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Th.--Sci. nat.--Paris 6, 1978.

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During the last decades marine aquaculture has steadily expanded and diversified to include a wider range of commercial species. Despite the intense effort towards understanding the biological requirements of farmed species, several issues remain to be addressed. Mariculture success is restricted by a number of production bottlenecks including limited seed supply, caused mainly through a combination of compromised productivity in broodstock paired with high mortalities during the early life stages. Productivity and survival success is often dependent on the successful recreation of natural environmental conditions. While in a commercial setting a concerted effort is generally made to simulate key environmental stimuli there remains a lack of understanding of the significance of many potential signals. The overarching aim of this thesis was to investigate the effects of some of the overlooked environmental stimuli on fish performance in enclosed facilities and where possible relate this to the natural setting from which the species have been removed. The studies contained in this text are focused on the effects of anthropogenic noise, light spectral composition and substrate on the performance of broodstock and juvenile development of two valuable commercial marine species Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus). The aim of Chapter 3 was to test if artificial sound can act as a stressor in Atlantic cod and thereafter to examine if chronic sound disturbances can compromise broodstock spawning performance in land-based facilities. Results showed that anthropogenic noises in a land-based marine farm are within the auditory thresholds of cod and other fish species. Juvenile cod exposed to 10 min of artificial noise (100-1,000 Hz) from 10 to 20 dB 1 re µPa above background sound levels presented a typical acute stress response with a 4 fold elevation of plasma cortisol levels within 20 min, with a return to basal levels after 40 min, while the intensity of the stress response (in terms of amplitude and return to normal levels) appeared to be correlated to the noise level applied. When a similar artificial noise of 35 dB 1 re µPa above background sound level was applied to a broodstock population daily on a random schedule during the spawning season, it significantly impacted on reproductive performances in comparison to a control undisturbed population with notably a reduction in fertilisation rate that correlated with increased egg cortisol contents. Overall, these studies confirmed, for the first time, that artificial noise mimicking anthropogenic sounds generated in marine land-based facilities trigger a typical acute stress response if a similar sound exposure is then applied in a chronic manner it resulted in reduced broodstock spawning performances. Overall this work provides novel evidence on the potential of anthropogenic noise to act as stressor in fish. The possible implications for both captive and wild stock are discussed. In chapter 4 the effects of light spectrum and tank background colour on Atlantic cod and turbot larval performance from hatch until the end of metamorphosis were investigated. In both species larvae exposed to shorter wavelengths (blue and green spectrums) showed significantly enhanced growth in terms of standard length, myotome height, eye diameter and condition factor in comparison to larvae exposed to longer wavelengths (red). Larvae performances in the colour background experiment differed between species. Atlantic cod larvae reared in a red tank background displayed the best growth and survival, while larvae in blue tank background had a significant positive effect on final survival rate. In contrast, turbot larvae survival rates were the highest in the red tank background colour with the lowest growth parameters, while larvae in the blue tank background displayed the best growth. In both species, white tank background colour resulted in the lowest final survival rate. These results highlight the biological relevance of light spectrum and background colour in marine larvae performance and survival, demonstrating the importance of considering the light composition of the light units used in the hatcheries for larval rearing. Subsequently in chapter 5 the effects of light spectrum in juvenile turbot growth, appetite, stress response and skin pigmentation were investigated. Two sets of experiments were performed with post-metamorphosed (1 g) and on-growing (100 g) turbot. Results demonstrated that short wavelength treatments had a significant positive effect on growth parameters (total length and wet weight), food intake and feeding response. Light treatments caused a positive correlation between plasma glucose and cortisol levels with significant differences between the short and long wavelength treatments. Skin pigmentation was affected by the light treatments, showing a relationship between wavelength and brightness (negative) and darkness (positive). Blue light treatment resulted in brighter and lighter skin colouration, while red light had the opposite effect: darkening of the skin. Overall these results confirm that turbot juveniles performance is enhanced by exposing them to a similar photic environment than the one from the natural ecological niche. Light spectrum intervenes in skin pigmentation and the possible mechanisms behind the variations are discussed. In general chapter 5 provides background knowledge of the possible implications of light spectrum in fish juveniles performance and possible commercial applications. The final two experimental chapters turned focus back on the optimisation of broodstock environmental management and subsequent effects on their productivity. In Chapter 6 the importance of crepuscular light simulation was investigated in Atlantic cod broodstock spawning performance. No significant impact could be observed in terms of egg production and quality in association with dawn/dusk simulation compared to abrupt lights on/off. This suggests, at least for Atlantic cod, that crepuscular light simulation is not a key factor affecting spawning performance during the spawning window. The possible implications of twilight on gamete quality prior ovulation are discussed. In Chapter 7 the effect of a “breeding nest” containing a substrate (i.e. sand) in turbot broodstock spawning performance was investigated. Behavioural observation recorded active occupancy of the nests with the suggestion of social structuring as specific individuals (females) occupied the nest preferentially. However no fertilised, naturally released eggs were collected from the overflow during the spawning seasons. This would suggest that the presence of a nest is not enough to induce natural spawning behaviour in turbot in itself however the elective occupancy suggests that nests and/or their substrate was a physical enrichment that was valued by the fish which should be explored further. Overall the studies contained in this thesis highlight further the importance of considering noise and light as crucial environmental factors in marine aquaculture. Results from the different chapters offer a possible application within the enclosed facilities that might contribute to the success of the industry. Present findings contribute towards the understanding of the effects of environmental signals in fish and provide further insight to guide further lines of research on the involvement of light spectrum on fish physiology.

Piggvarens (Scophthalmus maximus) val av habitat i Östersjön har modellerats utifrån provfiskedata och miljövariabler. Vid totalt 435 stationer i Östersjön har data samlats in i form av provfiske, CTD-mätningar (konduktivitet, temperatur och djup) och videofilmer. Genom att analysera videofilmerna från havsbotten i Östersjön har den klassificerats efter fyra olika förklaringsvariabler: täckningsgrad mjukbotten, strukturbildande växter, övriga alger och täckningsgrad blåmusslor. Ytterligare sex förklaringsvariabler har samlats in från mätningar och befintliga kartor: bottensalinitet, bottentemperatur, djup, siktdjup, vågexponering och bottenlutning. Dessa tio förklaringsvariabler har använts i tio olika enskilda statistiska modelleringsmetoder med förekomst/icke-förekomst av piggvar som responsvariabel. Nio av tio modeller visade på bra resultat (AUC > 0,7) där CTA (Classification Tree Analysis) och GBM (Global Boosting Model) hade bäst resultat (AUC > 0,9). Genom att kombinera modeller med bra resultat på olika sätt skapades sex ensemblemodeller för att minska varje enskild modells svagheter. Ensemblemodellerna visade tydligt fördelarna med denna typ av modellering då de gav ett mycket bra resultat (AUC > 0,949). Den sämsta ensemblemodellen var markant bättre än den bästa enskilda modellen. Resultaten från modellerna visar att största sannolikheten för piggvarsförekomst i Östersjön är vid grunt (< 20 meter) och varmt (> 10 oC) vatten med hög vågexponering (> 30 000 m²/s). Dessa tre variabler var de med högst betydelse för modellerna. Täckningsgrad mjukbotten och de två växtlighetsvariablerna från videoanalyserna var de tre variabler som hade lägst påverkan på piggvarens val av habitat. Med en högre kvalitet på videofilmerna hade de variablerna kunnat klassificeras i mer specifika grupper vilket eventuellt gett ett annat resultat. Generellt visade modellerna att denna typ av habitatmodellering med provfiske och miljödata både är möjlig att utföra. / The turbots’ (Scophthalmus maximus) selection of habitat in the Baltic Sea has been modeled on the basis of fish survey data and environmental variables. At a total of 435 stations in the Baltic Sea, data was collected in the form of fish survey data, CTD (Conductivity, Temperature and Depth) measurements and videos. By analyzing the videos from the seabed of the Baltic Sea, four different explanatory variables have been classified: coverage of soft bottom, structure-forming plants, other algae and coverage of mussels. Another six explanatory variables have been collected from measurements and existing rasters: salinity, temperature, depth, water transparency, wave exposure and the bottom slope. These ten explanatory variables have been used in ten different species distribution modeling methods with the presence/absence of turbot as a response variable. Nine out of ten models showed good results (AUC > 0.7) where the CTA (Classification Tree Analysis) and GBM (Global Boosting Model) performed the best (AUC > 0.9). By combining the models with good performance in six different ensemble models each individual models’ weaknesses were decreased. The ensemble models clearly showed strength as they gave a very good performance (AUC > 0.94). The worst ensemble model was significantly better than the best individual model. The results of the models show that the largest probability of occurrence of turbot in the Baltic Sea is in shallow (< 20 m) and warm (> 10 ° C) water with high wave exposure (> 30,000 m²/s). These three variables were those with the highest significance for the models. Coverage of soft bottom and the two vegetation variables, from the video analyzes, had the lowest impact on the turbots’ choice of habitat. A higher quality of the videos would have made it possible to classify these variables in more specific groups which might have given a different result. Generally, the models showed that this type of modeling of habitat is possible to perform with fish survey and environmental monitoring data and generates useful results.

It has been shown that fish of both marine and limnetic origin display increased growth at intermediate salinities. Furthermore, it has been shown that fish in the brackish water Baltic Sea are smaller compared to their conspecifics in the Atlantic, where salinities are higher. Also, it has been suggested that fish produce more eggs at the edges of their distribution range as a response to inferior environmental conditions. In this study, I investigated if there is a trade-off in energy investment between somatic and gonad growth in relation to salinity. To do this, I performed a growth experiment and a literature review. In the growth experiment, juvenile turbot were reared in salinities of 6, 10.5, 15 and 30 ‰. I found that turbot juveniles from Gotland grew equally well in all salinities investigated. In the literature review, data from the Baltic Sea was tested against data from the North and Black Seas. Data of turbot total energy investment (somatic and gonad growth) was analyzed. I found that energy content at age differed significantly between the populations investigated with lower energy content for the Baltic Sea populations. Also, growth rate in relation to energy content (size) was analyzed for the different populations, but no difference for growth rate in relation to energy content occurred. The result of the analysis of growth rate indicates that the change in allocated energy is the same, regardless of population, and thus that fish from the Baltic Sea display growth rates similar to those of other populations. It was also established that energy investment in gonads increased along with decreasing salinities. The smaller size of turbot in the Baltic Sea is therefore probably the result of a difference in size at maturity, possibly because less energy is allocated to somatic growth and more energy to start producing eggs. It is probably also the consequence of that the Baltic Sea turbot, post sexual maturity, continue to invest more energy in egg production.