Application of passive-acoustic telemetry to explore the behaviour of ballan wrasse (Labrus bergylta) and lumpfish (Cyclopterus lumpus) in commercial Scottish salmon sea-pens

A passive-acoustic telemetry system was used for the first time for the fine-scale, three-dimensional tracking of individual cleaner fish in commercial Scottish salmon sea-pens in full commercial operation. The aim was to test the system performance and provide baseline data on the comparative distribution and swimming activity of individual ballan wrasse and lumpfish under standard farm practices with the long-term aim of informing stocking and husbandry strategies. In March 2015, wild ballan wrasse (Labrus bergylta) (115 ± 20 g; n = 13) and farmed lumpfish (Cyclopterus lumpus) (281 ± 42 g; n = 13) previously deployed in June–October 2014 were recaptured, implanted with acoustic tags pinging every 6–12 s and released into their original sea cage holding Atlantic salmon (Q2 2014; 2059 ± 35 g mean-weight). Control tags were deployed in cleaner fish hides to validate the system performance. Positional data from nine specimens per species were analysed from March 24th to June 1st 2015, during which time water temperature rose from 7.2 to 9.1 °C and water salinity averaged 26.8 ± 1.5 ppt at 4 m depth. The accuracy of the acoustic positions averaged 0.6 m across the three dimensions of all control tags and was < 1 m in 93% of all cases. Significant differences in the distribution and activity of ballan wrasse and lumpfish were observed. Ballan wrasses spent 60 ± 2% of the day-time at or below 15 m, were positioned at significantly shallower depths at night and seldom used the hides provided despite an apparent resting behaviour at the pen bottom and corners. In comparison, lumpfish spent over 80% of the time above 10 m, used hides extensively and preferentially at night (50.1 ± 2.1% at night), but to a lesser extent when the water temperature increased. The acoustic tracking system proved to be an effective tool for visualising cleaner fish behaviour under challenging farm conditions, and the study highlights the critical role of hides in cleaner fish husbandry. Overall, the study quantified species-specific cleaner fish distribution in salmon net-pens supporting distinct interactions with the salmon stock and seasonal behaviour profiles. The results support the current commercial strategy of using two cleaner fish species against sea lice and the need for species-specific management strategies to optimise delousing activity

Effects of temperature on feed intake and plasma chemistry after exhaustive exercise in triploid brown trout (Salmo trutta L)

The physiological effect of temperature on feed intake and haematological parameters after exhaustive swimming in diploid and triploid brown trout (Salmo trutta) was investigated. Trout were exposed to an incremental temperature challenge (2 degrees C/day) from ambient (6 degrees C) to either 10 or 19 degrees C. Feed intake profiles did not differ between ploidy at 10 degrees C; however, triploids had a significantly higher total feed intake at 19 degrees C. After 24 days, each temperature-ploidy group was exposed to exhaustive swimming for 10 min. The haematological response differed between ploidy, with the magnitude of the response affected by temperature and ploidy. Post-exercise, acid-base and ionic differences were observed. Plasma lactate increased significantly from rest for both temperature and ploidy groups, but glucose increased significantly at higher temperature. Post-exercise, triploids at 19 degrees C had significantly higher osmolality and cholesterol than diploids, but differences were resumed within 4 h. Elevated alkaline phosphatase (ALP) and aspartate aminotransferase (AST) in fish at higher temperature suggested greater tissue damage; however, both ploidy responded similarly. Despite no significant differences in deformity prevalence, the type and location of deformities observed differed between ploidy (decreased intervertebral space with higher prevalence in tail area and fin regions for diploids, while vertebral compression, fusion in cranial and caudal trunks for triploids). These results suggest triploids have greater appetite than diploids at elevated temperature and that triploids suffer similar blood disturbances after exercise as diploids. These findings have implications for the management of freshwater ecosystems and suggest that stocking triploid brown trout may offer an alternative to diploid brown trout

Genetic diversity and structure in Arapaima gigas populations from Amazon and Araguaia-Tocantins river basins

Background Arapaima gigas (Schinz, 1822) is the largest freshwater scaled fish in the world, and an emerging species for tropical aquaculture development. Conservation of the species, and the expansion of aquaculture requires the development of genetic tools to study polymorphism, differentiation, and stock structure. This study aimed to investigate genomic polymorphism through ddRAD sequencing, in order to identify a panel of single nucleotide polymorphisms (SNPs) and to simultaneously assess genetic diversity and structure in wild (from rivers Amazon, Solimões, Tocantins and Araguaia) and captive populations. Results Compared to many other teleosts, the degree of polymorphism in A. gigas was low with only 2.3% of identified RAD-tags (135 bases long) containing SNPs. A panel of 393 informative SNPs was identified and screened across the five populations. Higher genetic diversity indices (number of polymorphic loci and private alleles, Shannon’s Index and HO) were found in populations from the Amazon and Solimões, intermediate levels in Tocantins and Captive, and very low levels in the Araguaia population. These results likely reflect larger population sizes from less urbanized environments in the Amazon basin compared to Araguaia. Populations were significantly differentiated with pairwise FST values ranging from 0.086 (Amazon × Solimões) to 0.556 (Amazon × Araguaia). Mean pairwise relatedness among individuals was significant in all populations (P

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

Pre-deployment acclimatisation of farmed ballan wrasse (Labrus bergylta) to sea-cage conditions promotes behaviour analogous to wild conspecifics when used as cleaner fish in Atlantic salmon (Salmo salar) farms

Ballan wrasse (Labrus bergylta) are used as cleaner fish in commercial Atlantic salmon farming to remove ectoparasitic sea lice. While the delousing performance of wild wrasse is usually good, that of farmed wrasse is variable, possibly because of different conditions in hatcheries and sea cages. In this study, three passive-acoustic telemetry (PAT) trials were conducted at a salmon farm to compare the behaviour of wild and farmed wrasse and test the effect of acclimatising farmed wrasse to sea-cage conditions before deployment. Up to 40 fish were monitored simultaneously for 60–124 days by triangulating tag positions within a hydrophone array every 6–10 s. This data was used to assess fish depth and preferred cage locations and calculate activity, orientation and home ranges. Wild wrasse occupied shallower depths (13.3 ± 2.4 m) than farmed wrasse, which remained near the bottom of the cages (18.2 ± 1.7 m). Swimming activity was higher in wild wrasse with significant diurnal variations due to nocturnal quiescence on 68% of observed days. Wild wrasse rapidly developed large home ranges (616.8 ± 110.1 m2), preferring cage corners. Hatchery-and-sea-cage acclimatisation improved the behaviour of farmed wrasse; they rapidly moved up the water column (9.08 ± 2.05 m after 1 week) and established home ranges (514.3 ± 146.6 m2), and they developed diurnal activity patterns, which may indicate a positive response to acclimatisation. Acclimatising farmed ballan wrasse to sea-cage conditions positively improved and encouraged behaviours similar to those seen in wild wrasse, including diurnal rhythms and the establishment of home ranges, and is recommended for all farmed wrasse prior to deployment to improve delousing performance

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

Investigating the kisspeptin system in the hermaphrodite teleost gilthead seabream (Sparus aurata)

The kisspeptin system, a known regulator of reproduction in fish, was investigated during two key phases within the gilthead seabream (Sparus aurata) life cycle: protandrous sex change and larval ontogeny. Seabream specific partial cDNA sequences were identified for two key targets, kissr4 and kiss2, which were subsequently cloned and qPCR assays developed. Thereafter, to examine association in expression with sex change, a group of adult seabream (2+ years old) undergoing sex change were sampled for gene expression at two different periods of the annual cycle. To study the kisspeptin system ontogeny during early life stages, transcript levels were monitored in larvae (till 30 days-post-hatch, DPH) and post-larvae (from 30 till 140 DPH). During sex change, higher expression of kissr4 and kiss2 was observed in males when compared to females or individual undergoing sex change, this is suggestive of differential actions of the kisspeptin system during protandrous sex change. Equally, variable expression of the kisspeptin system during early ontogenic development was observed. The higher expression of kissr4 and kiss2 observed from 5 DPH, with elevations at 5–20 and 90 DPH for kissr4 and at 5, 10, 20, and 60 DPH for kiss2, is coincident with the early ontogeny of gnrh genes previously reported for seabream, and possibly related with early development of the reproductive axis in this species

High resolution longitudinal eDNA metabarcoding and morphological tracking of planktonic threats to salmon aquaculture

Salmonid aquaculture, a major component of the Northern European, North American, and Chilean coastal economies, is under threat from challenges to gill health, many of which originate from plankton communities. A first step toward mitigating losses is to characterize the biological drivers of poor gill health. Numerous planktonic taxa have been implicated, including toxic and siliceous microalgae, hydrozoans, and scyphozoans; however, rigorous longitudinal surveys of plankton diversity and gill health have been lacking. In the current study, we present and assess an exhaustive identification approach combining both morphological and molecular methods together with robust statistical models to identify the planktonic drivers of proliferative gill disease (PGD) and fish mortality. We undertook longitudinal evaluation at two marine aquaculture facilities on the west coast of Scotland using daily data collected during the 2021 growing season (March–October). Examining these two different sites, one sheltered and one exposed to the open sea, we identified potentially new, important, and unexpected planktonic drivers of PGD and mortality (e.g., doliolids and appendicularians) and confirmed the significance of some established threats (e.g., hydrozoans and diatoms). We also explored delayed or “lagged” effects of plankton abundances on gill health and undertook a comparison of environmental DNA (eDNA) metabarcoding and microscopy in their ability to identify and quantify planktonic species. Our data highlight the diversity of planktonic threats to salmonid aquaculture as well as the importance of using both molecular and morphological approaches to detect these. There is now an urgent need to expand systematic longitudinal molecular and morphological approaches across multiple sites and over multiple years. The resultant catalogue of main biological drivers will enable early warning systems, new treatments, and, ultimately, a sustainable platform for future salmonid aquaculture in the marine environment

Comparative proteome and peptidome analysis of the cephalic fluid secreted by Arapaima gigas (Teleostei: Osteoglossidae) during and outside parental care

Parental investment in Arapaima gigas includes nest building and guarding, followed by a care provision when a cephalic fluid is released from the parents&rsquo; head to the offspring. This fluid has presumably important functions for the offspring but so far its composition has not been characterised. In this study the proteome and peptidome of the cephalic secretion was studied in parental and non-parental fish using capillary electrophoresis coupled to mass spectrometry (CE-MS) and GeLC-MS/MS analyses. Multiple comparisons revealed 28 peptides were significantly different between males and parental males (PC-males), 126 between females and parental females (PC-females), 51 between males and females and 9 between PC-males and PC-females. Identification revealed peptides were produced in the inner ear (pcdh15b), eyes (tetraspanin and ppp2r3a), central nervous system (otud4, ribeye a, tjp1b and syn1) among others. A total of 422 proteins were also identified and gene ontology analysis revealed 28 secreted extracellular proteins. From these, 2 hormones (prolactin and stanniocalcin) and 12 proteins associated to immunological processes (serotransferrin, &alpha;-1-antitrypsin homolog, apolipoprotein A-I, and others) were identified. This study provides novel biochemical data on the lateral line fluid which will enable future hypotheses-driven experiments to better understand the physiological roles of the lateral line in chemical communication

Dietary supplementation with a specific mannan-rich yeast parietal fraction enhances the gut and skin mucosal barriers of Atlantic salmon (Salmo salar) and reduces its susceptibility to sea lice (Lepeophtheirus salmonis)

Background: Increasing reliance on non-medicinal interventions to control sea lice in the Atlantic salmon (Salmo salar) farming industry imposes a high level of skin mucosal disturbance and indirect health issues. Dietary supplementation with yeast-based MOS products is widely used to support intestinal homeostasis across farmed species. Evidence of their effect on skin mucosa is increasing in aquatic species but it remains inconsistent and someway short of a clear contribution to sea lice management. A tank-based trial was performed to test the effect of a yeast-based MOS functional compound (sMOS) on the skin mucosal layer and its protective effects against sea lice (Lepeophtheirus salmonis). Results: The test compound significantly increased skin mucus (+46%) and goblet cell density (+25%) after 6 weeks of dietary supplementation when positive effects on intestinal villi-length (+10.9%) and goblet cell density (+80.0%) were also documented. Following dietary supplementation, a 16.6% reduction in susceptibility to an acute standard copepodid challenge was measured alongside an earlier increase in skin lysozyme activity widely used as an index of innate immunity. Conclusion: The study provides functional evidence that the benefits of dietary sMOS reach beyond the intestine to the skin mucosa. Bolstering of the Atlantic salmon skin barrier and immune functions and the resulting lower susceptibility to sea lice has the potential to reduce the need for delousing interventions and the impact of non-medicinal interventions on the animal's health and welfare