Progress in modeling quality in aquaculture: an application of the Self‐Organizing Map to the study of skeletal anomalies and meristic counts in gilthead seabream (Sparus aurata,L. 1758)

One of the most common drawbacks of artificial life conditions imposed by aquaculture is the quite high presence of skeletal anomalies (SAs) in reared fish, which reduce both functional performances and marketing image/commercial value of the reared lots. Thus, skeletal malformations and their incidence are one of the most important factors affecting fish farmer’s production costs, and several efforts have been due to develop appropriate tools in detecting patterns of co‐variation among rearing parameters and fish quality. In this paper we explore the advantages of using Self‐Organized Maps (SOMs) when dealing with the analysis of correlations between the pattern of SA presence and rearing parameters in gilthead seabream (Sparus aurata L.), that is a largely reared fish of high commercial value. SOM, which is one of the best known neural networks with unsupervised learning rules, were applied to develop a model of the occurrence of SAs, both in terms of type and quantity, in seabream lots from different rearing approaches (extensive, semi‐intensive and intensive). The trained SOMs classified lots according to the variation observed in the different weights of SAs, but also allows the detection of a series of correspondence, namely between: (i) the patter of SAs occurrence and the different rearing approach currently used in seabream aquaculture; and (ii) the total SAs incidence and the variability of meristic counts, represent a completely independent dataset. Mesocosms resulted the best rearing approach to produce wild‐like fish, whereas intensive rearing is characterized by the large presence of SA. Globally, results suggested that this approach is reliable to be used for estimate the distance between aquaculture products and the wild‐like phenotype used as quality reference.     

Aquacultured Rainbow Trout (Oncorhynchus mykiss) Possess a Large Core Intestinal Microbiota That Is Resistant to Variation in Diet and Rearing Density

As global aquaculture fish production continues to expand, an improved understanding of how environmental factors interact in fish health and production is needed. Significant advances have been made toward economical alternatives to costly fishmeal-based diets, such as grain-based formulations, and toward defining the effect of rearing density on fish health and production. Little research, however, has examined the effects of fishmeal- and grain-based diets in combination with alterations in rearing density. Moreover, it is unknown whether interactions between rearing density and diet impact the composition of the fish intestinal microbiota, which might in turn impact fish health and production. We fed aquacultured adult rainbow trout (Oncorhynchus mykiss) fishmeal- or grain-based diets, reared them under high- or low-density conditions for 10 months in a single aquaculture facility, and evaluated individual fish growth, production, fin indices, and intestinal microbiota composition using 16S rRNA gene sequencing. We found that the intestinal microbiotas were dominated by a shared core microbiota consisting of 52 bacterial lineages observed across all individuals, diets, and rearing densities. Variations in diet and rearing density resulted in only minor changes in intestinal microbiota composition despite significant effects of these variables on fish growth, performance, fillet quality, and welfare. Significant interactions between diet and rearing density were observed only in evaluations of fin indices and the relative abundance of the bacterial genus Staphylococcus. These results demonstrate that aquacultured rainbow trout can achieve remarkable consistency in intestinal microbiota composition and suggest the possibility of developing novel aquaculture strategies without overtly altering intestinal microbiota composition.     

Studies on the appearance of skeletal anomalies in red porgy: effect of culture intensiveness,feeding habits and nutritional quality of live preys

Despite the great interest of red porgy as a new species for Mediterranean aquaculture, its commercial production is constrained by the high incidence of skeletal deformities occurring in this species under culture conditions. Several studies have been conducted to better understand the origin of these anomalies in this species, using different system intensiveness, rotifers enrichment products or rotifers docosahexaenoic acid content. The first study showed that culture intensification increased the number of fish with an extra vertebrae, what was probably related to the different nutritional quality of live preys employed in each treatment, since water temperature, salinity and genetic background were identical for the different batches of fish studied. Total incidence of skeletal abnormalities was higher in the intensive system, particularly cranial abnormalities and kyphosis in the cephalic vertebrae. In both rearing systems the most common skeletal anomalies were vertebral column disorders, lordosis and fused vertebrae, their localization along the column being affected by the culture intensiveness. Rotifer enrichment, predominantly its docosahexaenoic acid content significantly affected deformities occurrence. A marked positive effect of rotifer docosahexaenoic acid content was found on larval survival. X‐ray studies denoted elevated levels of bone abnormalities associated, in both trials, to low docosahexaenoic acid content in live preys. Among different anomalies, the presence of fused vertebrae was the most frequent deformity for both rearing trials. A 50% reduction in the number of deformed fish for each type of deformity was obtained when the larvae were fed higher docosahexaenoic acid levels, denoting the important role of this fatty acid in bone development. Further studies are needed to elucidate the importance of essential fatty acids on the development of bone deformities in fish, since the functions of these fatty acids differ among them and can lead to very different effects in fish metabolism, including bone formation.     

Use of meristic counts and skeletal anomalies to assess developmental plasticity of farmed rainbow trout (Oncorhynchus mykiss,Walbaum 1792): a preliminary study

Rainbow trout is the longest‐standing intensively‐reared species in Western countries, where it has been subjected by farmers to selection for productive traits for more than a century. One interesting aspect in this context is to try and understand if prolonged artificial selection has in some way altered the phenotypic plasticity of this species. In this preliminary study, we characterized meristic counts and skeletal abnormalities in two different (Italian and French) rainbow trout strains, reared during on‐growing following different approaches (intensive and semi‐intensive), in order to analyze whether there are any differences in the skeletal elements and if so, what. Despite the different genetic origin and rearing methodologies to which the lots analyzed were subjected, the occurrences of malformed and seriously malformed individuals were not significantly different, nor were the mean number of anomalies per specimen. The body region most affected by deformities was the caudal vertebral column in both lots, although the French lot was also characterized by an high occurrence of spinal anomalies in the haemal region. Among the meristic counts, only the number of anal and dorsal rays showed statistically different median values between the two lots.     

Effects of stress on growth, cortisol and glucose levels in non-domesticated Eurasian perch (Perca fluviatilis) and domesticated rainbow trout (Oncorhynchus mykiss)

Eurasian perch (Perca fluviatilis) is a promising aquaculture candidate, but the growth performance of this non-domesticated species may be negatively affected by its stress responsiveness to intensive culture conditions. To evaluate this potential problem, juvenile Eurasian perch were exposed to a standardized handling stressor twice a week for an 8-week period. A similar study was conducted on domesticated rainbow trout (Oncorhynchus mykiss) for comparison of intra- and inter-specific differences. The stressed fish of both species showed lower body growth than the non-stressed control fish, however, the final mean body mass was 35.4% lower in the stressed Eurasian perch than in the non-stressed controls, compared to 22.8% difference between the two groups in rainbow trout. The stress responsiveness was examined by comparing the post-stress cortisol and glucose levels in repeatedly stressed fish and fish exposed to the stressor only once. The cortisol stress response in both species strongly indicated a habituation to the repeated stressor. Thus, repeatedly stressed Eurasian perch reached maximum cortisol levels of 130 ng/mL after 0.5 h compared to 200 ng/mL in the fish stressed once, while considerably smaller differences in cortisol levels were shown between the repeatedly and single stressed rainbow trout. Rainbow trout also showed lower post-stress glucose levels in the repeatedly stressed fish compared to the single stressed fish. In contrast, the glucose levels in both groups of Eurasian perch increased abruptly after stress treatment and remained elevated at approximately 19 mM for 6 h; levels were three times as high as the peak levels 3 h post-stress in rainbow trout. Together, the habituation of the stress response shown in both species did not eliminate the growth difference found in the repeatedly stressed fish versus the control fish. Further, the lower growth performance of Eurasian perch compared to rainbow trout could partly be due to the increased energy consumption in the more stress responsive Eurasian perch.     

Effect of rearing techniques on skeletal deformities and osteological development in red porgy Pagrus pagrus (Linnaeus, 1758) larvae

Red porgy is a candidate species for marine aquaculture diversification. The objective of the present study was to describe the osteological development in this species and the occurrence of skeletal deformities in relation to the intensification of the rearing system. Fish samples were periodically collected along the development from hatching to juveniles (95 days after hatching). Osteological development and the presence of skeleton abnormalities were evaluated. Larvae reared under S‐IS showed a better growth in terms of total length in comparison with IS reared ones. Regarding to osteological development for red porgy, this was similar between fish from both culture systems, but differing in timing of apparition and ossification of skeletal elements. X‐ray studies revealed a high number of fish with skeletal deformities (Semi‐intensive: 38.8%; Intensive: 46.5%), but no significant effect of the rearing technique on the incidence of deformities such as lordosis or fused vertebrae was found. However, cranial abnormalities and kyphosis incidences were significantly higher in intensive system cultured red porgy. These results, suggest a relationship among rearing technique, osteological development and the apparition of certain deformities.     

State of gonads in juvenile triploid trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> under conditions of South Vietnam after artificial sex inversion

Gonad morphology and structure of sex cells in juvenile triploid trout Oncorhynchus mykiss of the Donaldson breed incubated and reared at a trout plant under climatic conditions of South Vietnam have been studied. Anomalies in the structure of sex gonads and oocyte structure were found, and partial resorption of sex cells was detected. It was shown that sex inversion in triploid (unisexual) fingerlings of rainbow trout passed successfully on the whole since many sex gonads of these fish simultaneously had both female and male sex cells and sometimes were sterile. The connection of anomalies found in the structure of sex system of trout with species rearing under unusual for it climatic conditions and artificial sex inversion is discussed.     

Environmental Conditioning of Skeletal Anomalies Typology and Frequency in Gilthead Seabream (Sparus aurata L., 1758) Juveniles

In this paper, 981 reared juveniles of gilthead seabream (Sparus aurata) were analysed, 721 of which were from a commercial hatchery located in Northern Italy (Venice, Italy) and 260 from the Hellenic Center for Marine Research (Crete, Greece). These individuals were from 4 different egg batches, for a total of 10 different lots. Each egg batch was split into two lots after hatching, and reared with two different methodologies: intensive and semi-intensive. All fish were subjected to processing for skeletal anomaly and meristic count analysis. The aims involved: (1) quantitatively and qualitatively analyzing whether differences in skeletal elements arise between siblings and, if so, what they are; (2) investigating if any skeletal bone tissue/ossification is specifically affected by changing environmental rearing conditions; and (3) contributing to the identification of the best practices for gilthead seabream larval rearing in order to lower the deformity rates, without selections. The results obtained in this study highlighted that: i) in all the semi-intensive lots, the bones having intramembranous ossification showed a consistently lower incidence of anomalies; ii) the same clear pattern was not observed in the skeletal elements whose ossification process requires a cartilaginous precursor. It is thus possible to ameliorate the morphological quality (by reducing the incidence of severe skeletal anomalies and the variability in meristic counts of dermal bones) of reared seabream juveniles by lowering the stocking densities (maximum 16 larvae/L) and increasing the volume of the hatchery rearing tanks (minimum 40 m³). Feeding larvae with a wide variety of live (wild) preys seems further to improve juvenile skeletal quality. Additionally, analysis of the morphological quality of juveniles reared under two different semi-intensive conditions, Mesocosm and Large Volumes, highlighted a somewhat greater capacity of Large Volumes to significantly augment the gap with siblings reared in intensive (conventional) modality.     

Melanin-based skin spots reflect stress responsiveness in salmonid fish

Within animal populations, genetic, epigenetic and environmental factors interact to shape individual neuroendocrine and behavioural profiles, conferring variable vulnerability to stress and disease. It remains debated how alternative behavioural syndromes and stress coping styles evolve and are maintained by natural selection. Here we show that individual variation in stress responsiveness is reflected in the visual appearance of two species of teleost fish; rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Salmon and trout skin vary from nearly immaculate to densely spotted, with black spots formed by eumelanin-producing chromatophores. In rainbow trout, selection for divergent hypothalamus–pituitary–interrenal responsiveness has led to a change in dermal pigmentation patterns, with low cortisol-responsive fish being consistently more spotted. In an aquaculture population of Atlantic salmon individuals with more spots showed a reduced physiological and behavioural response to stress. Taken together, these data demonstrate a heritable behavioural–physiological and morphological trait correlation that may be specific to alternative coping styles. This observation may illuminate the evolution of contrasting coping styles and behavioural syndromes, as occurrence of phenotypes in different environments and their response to selective pressures can be precisely and easily recorded.     

State of gonads of yearlings of triploid rainbow trout Oncorhynchus mykiss exposed to androgenic hormone under high-mountain conditions of South Vietnam

Changes in the morphology of gonads under the effect of methyltestosterone in juveniles of triploid rainbow trout Oncorhynchus mykiss incubated and cultivated in a trout farm under climatic conditions of South Vietnam have been studied. It was shown that the effect of the androgenic hormone intensifies the formation and development of testes in triploid rainbow trout at an age of 1+, decreasing the proportion of sterile individuals and the proportion of fish with anatomical and cytological anomalies in the structure of gonads. The relationship between the found anomalies in the structure of the genital system of trout and its triploidization, hormonal effect, and abiotic environmental conditions is discussed.     

Energy status and free fatty acid patterns in tissues of common carp (Cyprinus carpio,L.) and rainbow trout (Oncorhynchus mykiss,L.) during severe oxygen restriction

Common carp and rainbow trout were exposed to a severe level of oxygen restriction up to a near lethal value, to study the occurrence of tissue damage. Rainbow trout lost equilibrium at a PO₂ of 3.2 kPa, whereas carp were able to survive 1.5 hr of anoxia. In both species, the anaerobic metabolism was significantly activated and the energy status (PCr, ATP and energy charge) was significantly depressed in brain, liver, and red and white muscle. No marked release of PUFA to the FFA pool was observed, while membrane leakage was not increased as evidenced by plasma LDH-activity. These results indicate the absence of a marked hydrolysis of membrane lipids. Thus, even after a near lethal exposure to hypoxia or anoxia, no tissue damage occurs in fish liver and skeletal muscles. The changes of the FFA patterns in the skeletal muscles and liver of both species after oxygen deprivation may be related to changes in desaturase activities, a reduction of lipolytic activity and PUFA metabolism.     

Histomorphometrical studies of vertebral bone condition in farmed rainbow trout,Oncorhynchus mykiss

A major problem for the fish farming industry is to find reliable indicators of bone condition that could help to prevent vertebral abnormalities. Here, we summarize the main results of two recent studies aiming to assess the variation of two vertebral bone variables (bone mineralization and vertebral total bone area) during rainbow trout grow‐out in several French farms. We provide evidence for a wide range of variation for these parameters and for the occurrence of vertebral bone abnormalities, and new data on vertebral structure in trout reared either in various fish farms (influence of rearing conditions) or at different temperatures (influence of various growth rates). Although further experiments are needed to understand bone metabolism in trout, these findings increase our knowledge on growth and modelling of vertebrae, and provide valuable data that will enable comparisons in the future.     

Occurrence of skeletal deformities and osteological development in red porgy Pagrus pagrus larvae cultured under different rearing techniques

The present study describes the osteological development and the occurrence of skeletal deformities in red porgy Pagrus pagrus larvae in relation to the intensification of the rearing system. Eggs obtained from natural spawning were cultured under two different rearing systems: intensive (100 eggs l^?1) in 2000 l and semi‐intensive (mesocosm) system (5 eggs l^?1) in 40 000 l conico‐cylindrical tanks. Fish samples were periodically collected along the development from hatching to juveniles at 95 days post hatching (dph). Osteological development, meristic counts and the presence of skeletal deformities were evaluated. Despite the external appearance of the juveniles being similar to wild standards, X‐ray studies revealed a high number of fish (semi‐intensive: 37·8%; intensive: 45·5%) with skeletal deformities. Regardless of the rearing system, no significant interaction was found between the per cent of the most common deformities, axial deviations (lordosis and presence of fused vertebrae). Cranial deformities and kyphosis incidences, however, were significantly higher in intensively cultured P. pagrus. Also, the fused vertebrae in these fish were located mainly in the caudal area instead of pre‐haemal area for semi‐intensively reared P. pagrus. Moreover, a significant interaction was found between the total number of vertebrae and the type of rearing system used; fish from the intensive system showing a higher number of fish with an extra vertebrae (10 abdominal + 15 caudal). Present results suggest a relationship among feeding sequence, osteological development and deformity incidence and location in P. pagrus larvae.     

Effects of ambient colour on colour preference and growth of juvenile rainbow trout Oncorhynchus mykiss (Walbaum)

Colour preference of individual juvenile rainbow trout Oncorhynchus mykiss was tested at 1 and 12° C, and also at 12° C after a 42 day growth experiment under white, blue, green, yellow or red ambient colour. All experiments were carried out under controlled laboratory conditions and the preference was assessed by the location of the fish in a preference tank with four chambers. Rainbow trout showed a preference for blue and green at 1° C and for green at 12° C. After the growth experiment the fish reared in blue tanks preferred blue and green but green was the most preferred colour for the fish reared in green, yellow and red tanks. Yellow and especially red chambers were avoided, irrespective of the ambient colour during the growth trial. The final mass of fish reared in the red aquaria was significantly smaller than that of the fish in green tanks. In addition, when the data of the preference tests were correlated with the data of the growth experiment using mean values of the four tested colours, a very good linear relationship was observed between the preference ( i.e. visit frequency in coloured compartments) and growth rate as well as food intake. When considering the results both from the preference and growth trials it is suggested that green is the best environmental colour for rearing juvenile rainbow trout while rearing in a red environment cannot be recommended.     

Occurrence of Flavobacterium psychrophilum in fish-farming environments

Occurrence of Flavobacterium psychrophilum in fish farms and fish-farming environments was studied using agar plate cultivation, the immunoflourescence antibody technique (IFAT) and nested PCR. Characteristics of 64 F. psychrophilum isolates from rainbow trout Oncorhynchus mykiss, fish farm rearing water, ovarian fluid and wild fish were serotyped, ribotyped and compared biochemically. Virulence of F. psychrophilum isolates from different sources was compared by injection into rainbow trout. Additionally, the number of F. psychrophilum cells shed by naturally infected rainbow trout was determined. F. psychrophilum was detected and isolated from skin mucus, skin lesions and internal organs of diseased rainbow trout and from fish without clinical disease. The pathogen was also present in wild perch Perca fluviatilis, roach Rutilus rutilus, and ovarian fluids of farmed rainbow trout brood fish. Isolates were biochemically homogenous, excluding the capability to degrade elastin. Five different agglutination patterns with different antisera against F. psychrophilum were found among the isolates studied. Although several different ribopatterns were found (ClaI: 12 ribopatterns and HaeIII: 9 ribopatterns), ribotype A was the most dominant. Farmed rainbow trout brood fish carried a broad-spectrum of serologically and genetically different F. psychrophilum in ovarian fluids. Virulence of the tested isolates in rainbow trout varied and naturally infected rainbow trout shed 10(4) to 10(8) cells fish(-1) h(-1) of F. psychrophilum into the surrounding water.     

Impacts of freshwater aquaculture on fish communities: A whole‐ecosystem experimental approach

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Magnetic field perception in the Rainbow Trout, <Emphasis Type="Italic">Oncorhynchus</Emphasis> <Emphasis Type="Italic">mykiss</Emphasis>

In this study, we present evidence for the perception of different magnetic field parameters in a facultative anadromous fish species of the family Salmonidae. Magnetic field perception of the rainbow trout, Oncorhynchus mykiss, was demonstrated with a heartbeat conditioning test. The electrocardiogram was measured with subcutaneously inserted silver wire electrodes in freely swimming fish. We demonstrate a conditioned response (i.e. a significant longer interval between two heartbeats) to an intensity/inclination shift for three adult and two juvenile rainbow trouts. Moreover, a conditioned response to a 90° direction shift was demonstrated for three adult and two juvenile trouts. These findings support the hypothesis that the rainbow trout is able to perceive different magnetic field parameters. Furthermore, the study demonstrates magnetosensation in different developmental stages in the rainbow trout, i.e. juvenile and adult fish.     

Specificity of antibodies established from mammals in rainbow trout (Oncorhynchus mykiss)

This study deals with the question as to whether antibodies established for mammals are also specific for rainbow trout. The reason for this examination is the major economic importance of rainbow trout in aquaculture and the growing scientific attention. However, there are few primary antibodies so far defined for this fish species. Therefore, the aim of the current study was to test the ability of 15 commercially available antibodies for rainbow trout in an indirect immunofluoresence assay to analyse tissue sections of organs. Five commercially available primary antibodies were identified, which were directed against proteins of one or two organs/ cell types in rainbow trout.     

Effects of aquaculture related stressors and nutritional restriction on circulating growth factors (GH, IGF-I and IGF-II) in Atlantic salmon and rainbow trout

The effects of aquaculture related stressors on circulating levels of GH, IGF-I and for the first time, IGF-II in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) were investigated. Specifically, circulating growth factor levels were measured in four different experiments. Two 24 h confinement stressor procedures, (one with Atlantic salmon, the other with rainbow trout); following a hypo-osmotic stressor (freshwater bath) in salt water acclimated, adult, Atlantic salmon; and during a 22 day starvation and re-feeding protocol with juvenile Atlantic salmon. Handling and confinement resulted in significant decreases in circulating levels of all three growth factors in Atlantic salmon, and IGF-I and IGF-II (but not GH) in rainbow trout. A 2-3 h freshwater bath to remove gill parasites on a commercial Atlantic salmon aquaculture operation caused a significant decrease in circulating GH and IGF-I concentrations, but no significant change in IGF-II concentration, 2 days post bathing. Starvation for a period of 15 days in Atlantic salmon resulted in a significant increase in circulating GH levels and a significant decrease in circulating IGF-I and IGF-II. Re-feeding of starved fish for 7 days resulted in a significant decrease in GH to the concentration measured in continually fed fish, however re-feeding did not change plasma levels of IGF-I and IGF-II relative to continually starved fish. The results presented here confirm previously observed handling and confinement stressor induced effects on GH and IGF-I and, for the first time, on IGF-II in salmonids. Furthermore this study confirms the nutritional regulation of GH, IGF-I and IGF-II in juvenile Atlantic salmon.     

Agonistic encounters and cellular angst: social interactions induce heat shock proteins in juvenile salmonid fish

Juvenile salmonid fish readily form dominance hierarchies when faced with limited resources. While these social interactions may result in profound behavioural and physiological stress, it is unknown if this social stress is evident at the level of the cellular stress response—specifically, the induction of stress or heat shock proteins (Hsps). Thus, the goal of our study was to determine if Hsps are induced during hierarchy formation in juvenile rainbow trout (Oncorhynchus mykiss). To this end, we measured levels of three Hsps, Hsp70, Hsc (heat shock cognate)70 and Hsp90 in the white muscle, liver and brain of trout that had been interacting for 36 h, 72 h or 6 days. Our data indicate that Hsps are induced in both dominant and subordinate fish in a time- and tissue-specific manner. In further mechanistic experiments on fasted and cortisol-treated fish, we demonstrated that high plasma cortisol does not affect Hsp induction in trout white muscle or liver, but both conditions may be part of the mechanism for Hsp induction with social stress in the brain. We conclude that the behavioural and physiological stress experienced by juvenile rainbow trout in dominance hierarchies can be extended to the induction of Hsps.