoor recirculation systems
Tilapia sex determination: Where temperature and genetics meet
No full textThis review deals with the complex sex determining system of Nile tilapia, Oreochromis niloticus, governed by the interactions between a genetic determination and the influence of temperature, shown in both domestic and wild populations. Naturally sex reversed individuals are strongly suggested in two wild populations. This can be due to the masculinising temperatures which some fry encounter during their sex differentiation period when they colonise shallow waters, and/or to the influence of minor genetic factors. Differences regarding a) thermal responsiveness of sex ratios between and within Nile tilapia populations, b) maternal and paternal effects on temperature dependent sex ratios and c) nearly identical results in offspring of repeated matings, demonstrate that thermosensitivity is under genetic control. Selection experiments to increase the thermosensitivity revealed high responses in the high and low sensitive lines. The high-line showed ~ 90% males after 2 generations of selection whereas the weakly sensitive line had 54% males. This is the first evidence that a surplus of males in temperature treated groups can be selected as a quantitative trait. Expression profiles of several genes (Cyp19a, Foxl2, Amh, Sox9a,b) from the gonad and brain were analysed to define temperature action on the sex determining/differentiating cascade in tilapia. The coexistence of GSD and TSD is discussed
An Interview with Tom Wessels
No full textAssociate Editor of Taproot, Patrick Pryor, interviewed Tom Wessels, author of two books, Reading the Forested Landscape: A Natural History of New England and The Granite Landscape: A Natural History of America\u27s Mountain Domes, from Acadia to Yosemite. Tom is also Director of the Masters Degree Program in Environmental Biology, at Antioch New England Graduate School. At Antioch he helped develop the Environmental Biology program that trains field ecologists to conduct research for non-profit, environmental organizations. He is also an Ecological Consultant for The Rain Forest Alliance\u27s Smart Wood Program where he has developed green certification assessment· guidelines for timber operations in the Northeast and educates foresters about management activities that enhance diversity at the landscape level
Does Genetic Background of Rainbow Trout Impact Growth and Feed Utilisation following Fishmeal Substitution by Partly Defatted Insect Meal (Hermetia illucens) or Microalgae Powder (Arthrospira platensis)?
No full textA growth trial was carried out to evaluate differences in feed utilisation and growth performance in response to substitution of fishmeal (FM) by either partly defatted insect meal or microalgae powder in different strains of rainbow trout. Three iso-nitrogenous and iso-energetic diets were fed to 495 juvenile rainbow trout with initial weight of 150 ± 37 g. Whereas, the control diet included 20% FM, the two experimental diets were free of FM. Instead of that, an equal amount of spray-dried Spirulina powder (SP) or partly defatted Hermetia meal (HM) was applied as alternative protein source. Feed utilisation and growth response were investigated in a commercial breed (TL) and three local strains (HK3, HK7, and HK8) over a period of 56 days using three replicates per diet. Diets were fed relative to fish body weight throughout at a constant rate of 1.0%. Although growth was comparable among diets, growth and feed utilisation differed between breeds. The strain TL tended to express the highest specific growth rate, however, associated with lower feed conversion. Protein utilisation was superior in local strains irrespective of diet, most pronounced between strains HK7 and TL. Due to large differences in initial body weights, compensatory growth might have affected the study’s outcome. Both alternative protein sources showed to be adequate to fully replace FM in diets for rainbow trout. Improved adaption to diets including high levels of HM or SP might be achieved by selective breeding
Total Replacement of Fishmeal by Spirulina (Arthrospira platensis) and Its Effect on Growth Performance and Product Quality of African Catfish (Clarias gariepinus)
No full textMicroalgae are increasingly being studied to replace fishmeal in aquafeed production. Low level Spirulina supplementation to various fish species has been widely investigated, demonstrating enhanced growth and better product quality. In order to evaluate the effects of a full fishmeal replacement with Spirulina (Arthrospira platensis) on growth and product quality in African catfish (Clarias gariepinus), two isoenergetic diets were formulated and fed for ten weeks to 120 fish with an average initial weight of 50 ± 3 g. Full supplementation of Spirulina resulted in reduced growth (p < 0.001) whereas feed conversion ratio was on par (p > 0.05). Furthermore, Spirulina-fed fish showed a more intense yellow coloration in skin, and raw and cooked fillet (p < 0.001). The analysis of fatty acids revealed higher proportions of C16:0 (p < 0.001) and C18:2n6 (p < 0.05) in fish fed the Spirulina-diet while C24:0 (p < 0.01) and C20:5n3 (p < 0.001) were found to be higher in the control group. Even though no statistically significant differences in the overall SFA, MUFA and PUFA were detected, a slight increase of the n6/n3 ratio was observed in the Spirulina-fed fish. Without further optimization of the feed ration, a complete fishmeal replacement with Spirulina can lead to economic losses. It remains to be studied whether the observed changes in product quality affect consumer acceptance
Germline Development of Genetically Female Nile Tilapia (<b><i>Oreochromis niloticus</i></b>) Reared under Different Temperature Regimes
No full textIn teleosts, elevated temperature during embryogenesis can act on germline cell development, which in turn plays a role for sexual fate. In Nile tilapia, a species with high-temperature-induced masculinization, little is known about the effects of increased temperature on gonadal development in non-masculinized females. The aim of the present work was to investigate persistent effects on the germline of genetically female (XX) Nile tilapia reared at normal (28°C) or elevated temperature (36°C) during the critical time of gonadal sex differentiation at 10 to 20 days post fertilization. Non-sex-reversed females were compared to control females to determine persistent effects of temperature on subsequent ovarian development using histological approaches. Germline stem cells were identified using the germline marker Vasa in combination with the proliferation marker PCNA. Vasa- and PCNA-positive germline stem cells were found in ovaries of both high-temperature-treated and control females. In both groups, ovarian germline stem cells were located at the germinal epithelium of the ovigerous lamellae. Although no detrimental effects of high temperature on gonadal development in female Nile tilapia were observed, implications on the reproductive fitness caused by elevated temperature need to be investigated in greater depth.</jats:p
Stocking Density and Photoperiod Manipulation in Relation to Estradiol Profile to Enhance Spawning Activity in Female Nile Tilapia
No full textThis study investigated the effects of stocking density and photoperiod manipulation in relation to plasma estradiol-17β (E2) profile to enhance spawning activity in female Nile tilapia using F1 clonal crosses. The fish were divided into experimental and control groups and subjected to a combination of stocking density and photoperiod treatments (40 kg/m3; 6L:18 D, 40 kg/m3; 12 L:12 D and transferred into single compartments at 12 L:12 D; 14 kg/m3; 12L:12D, respectively). Blood samples were taken by caudal puncture from both experimental and control fish for estradiol profile analysis. Results showed that experimental fish exhibited significantly higher number of spawns per day, total and relative fecundity, hatching and swim-up rates (P<0.05). Regression analyses revealed a significant positive relationship between fish size (body weight), and total and relative fecundity (P<0.001). It was also revealed that E2 levels demonstrated a pattern based on completed reproductive cycle in the experimental fish. The study therefore established that a combination of stocking density and photoperiod treatments can be adopted to manipulate the timing of spawning activity in female Nile tilapia without having adverse effect on other reproductive parameters such as egg qualities and fecundity. Findings further suggested that the effects of exogenous factors on manipulation of spawning activities of female Nile tilapia may be achieved as a result of hormonal changes including E2 levels
ddRADseq reveals determinants for temperature-dependent sex reversal in Nile tilapia on LG23
No full textAbstract Background In Nile tilapia sex determination is governed by a male heterogametic system XX/XY either on LG1 or LG23. The latter carries a Y-specific duplicate of the amh gene, which is a testis-determining factor. Allelic variants in the amh gene demonstrated to be major triggers for autosomal and temperature-dependent sex reversal. Further, QTL on LG23 and LG20 show a temperature-responsiveness with influence on the phenotypic sex relative to the sex chromosomes. Here we present a ddRADseq based approach to identify genomic regions that show unusual large differentiation in terms of fixation index (FST) between temperature-treated pseudomales and non-masculinized females using a comparative genome-scan. Genome-wide associations were identified for the temperature-dependent sex using a genetically all-female population devoid of amh-ΔY. Results Twenty-two thousand three hundred ninety-two SNPs were interrogated for the comparison of temperature-treated pseudomales and females, which revealed the largest differentiation on LG23. Outlier FST-values (0.35–0.44) were determined for six SNPs in the genomic interval (9,190,077–11,065,693) harbouring the amh gene (9,602,693–9,605,808), exceeding the genome-wide low FST of 0.013. Association analysis with a set of 9104 selected SNPs confirmed that the same genomic region on LG23 exerts a significant effect on the temperature-dependent sex. Conclusions This study highlights the role of LG23 in sex determination, harbouring major determinants for temperature-dependent sex reversal in Nile tilapia. Furthermore FST outlier detection proves a powerful tool for detection of sex-determining regions in fish genomes
Maternal education potentially moderates the MAOA uVNTR effects on externalizing behavior in Black South African children
No full textInteractions between the MAOA uVNTR and rearing environment are suggested to influence the developmental manifestations of childhood internalizing and externalizing behavior. However, few studies in the MAOA literature have included continental African children, or focused on non-clinical samples. We explored the main and interactive effects of the MAOA uVNTR (high and low activity alleles) in Black South African male (n = 478) and female (n = 540) children who were part of the longitudinal Birth to Twenty Plus cohort. Historical data on birth weight, gestational age at delivery, socioeconomic status, and maternal education were combined with genotypic information and analyzed using regression modeling. We found no significant main effects for the MAOA uVNTR on childhood behavior in either sex. A significant interaction (p = .04) was identified between MAOA and maternal education, suggesting that externalizing behavior in boys carrying a low activity MAOA allele varied in direct proportion to the education levels of their mothers. However, the model fit failed to reach significance, possibly due to our inclusion of only non-clinical pre-pubertal males. No significant interactions were detected for female children. Our findings lend tentative credibility to the Environmental Sensitivity metaframework, which suggests that MAOA is an important plasticity factor in childhood development
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