Elevated temperature promotes growth and feed efficiency of farmed ballan wrasse juveniles (Labrus bergylta)

The expansion of ballan wrasse farming, used as a biological control against sea lice in Atlantic salmon, is constrained by the slow growth rate in the species and extended period required to reach deployment size. Rearing temperature and diets are the two main growth limiting factors in fish. In this study, farmed ballan wrasse juveniles were reared at 10, 13 and 16 °C over a period of 3 months and fed two different commercial diets commonly used in marine finfish, Otohime S2 and BioMar Symbio. At the end of the trial, fish growth was +125, +75 and + 25% compared to their initial weight in 16, 13 and 10 °C treatments, respectively. It was suggested that temperatures above 16 °C may promote growth even further. Furthermore, feed conversion ratio was significantly improved in fish reared at 16 °C. However, diets did not impact on any of the growth performance indicators although a significantly higher daily feed intake was observed in fish fed BioMar Symbio. Importantly, no significant effects of temperature and diets on mortality and condition factor were observed. No differences were found in the fish (whole-body) macronutrient composition between diets. Analysis of the protein, lipid and energy digestibility revealed lower apparent digestibility coefficients than normally observed in marine species, suggesting the diet formulation is not optimised for the species. Finally, fish reared at 10 °C showed increased hepatosomatic index, suggesting fat storage in the liver under cold temperatures. These results showed that the production cycle could be shortened by >4 months in fish reared at 16 °C. This could contribute to increase hatchery productivity and meet demand from the salmon production sector while reducing costs associated with the nursery phase although maintaining a constant high temperature would increase operational costs

Enriching Artemia nauplii with selenium from different sources and interactions with essential fatty acid incorporation

The production of high-quality marine fish fry is limited by the low survival observed during the larval phase, which is often attributed to dietary deficiencies of the diets at first feeding. Despite progress made with live feed (i.e. rotifers, Artemia), enrichments in essential fatty acids for marine fish larvae, little is known on the micronutrient requirements such as selenium (Se). Se is a critical component of several enzymes maintaining important biological functions such as cellular oxidation, and therefore plays a key role in oxidative and stress status of marine larvae. The levels of Se found in the larvae's natural diet (i.e. copepods) is generally higher than those of the enriched live preys used in hatcheries. This study aimed at establishing a protocol to enrich Artemia nauplii with Se using different inorganic (sodium selenite) and organic (selenoyeast). Results indicated that the use of dissolved sodium selenite, an alternative inorganic and cheaper form of Se, did not increase the levels of Se in the nauplii. However, the use of selenoyeast (Sel-Plex) confirmed that it is possible to enrich the nauplii with targeted levels of Se, since this process followed a dose-response pattern with Se enrichment ranging from 1.7 to 12.4 mg kg−1. In addition, the supplementation of Sel-Plex to the regular enrichment product did not impact on lipids and fatty acids enrichment irrespective of the dose dispensed. Overall, this study contributes to the refinement of the live prey enrichment protocols that are critical to the success of marine finfish larviculture protocols

Short-term lecithin enrichments can enhance the phospholipid and DHA contents of the polar lipid fraction of Artemia nauplii

Wild copepods are the main natural diet of marine finfish and they meet the larvae's requirements in phospholipids and essential fatty acids (EFA). While Artemia nauplii are an easier and more reliable live feed to produce in hatcheries for marine fish larvae than wild zooplankton, enrichment products commercially used lack phospholipids and essential long-chain polyunsaturated fatty acids (LC-PUFA). This is particularly true for docosahexaenoic acid (DHA) within their polar lipid fraction (PLDHA), which is critical to the survival and good development of the larvae. In this study, we showed that it is possible to increase the levels of phospholipids and DHA within the PL fraction of Artemia nauplii using marine lecithin through a process referred to as “boosting”. A cheaper alternative to marine lecithin, soya lecithin, was also tested but resulted only in a significant increase of the phospholipid content of the nauplii with no positive effect on the essential LC-PUFA levels, due to the absence of LC-PUFA in the soya lecithin. This study also showed that the levels of PLDHA in the Artemia boosted with marine lecithin did not reflect the levels of PLDHA in the lecithin, highlighting there the complexity of the boosting process. Finally, chilling enriched Artemia nauplii at 5 °C for up to 10 h did not impact on their nutritional quality post-enrichment. Ultimately, this study proposes innovative and sound enrichment strategies to produce Artemia nauplii rich in EFA and/or PL, similarly to that of the wild copepods' lipid profile

Development of genomic markers associated to growth-related traits and sex determination in lumpfish (Cyclopterus lumpus)

Cleaner fish species have gained great importance in the control of sea lice, among them, lumpfish (Cyclopterus lumpus) has become one of the most popular. Lumpfish life cycle has been closed, and hatchery reproduction is now possible, however, current production is reliant on wild caught broodstock to meet the increasing demand. Selective breeding practices are called to play an important role in the successful breeding of most aquaculture species, including lumpfish. In this study, we analysed a lumpfish population for the identification of genomic markers linked to production traits. Sequencing of RAD libraries allowed us to identify, 7193 informative markers within the sampled individuals. Genome wide association analysis for sex, weight, condition factor and standard length was performed. One single major QTL region was identified for sex, while nine QTL regions were detected for weight, and three QTL regions for standard length. A total of 177 SNP markers of interest (from QTL regions) and 399 high Fst SNP markers were combined in a low-density panel, useful to obtain relevant genetic information from lumpfish populations. Moreover, a robust combined subset of 29 SNP markers (10 associated to sex, 14 to weight and 18 to standard length) provided over 90% accuracy in predicting the animal's phenotype by machine learning. Overall, our findings provide significant insights into the genetic control of important traits in lumpfish and deliver important genomic resources that will facilitate the establishment of selective breeding programmes in lumpfish

Optimisation of the hatchery production of ballan wrasse (Labrus bergylta) with an emphasis on nutritional and environmental requirements

Ballan wrasse (Labrus bergylta), successfully used as a biological delouser of Atlantic salmon (Salmo salar), are eco-friendlier alternative to the use of chemotherapeutants. However, the use of wild caught specimens, which account for most of the deployed fish, is not sustainable. Therefore, the industry wishes to transition to farmed ballan wrasse, seen as a more sustainable, reliable and predictable source. However, the hatcheries are facing production challenges common to any new marine fish species including low survival, suboptimal growth, poor feed efficiency and lack of robustness that hampers the up-scaling of the production. To increase hatchery productivity, this doctoral project investigated the nutritional and environmental requirements of the species to develop commercial protocols. The first two experimental chapters focused on live feed (e.g. Artemia) enrichment for ballan wrasse larvae especially for phospholipids and essential fatty acids (chapter II) and selenium (chapter III). Chapter II proposes an effective, simple and easy method for simultaneously boosting the phospholipid and essential fatty acids content of the nauplii. In chapter III, an enrichment protocol was created allowing the hatcheries to target specific selenium contents in their nauplii. Then, research looked at the impact of three temperatures (10, 13 and 16 °C) on juveniles feed intake, growth and digestibility (chapter IV). Results showed that growth performances and feed efficiency were greatly improved at 16 °C compared to the lower temperatures. If implemented commercially, this could shorten the on-growing nursery phase by more than four months. Chapter V then studied the effects of dietary protein content (standard 51% vs. high 59 % crude protein) and protein source (fish meal vs plant-based) on the growth performances, feed efficiency and digestibility of juveniles reared at 15 °C. The study showed the successful substitution of fish meal by soy protein concentrate and pea protein, without compromising growth nor fish condition. In addition, fish fed the standard protein diets saw their feed efficiency improved, while signs of mild enteritis were observed in fish fed the high protein diets. Finally, the last experimental study (chapter VI) in this project consisted in a large-scale screening for deformities in the Scottish production of ballan wrasse. Results clearly showed a high prevalence of jaw, operculum and vertebrae malformations as well as the recurrent presence of nephrocalcinosis, at both post-weaning and pre-deployment stages. While this is not unusual in new emerging marine species in aquaculture, aetiology and mitigation measures will need to be developed to ensure both fish welfare and delousing efficacy. Overall, this PhD contributes to the refinement of the rearing protocols and development of suitable diets for ballan wrasse which will contribute to boost hatchery productivity and cleaner fish welfare

Optimisation of the hatchery production of Ballan wrasse (Labrus bergylta) with an emphasis on nutritional and environmental requirements

Tesis doctoral presentada para optar al grado de Doctor por la Universidad de Stirling.--2019-12-09.--AptoBallan wrasse (Labrus bergylta), successfully used as a biological delouser of Atlantic salmon (Salmo salar), are eco-friendlier alternative to the use of chemotherapeutants. However, the use of wild caught specimens, which account for most of the deployed fish, is not sustainable. Therefore, the industry wishes to transition to farmed ballan wrasse, seen as a more sustainable, reliable and predictable source. However, the hatcheries are facing production challenges common to any new marine fish species including low survival, suboptimal growth, poor feed efficiency and lack of robustness that hampers the up-scaling of the production. To increase hatchery productivity, this doctoral project investigated the nutritional and environmental requirements of the species to develop commercial protocols. The first two experimental chapters focused on live feed (e.g. Artemia) enrichment for ballan wrasse larvae especially for phospholipids and essential fatty acids (chapter II) and selenium (chapter III). Chapter II proposes an effective, simple and easy method for simultaneously boosting the phospholipid and essential fatty acids content of the nauplii. In chapter III, an enrichment protocol was created allowing the hatcheries to target specific selenium contents in their nauplii. Then, research looked at the impact of three temperatures (10, 13 and 16 °C) on juveniles feed intake, growth and digestibility (chapter IV). Results showed that growth performance and feed efficiency were greatly improved at 16 °C which is implemented commercially could shorten the on-growing nursery phase by more than four months. Chapter V then studied the effects of dietary protein content (standard 51% vs. and high 59 % crude protein) and protein source (fish meal vs plant-based). Results showed fish fed the standard protein diets had a higher feed efficiency while signs of mild enteritis were observed in fish fed the high protein diets. Another important finding from this study was the successful substitution of fish meal by soy protein concentrate and pea protein, without compromising growth nor fish condition. Finally, the last experimental study (chapter VI) in this project consisted in a large-scale screening for deformities in the Scottish production of ballan wrasse. Results clearly showed a high prevalence of jaw, operculum and vertebrae malformations as well as the recurrent presence of nephrocalcinosis, at both post-weaning and pre-deployment stages. While this is not unusual in new emerging marine species in aquaculture, aetiology and mitigation measures will need to be developed to ensure both fish welfare and delousing efficacy. Overall, this PhD contributes to the refinement of the rearing protocols and development of suitable diets for ballan wrasse which will contribute to boost hatchery productivity and cleaner fish welfare.Peer reviewe

Deformities prevalence in farmed ballan wrasse (Labrus bergylta) in relation to hatchery origin and life stage

The production of farmed ballan wrasse (Labrus bergylta) is developing, with an emphasis on sustainability and quality. However, ballan wrasse hatcheries have anecdotally reported increased prevalence of malformations which may impact on fish welfare and hatchery productivity. The present study therefore aimed to identify and characterise deformities in two of the largest ballan wrasse producers in the UK. A total of 384 farmed fish were sampled at two life stages (post-weaning and pre-deployment) and independent production runs. Additionally, 25 wild caught ballan wrasse were analysed and used as a reference. Each fish was externally examined for malformations including jaw and operculum deformities. The fish were internally examined by x-ray for vertebral deformities and abnormalities of the swim bladder. Mineral analysis of both whole fish and vertebrae were also conducted. The results showed the first information on the ballan wrasse skeleton structure. The total number of vertebrae per fish ranged from 34 to 37, with 37 vertebrae per fish representing 58.2% of all fish analysed. The vertebral column was divided into two regions, namely R1 and R2. R1 included vertebrae 1 to 17 (post-cranial and pre-haemal vertebrae) while R2 included vertebrae 18 to 34–37 (haemal vertebrae and haemal caudal vertebrae). Results showed a high prevalence of vertebrae malformations (up to 33%), jaw/operculum malformations (up to 13.5%) and nephrocalcinosis (up to 25%), with high severity levels in some cases when compared to wild specimens in which malformations were absent. Most malformations were already visible at post-weaning. Wild fish did not show signs of any malformations. Finally, high mineral diets are suggested as a potential route of investigation to reduce the vertebral deformities in ballan wrasse. Increasing the productivity of cleaner fish hatcheries is key to addressing the on-going challenge of sea lice in Atlantic salmon (Salmo salar) farming. It is therefore of paramount importance that the causes of the presently identified pathologies are confirmed and mitigation steps introduced

Elevated temperature promotes growth and feed efficiency of farmed ballan wrasse juveniles (Labrus bergylta)

The expansion of ballan wrasse farming, used as a biological control against sea lice in Atlantic salmon, is constrained by the slow growth rate in the species and extended period required to reach deployment size. Rearing temperature and diets are the two main growth limiting factors in fish. In this study, farmed ballan wrasse juveniles were reared at 10, 13 and 16 °C over a period of 3 months and fed two different commercial diets commonly used in marine finfish, Otohime S2 and BioMar Symbio. At the end of the trial, fish growth was +125, +75 and + 25% compared to their initial weight in 16, 13 and 10 °C treatments, respectively. It was suggested that temperatures above 16 °C may promote growth even further. Furthermore, feed conversion ratio was significantly improved in fish reared at 16 °C. However, diets did not impact on any of the growth performance indicators although a significantly higher daily feed intake was observed in fish fed BioMar Symbio. Importantly, no significant effects of temperature and diets on mortality and condition factor were observed. No differences were found in the fish (whole-body) macronutrient composition between diets. Analysis of the protein, lipid and energy digestibility revealed lower apparent digestibility coefficients than normally observed in marine species, suggesting the diet formulation is not optimised for the species. Finally, fish reared at 10 °C showed increased hepatosomatic index, suggesting fat storage in the liver under cold temperatures. These results showed that the production cycle could be shortened by >4 months in fish reared at 16 °C. This could contribute to increase hatchery productivity and meet demand from the salmon production sector while reducing costs associated with the nursery phase although maintaining a constant high temperature would increase operational costs.The project and PhD studentship TCR were supported by a project co-funded by the Scottish Aquaculture Innovation Centre (SAIC) and industry partners

Plant-based protein ingredients can successfully replace fish meal in the diet of ballan wrasse (LABRUS BERGYLTA) juveniles

The production of ballan wrasse is hampered by the poor growth and feeding performances and lack of robustness of the species in culture, which is often attributed to sub-optimal nutrition. The commercial marine finfish diets used in ballan wrasse hatcheries, rich in marine ingredients, may not fulfil the species nutritional requirements. This study aimed at evaluating the effects of plant-based ingredients inclusion on the growth, survival, feeding response and digestibility of the species. Simultaneously, the effects of two dietary protein levels were investigated. Ballan wrasse juveniles at approximately 5 g were reared at 15 °C for 70 days. Three Marine Protein:Plant Protein ratios (3.4, 1.6 and 0.9) and two protein contents (51 and 59% CP) were studied, resulting in five experimental diets and one commercial control diet, tested in triplicate. The partial replacement of fish meal by plant-based ingredients was shown to not compromise growth, survival and feed efficiency. Fish fed the Standard CP diets (51% CP) showed a significantly lower FCR (1.2 ± 0.1) compared to fish fed High CP diets (59% CP) (1.4 ± 0.2). Regarding daily feed intake, fish fed the Standard CP diets ate less (1.4 ± 0.2% day−1) than fish fed the High CP diets (1.6 ± 0.1% day−1). Signs of enteritis were observed in two out of three High CP diets. The use of plant-based ingredients, more cost-effective and sustainable than fish meal, has a great potential for the species as they reflect better natural feeding of wild populations thus may promote the hatcheries productivity by reducing feed costs while improving their sustainability index. The study shows that a potential route for optimising diet formulation for ballan wrasse may lie within carbohydrate and lipid contents. Overall, this research contributes to the development of ballan wrasse on-growing feeds to promote the development of ballan wrasse aquaculture and its benefits on sea lice mitigation

Short-term lecithin enrichments can enhance the phospholipid and DHA contents of the polar lipid fraction of Artemia nauplii

Wild copepods are the main natural diet of marine finfish and they meet the larvae's requirements in phospholipids and essential fatty acids (EFA). While Artemia nauplii are an easier and more reliable live feed to produce in hatcheries for marine fish larvae than wild zooplankton, enrichment products commercially used lack phospholipids and essential long-chain polyunsaturated fatty acids (LC-PUFA). This is particularly true for docosahexaenoic acid (DHA) within their polar lipid fraction (PL), which is critical to the survival and good development of the larvae. In this study, we showed that it is possible to increase the levels of phospholipids and DHA within the PL fraction of Artemia nauplii using marine lecithin through a process referred to as “boosting”. A cheaper alternative to marine lecithin, soya lecithin, was also tested but resulted only in a significant increase of the phospholipid content of the nauplii with no positive effect on the essential LC-PUFA levels, due to the absence of LC-PUFA in the soya lecithin. This study also showed that the levels of PL in the Artemia boosted with marine lecithin did not reflect the levels of PL in the lecithin, highlighting there the complexity of the boosting process. Finally, chilling enriched Artemia nauplii at 5 °C for up to 10 h did not impact on their nutritional quality post-enrichment. Ultimately, this study proposes innovative and sound enrichment strategies to produce Artemia nauplii rich in EFA and/or PL, similarly to that of the wild copepods' lipid profile.The project and T. Cavrois Rogacki PhD studentship were co-funded by the Scottish Aquaculture Innovation Centre (SAIC) and University of Stirlin