Environmental management of Atlantic cod (Gadus morhua) and turbot (Scophthalamus maximus): implications of noise, light and substrate

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

Feeding behaviour and digestion physiology in larval fish – current knowledge and gaps and bottlenecks in research

Food uptake follows rules defined by feeding behaviour that determines the kind and quantity of food ingested by fish larvae as well as how live prey and food particles are detected, captured and ingested. Feeding success depends on the progressive development of anatomical characteristics and physiological functions and on the availability of suitable food items throughout larval development. The fish larval stages present eco-morpho-physiological features very different from adults and differ from one species to another. The organoleptic properties, dimensions, detectability, movements characteristics and buoyancy of food items are all crucial features that should be considered, but is often ignored, in feeding regimes. Ontogenetic changes in digestive function lead to limitations in the ability to process certain feedstuffs. There is still a lack of knowledge about the digestion and absorption of various nutrients and about the ontogeny of basic physiological mechanisms in fish larvae, including how they are affected by genetic, dietary and environmental factors. The neural and hormonal regulation of the digestive process and of appetite is critical for optimizing digestion. These processes are still poorly described in fish larvae and attempts to develop optimal feeding regimes are often still on a ‘trial and error’ basis. A holistic understanding of feeding ecology and digestive functions is important for designing diets for fish larvae and the adaptation of rearing conditions to meet requirements for the best presentation of prey and microdiets, and their optimal ingestion, digestion and absorption. More research that targets gaps in our knowledge should advance larval rearing

Sex reversal and early larval biology of farmed silver perch, Bidyanus bidyanus (Mitchell, 1838) in Western Australia

The intensive aquaculture of silver perch in Western Australia is constrained by the lack of control on the broodstock sex and a detailed biological information on the early larval stages. Five experiments were performed to study the reproductive biology of the species, the sex reversals and the feeding biology of the early life of larvae. The result showed that the domestication of the broodstock and the sex reversal are viable options with hormonal feed supplementations

Egg quality, triploidy induction and weaning of the Atlantic halibut Hippoglossus hippoglossus

The supply of juvenile Atlantic halibut, Ilippof’lossus hippoglossus, has been sporadic and until recently, has fallen short of expectations, due to difficulties associated with the hatchery phase. This thesis focuses on some specific aspects of intensive hatchery production which needed to be addressed in the areas of egg production and quality, triploidy induction and weaning. A quality assessment technique for halibut eggs, based on observations of morphological anomalies occurring during early blastomere divisions was devised. The degree of abnormality in the appearance of five features was quantified and a strong relationship between these characteristics and hatch rate of eggs incubated in microtitre plates was revealed. It was concluded that this method is of great potential use as an early predictive indicator of egg viability. The effect of temperature on egg production was studied in two broodstock groups held either at ambient or low stable temperature during spawning. High temperatures caused a delay and shortening of the spawning period as well as a reduction in egg quantity and quality. The results indicated that temperature control is a necessary feature of broodstock management at sites where ambient temperature profiles are unsuitable. The efficacy of hydrostatic pressure shocking for the induction of triploidy was tested on newly fertilised eggs. A 5 min pressure shock of 8500 psi, administered around 15 min after fertilisation resulted in high triploidy yields. This treatment had little effect on survival to hatching. However, a preliminary experiment indicated that triploid halibut may be prone to higher mortality through the hatchery cycle. Six weaning experiments were conducted to determine the influence of size, age, and developmental stage of halibut larvae on diet uptake, survival, growth and fry quality. Gradual replacement of Artemia with dry diet, co-feeding, and the use of intermediate diet types, were evaluated. In the absence of live prey, pre-metamorphic larvae (< 100 mg) would accept non-living feed particles but total replacement with a conventional dry diet was unsuccessful. However, following good growth prior to weaning, 700 “day old larvae could be successfully weaned over a nine day period. Improved growth and substantial savings in live feed were among the positive benefits resulting from early weaning

Fish behavior and its use in the capture and culture of fishes

Fishery management, Behaviour, Food fish, Fish culture, Conferences

Genetic parameter estimations of new traits of morphological quality on gilthead seabream (Sparus aurata) by using IMAFISH_ML software

In this study, a total of 18 novel productive traits, three related to carcass [cNiT] and fifteen related to morphometric [mNiT]), were measured in gilthead seabream (Sparus aurata) using Non-invasive Technologies (NiT) as implemented in IMAFISH_ML (MatLab script). Their potential to be used in industrial breeding programs were evaluated in 2348 offspring reared under different production systems (estuarine ponds, oceanic cage, inland tank) at harvest. All animals were photographed, and digitally measured and main genetic parameters were estimated. Heritability for growth traits was medium (0.25–0.37) whereas for NiT traits medium-high (0.24–0.61). In general, genetic correlations between mNiT, cNiT and growth and traits were high and positive. Image analysis artifacts such as fin unfold or shades, that may interfere in the precision of some digital measurements, were discarded as a major bias factor since heritability of NiT traits after correcting them were no significantly different from original ones. Indirect selection of growth traits through NiT traits produced a better predicted response than directly measuring Body Weight (13–23%), demonstrating that this methodological approach is highly cost-effective in terms of accuracy and data processing time.Versión del edito

Genetic parameter estimations of new traits of morphological quality on gilthead seabream (Sparus aurata) by using IMAFISH_ML software

© 2021 The Authors.In this study, a total of 18 novel productive traits, three related to carcass [cNiT] and fifteen related to morphometric [mNiT]), were measured in gilthead seabream (Sparus aurata) using Non-invasive Technologies (NiT) as implemented in IMAFISH_ML (MatLab script). Their potential to be used in industrial breeding programs were evaluated in 2348 offspring reared under different production systems (estuarine ponds, oceanic cage, inland tank) at harvest. All animals were photographed, and digitally measured and main genetic parameters were estimated. Heritability for growth traits was medium (0.25–0.37) whereas for NiT traits medium-high (0.24–0.61). In general, genetic correlations between mNiT, cNiT and growth and traits were high and positive. Image analysis artifacts such as fin unfold or shades, that may interfere in the precision of some digital measurements, were discarded as a major bias factor since heritability of NiT traits after correcting them were no significantly different from original ones. Indirect selection of growth traits through NiT traits produced a better predicted response than directly measuring Body Weight (13–23%), demonstrating that this methodological approach is highly cost-effective in terms of accuracy and data processing time.This study was funded from the European Maritime and Fisheries Fund (EMFF) by Ministerio de Agricultura y Pesca, Alimentación y Medio Ambiente (MAPAMA), framed in PROGENSA-II III project (Mejora de la Competitividad del Sector de la Dorada a Través de la Selección Genética, programa JACUMAR)