Towards an effective improvement of fish health and welfare in aquaculture with standards for protocols for both the evaluation of mycotoxins and the on-farm assessment of fish welfare

Applied research in fish health and welfare misses methodological standards in certain areas and, hence, reasonable standardisation can assist effective research and facilitate improvements of fish health and welfare in aquaculture. This thesis reveals that this process of standardisation requires profound understanding of the system at hand in order to balance advantages and drawbacks of standards. By testing and developing standards for protocols this thesis contributes to improvements in fish health and welfare in the promising food production sector of aquaculture. Standards bring continuity across space and time, yet they adapt and evolve and hence standardisation is an ongoing process. In applied research, where theoretical standardisation directly encounters practical complexity, applicability may force compromises on ideal standards that render standardisation an act of balance and reasoning. Especially in young fields of research and industry, such as aquaculture, the procedure of standardisation therefore must be preceded by the question about advantages and disadvantages of standards. Aquaculture faces challenges like digitalisation, biosecurity and sustainability as well as increasing expectations regarding the production of environmentally sustainable food with an animal-friendly husbandry. Yet fish farming falls short of a profound understanding of the needs of fish and especially the ability to measure and assess fish health and welfare. The applied research in fish health and welfare is a rising and interdisciplinary field, that may benefit from better standards and improved standardisation. Fish health is fundamental for an environmentally, economically and ethically successful farming and can be measured with standardised protocols. One such protocol, the fish embryo acute toxicity test, was used in chapter 1 of this thesis to investigate the effects of mycotoxins during embryogenesis. Mycotoxicosis increasingly affects aquaculture due to contaminated fish feeds, which necessitates expedient and efficient research. The chapter shows that this standardised protocol can benefit the investigation of mycotoxicosis in fish. The chapter further reveals a considerable variability in toxicological datasets, which impedes the necessary hazard characterisation of mycotoxins. Chapter 2 therefore explores potential factors contributing to this variability and formulates specific suggestions that can contribute to an improved standardisation in hazard characterisation trials. The chapter emphasises that and how better standards can benefit hazard characterisation processes for mycotoxins in aquaculture. Fish welfare, contrary to fish health, lacks established and proven methods for a standardised assessment. As fish welfare is crucial for fish farming, chapter 3 elaborates on the development of a standardised protocol for on-farm fish welfare assessment. The model presented is comprehensive, applicable and developable and includes a user-friendly software application. This more standardised method can facilitate the harmonised on-farm evaluation of fish welfare which will promote improvements within the industry, will assist the fact-based discussion about fish welfare in aquaculture, will enable expedient advancements in regulations and will contribute towards a fish-friendly meat product

Carotenoid-based colour expression is determined early in nestling life

Carotenoid-based colours are widespread in animals and are used as signals in intra- and interspecific communication. In nestling birds, the carotenoids used for feather pigmentation may derive via three pathways: (1) via maternal transfer to egg yolk; (2) via paternal feeds early after hatching when females are mainly brooding; or (3) via feeds from both parents later in nestling life. We analysed the relative importance of the proposed carotenoid sources in a field experiment on great tit nestlings (Parus major). In a within-brood design we supplemented nestlings with carotenoids shortly after hatching, later on in the nestling life, or with a placebo. We show that the carotenoid-based colour expression of nestlings is modified maximally during the first 6 days after hatching. It reveals that the observed variation in carotenoid-based coloration is based only on mechanisms acting during a short period of time in early nestling life. The experiment further suggests that paternally derived carotenoids are the most important determinants of nestling plumage colou

Increased prenatal maternal investment reduces inbreeding depression in offspring

This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this record.Inbreeding depression refers to the reduction of fitness that results from matings between relatives. Evidence for reduced fitness in inbred individuals is widespread, but the strength of inbreeding depression varies widely both within and among taxa. Environmental conditions can mediate this variation in the strength of inbreeding depression, with environmental stress exacerbating the negative consequences of inbreeding. Parents can modify the environment experienced by offspring, and have thus the potential to mitigate the negative consequences of inbreeding. While such parental effects have recently been demonstrated during the postnatal period, the role of prenatal parental effects in influencing the expression of inbreeding depression remains unexplored. To address this gap, we performed matings between full-sibs or unrelated individuals in replicated lines of Japanese quail (Coturnix japonica) experimentally selected for high and low maternal egg provisioning. We show that in the low maternal investment lines hatching success was strongly reduced when parents were related. In the high maternal investment lines, however, this negative effect of inbreeding on hatching success was absent, demonstrating that prenatal maternal provisioning can alleviate the negative fitness consequences of inbreeding.The study was financially supported by Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (PP00P3_128386 and PP00P3_157455 to B.T.) and the Faculty of Science of the University of Zurich

Carotenoid-based nestling colouration and parental favouritism in the great tit

While elaborate carotenoid-based traits in adult birds may have evolved as honest signals of individual quality in the context of sexual selection or other social interactions, the function of carotenoid-based colours in juveniles is less well understood. We investigated the hypothesis that carotenoid-based nestling colouration has evolved in response to parental preference of intensely coloured offspring during food provisioning. In a field experiment, we manipulated nestling plumage colouration by a carotenoid-supplementation and analysed the parental food provisioning behaviour before feather appearance and at the end of the nestling stage. Carotenoids per se did not influence the nestling's begging behaviour or parental feeding decisions and we found no evidence that carotenoid-based colouration in nestling great tits has a signalling function in parent-offspring interactions. Parents did not discriminate between intensely coloured and control offspring in their food provisioning and in accordance with this finding intensely coloured nestlings were not heavier or larger at the end of the nestling stage. Alternative explanations for the evolution of carotenoid-based colours in nestling birds are discusse

A trade-off between reproductive investment and maternal cerebellum size in a precocial bird

This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this record.Natural selection favours increased investment in reproduction, yet considerable variation in parental investment is observed in natural populations. Life-history theory predicts that this variation is maintained by a trade-off between the benefits of increased reproductive investment and its associated costs for the parents. The nature of these costs of reproduction, however, remains poorly understood. The brain is an energetically highly expensive organ and increased reproductive investment may, therefore, negatively affect brain maintenance. Using artificial selection lines for high and low prenatal maternal investment in a precocial bird, the Japanese quail (Coturnix japonica), we provide experimental evidence for this hypothesis by showing that increased prenatal provisioning negatively affects the size of a particular brain region of the mother, the cerebellum. Our finding suggests that cognitive demands may constrain the evolution of parental investment, and vice versa, contributing to the maintenance of variation in reproductive behaviour in animal populations.This work was supported by the Swiss National Science Foundation (PP00P3_128386, PP00P3_157455 to B.T.) and the Georges und Antoine Claraz-Schenkung (to C.E.)

Alternative reproductive tactics in snail shell-brooding cichlids diverge in energy reserve allocation

Life history theory predicts that the amount of resources allocated to reproduction should maximize an individual's lifetime reproductive success. So far, resource allocation in reproduction has been studied mainly in females. Intraspecific variation of endogenous energy storage and utilization patterns of males has received little attention, although these patterns may vary greatly between individuals pursuing alternative reproductive tactics (ARTs). ARTs are characterized by systematic variation of behavioral, physiological, and often morphological traits among same-sex conspecifics. Some individuals may rely on previously accumulated reserves, because of limited foraging opportunities during reproduction. Others may be able to continue foraging during reproduction, thus relying on reserves to a lesser extent. We therefore predicted that, if male tactics involve such divergent limitations and trade-offs within a species, ARTs should correspondingly differ in energy reserve allocation and utilization. To test this prediction, we studied short-term and long-term reserve storage patterns of males in the shell-brooding cichlid Lamprologus callipterus. In this species, bourgeois males investing in territory defense, courtship, and guarding of broods coexist with two distinct parasitic male tactics: (1) opportunistic sneaker males attempting to fertilize eggs by releasing sperm into the shell opening when a female is spawning; and (2) specialized dwarf males attempting to enter the shell past the spawning female to fertilize eggs from inside the shell. Sneaker males differed from other male types by showing the highest amount of accumulated short-term and long-term fat stores, apparently anticipating their upcoming adoption of the nest male status. In contrast, nest males depleted previously accumulated energy reserves with increasing nest holding period, as they invest heavily into costly reproductive behaviors while not taking up any food. This conforms to a capital breeder strategy. Dwarf males did not accumulate long-term fat stores at all, which they can afford due to their small behavioral effort during reproduction and their continued feeding activity, conforming to an income breeder strategy. Our data confirm that the resource storage patterns of males pursuing ARTs can diverge substantially, which adds to our understanding of the coexistence and maintenance of alternative reproductive patterns within species

Elevational Changes in Bacterial Microbiota Structure and Diversity in an Arthropod-Disease Vector

Environmental conditions change rapidly along elevational gradients and have been found to affect community composition in macroscopic taxa, with lower diversity typically observed at higher elevations. In contrast, microbial community responses to elevation are still poorly understood. Specifically, the effects of elevation on vector-associated microbiota have not been studied to date, even though the within-vector microbial community is known to influence vector competence for a range of zoonotic pathogens. Here we characterize the structure and diversity of the bacterial microbiota in an important zoonotic disease vector, the sheep tick Ixodes ricinus, along replicated elevational gradient (630–1673 m) in the Swiss Alps. 16S rRNA sequencing of the whole within-tick bacterial microbiota of questing nymphs and adults revealed a decrease in Faith’s phylogenetic microbial alpha diversity with increasing elevation, while beta diversity analyses revealed a lower variation in microbial community composition at higher elevations. We also found a higher microbial diversity later in the season and significant differences in microbial diversity among tick life stages and sexes, with lowest microbial alpha diversity observed in adult females. No associations between tick genetic diversity and bacterial diversity were observed. Our study demonstrates systematic changes in tick bacterial microbiota diversity along elevational gradients. The observed patterns mirror diversity changes along elevational gradients typically observed in macroscopic taxa, and they highlight the key role of environmental factors in shaping within-host microbial communities in ectotherms.Peer reviewe

Bacterial microbiota composition of Ixodes ricinus ticks : the role of environmental variation, tick characteristics and microbial interactions

Peer reviewe

Long-term effects of early parasite exposure on song duration and singing strategy in great tits

Song is a sexually selected trait in many bird species and has been suggested to function as a signal of a male's health and parasite resistance. Here we present an experimental field study on the long-term effects of parasite exposure early in life on adult bird song. We exposed nestling great tits (Parus major) to ectoparasitic hen fleas (Ceratophyllus gallinae) and on their recruitment into the local breeding population assessed the response to a playback of a challenging male in their breeding territory. We show, to our knowledge for the first time in a wild bird population, that parasite exposure early in life affects bird song: song duration of males that were exposed to parasites early in life was reduced by 32% compared with males that grew up in a flea-free environment. Early parasite exposure also significantly reduced the degree of song overlap with the playback, which has been shown to correlate with social status. There was no effect of early parasite exposure on the number of different song types sung or on the latency until the males started the vocal response to the playback. These results suggest that mates or rivals can use song duration and song overlap as proxies for an individual's exposure to parasites early in life. It thereby highlights both the importance of parasites in maintaining honesty of sexually selected traits and the costs of parasitism in terms of reduced attractiveness and competitivenes

Toxicity of ochratoxin to early life stages of zebrafish (Danio rerio)

Ochratoxin A (OTA) is a known contaminant in fish feed but its effect on fish health remains rather unknown. A study was conducted to investigate the effects of different concentrations of ochratoxin on early life stages of zebrafish (Danio rerio). The tests with ochratoxin A showed a correlation between the exposure to mycotoxin and the amount of damage. The mortality rate and the incidents of embryonal damage was increased by increasing ochratoxin concentrations. The calculations resulted in a lethal concentration for 50% of the embryos (LC50) of 0.29 mg/L and a concentration at which 50% of the animals showed impairment (EC50) of 0.36 mg/L after 96 h of exposure. During the test, reduced heart rates were also observed revealing a clear dose-response relationship. The EC50 determination for this endpoint was 1.26 mg/L after 72 h of exposure. The measurement of oxidative stress was proven to be the most sensitive system to indicate OTA effects on the zebrafish embryos with an EC50 value of 0.067 mg/L after 72 h of exposure. The test validity was given because the control test with 3,4-Dichloroaniline (3,4-D) showed a LC50 value of 2.88 mg after 96 h of exposure which is comparable to the available reference values. According to the current knowledge, these experimental doses did not exceed the environmental concentrations of this ochratoxin A. However, this study raises concerns about the effects of ochratoxin on fish