Broodstock nutritional programming improves the offspring utilization of plant-based diets in gilthead sea bream through changes in hepatic metabolism. Attention was initially focused on fatty acid ...desaturases, but it can involve a wide range of processes that remain largely unexplored. How all this can be driven by a different genetic background is hardly underlined, and the present study aimed to assess how broodstock nutrition affects differentially the transcriptome and genome-wide DNA methylome of reference and genetically selected fish within the PROGENSAR selection program. After the stimulus phase with a low fish oil diet, two offspring subsets of each genetic background received a control or a FUTURE-based diet. This highlighted a different hepatic transcriptome (RNA-seq) and genome-wide DNA methylation (MBD-seq) pattern depending on the genetic background. The number of differentially expressed transcripts following the challenge phase varied from 323 in reference fish to 2,009 in genetically selected fish. The number of discriminant transcripts, and associated enriched functions, were also markedly higher in selected fish. Moreover, correlation analysis depicted a hyper-methylated and down-regulated gene expression state in selected fish with the FUTURE diet, whereas the opposite pattern appeared in reference fish. After filtering for highly represented functions in selected fish, 115 epigenetic markers were retrieved in this group. Among them, lipid metabolism genes (23) were the most reactive following ordering by fold-change in expression, rendering a final list of 10 top markers with a key role on hepatic lipogenesis and fatty acid metabolism (cd36, pitpna, cidea, fasn, g6pd, lipt1, scd1a, acsbg2, acsl14, acsbg2). Gene expression profiles and methylation signatures were dependent on genetic background in our experimental model. Such assumption affected the magnitude, but also the type and direction of change. Thus, the resulting epigenetic clock of reference fish might depict an older phenotype with a lower methylation for the epigenetically responsive genes with a negative methylation-expression pattern. Therefore, epigenetic markers will be specific of each genetic lineage, serving the broodstock programming in our selected fish to prevent and mitigate later in life the risk of hepatic steatosis through changes in hepatic lipogenesis and fatty acid metabolism.
The aquaculture industry depends upon the development of sustainable protein sources to replace fishmeal (FM) in aquafeeds and the products derived from soybeans are some of the most studied plant ...feedstuffs. A key area of investigation for continuing to improve modern aquafeeds includes the evaluation of varying proportions and combinations of plant ingredients to identify mixtures that are more efficiently utilized by the fish. This study investigated the effects of increasing soybean meal (SBM) by replacing a mix of plant ingredients in low FM (20%) diets on growth, blood biochemistry profile and gut histology on European sea bass. Five isonitrogenous and isolipidic experimental diets were formulated: four diets containing increasing SBM levels (0, 10, 20 and 30%; 0SBM, 10SBM, 20SBM and 30SBM, respectively) with a low content of FM (20%) and one control diet (0% SBM; 35% FM). Diets containing SBM brought to comparable performance and protein utilization, while 0SBM had negative impact on feed conversion rate and protein utilization. Blood parameters suggested an optimal nutritional status under all feeding treatments, even though slightly decreased values were reported at increasing dietary SBM. Histology examination did not show any changes indicative of soy-induced enteritis. We can conclude that for European sea bass: (i) different blends of plant protein did not affect feed intake despite the 20% FM dietary level; (ii) the inclusion of SBM maintains optimal growth and feed utilization in low FM diets; (iii) blood biochemistry profile showed a good nutritional status under all feeding regimes; (iv) no evidence of soy-induced enteritis was reported in any group fed low FM diets. For formulation of practical diets in on-growing of European sea bass, SBM up to 30% can be successfully incorporated into feeds containing low FM inclusion.
To understand the effect of low dietary phosphorus (P) intake on the vertebral column of Atlantic salmon Salmo salar, a primary P deficiency was induced in post‐smolts. The dietary P provision was ...reduced by 50% for a period of 10 weeks under controlled conditions. The animal's skeleton was subsequently analysed by radiology, histological examination, histochemical detection of minerals in bones and scales and chemical mineral analysis. This is the first account of how a primary P deficiency affects the skeleton in S. salar at the cellular and at the micro‐anatomical level. Animals that received the P‐deficient diet displayed known signs of P deficiency including reduced growth and soft, pliable opercula. Bone and scale mineral content decreased by c. 50%. On radiographs, vertebral bodies appear small, undersized and with enlarged intervertebral spaces. Contrary to the X‐ray‐based diagnosis, the histological examination revealed that vertebral bodies had a regular size and regular internal bone structures; intervertebral spaces were not enlarged. Bone matrix formation was continuous and uninterrupted, albeit without traces of mineralization. Likewise, scale growth continues with regular annuli formation, but new scale matrix remains without minerals. The 10 week long experiment generated a homogeneous osteomalacia of vertebral bodies without apparent induction of skeletal malformations. The experiment shows that bone formation and bone mineralization are, to a large degree, independent processes in the fish examined. Therefore, a deficit in mineralization must not be the only cause of the alterations of the vertebral bone structure observed in farmed S. salar. It is discussed how the observed uncoupling of bone formation and mineralization helps to better diagnose, understand and prevent P deficiency‐related malformations in farmed S. salar.
The aim of the present study was to combine maximum replacement of fish meal and fish oil with plant ingredients in feed for Atlantic salmon, in order to gain a sound and sustainable net fish protein ...production. The design implied that all known nutrient requirements should be met. Atlantic salmon smolts with an initial weight of 0.3 kg were fed in triplicate either a fully marine control diet or one of three plant based diets through the seawater production phase for 12 months, until final weight of approximately 4 kg. In a maximum plant based diet, 80% of the fish meal was replaced with a mixture of plant protein ingredients and krill meal, while 70% the fish oil was replaced with a mixture of vegetable oils. Two intermediate replacement diets contained either one half of this fish meal replacement level and maximum fish oil replacement, or one half replacement level of fish oil and maximum fish meal replacement. Fish performance was assessed by measuring mortality, feed intake, growth, nutrient digestibility and nutrient utilisation. Specific growth rate was significantly lower in the combined high replacement group compared to the other experimental groups, both for the first 3-month period (12%) and for the complete 12 months (9%) of feeding. The final fish weights were 17% lower in the combined high replacement group and 9% lower in the high plant protein and intermediate vegetable oil group, compared to the marine control and the intermediate plant protein group. Significantly reduced feed intake during the first period and slightly reduced digestibility of 16:0 and starch were identified as possible causes for growth depression, since minor differences in protein or lipid digestibility, feed conversion ratio, and protein and lipid retention were observed.
The maximum fish meal and fish oil replacement represented a net production of fish protein, with 2 kg salmon protein produced per kg fish meal protein fed. This being four-fold more efficient usage of fish meal in the 80% plant protein diets compared to the 100% fish raw material diet.
The aim of the present study was to investigate the cataract preventive effect of dietary histidine regimes in adult Atlantic salmon (Salmo salar L.) in seawater, both through manipulating the ...dietary histidine level and feeding period. Mean body weight of individually tagged Atlantic salmon at the start of the experiment was 1662 (sd 333) g. Low prevalence of mild cataracts were recorded in the beginning of June. Three fishmeal and fish oil-based extruded diets (crude protein: 375 g/kg and fat: 342 g/kg), differing only in histidine content (low (L): 9·3, medium (M): 12·8 and high (H): 17·2 g histidine/kg diets), were fed to duplicate net pens in seawater. The experimental period was divided into three seasons (June–July; July–September; September–October), each starting and ending with individual cataract examination, assessment of somatic data, and sampling of lens and muscle tissues for analysis of histidine and histidine derivatives. In July and September, a part of the population fed L- and H-histidine feeds were transferred (crossed over) to respective series of replicate net pens fed L-, M- and H-histidine diets (i.e. eleven experimental feeding groups at trial conclusion). The fish doubled their body weight from June to October, with no systematic effects on weight gain of dietary histidine feeding regimes. Development of severe cataracts was observed between July and September. The cataract severity was directly related to the dietary histidine level fed during the first and second periods. Feeding histidine-supplemented diets (M or H) in the first period from June to July mitigated later cataract outbreaks. The status of selected free imidazoles in muscle and lens tissues reflected the dietary histidine feeding regimes, relative to both feed concentration and feeding duration. The study shows the risk for cataract development for adult Atlantic salmon, 1 year after the transfer of salmon smolts from freshwater to seawater, which to a major extent can be prevented by histidine supplementation just before and during the early phase of cataract development.
Gilthead seabream (Sparus aurata Linnaeus, 1758 (Perciformes, Sparidae)) is an important aquaculture species in the Mediterranean Sea basin. Yet, quantitative data on its dentition under standard ...farming conditions are currently lacking. Furthermore, it is unknown if the dentition can adapt to food of different sizes. Here, we describe the lower jaw dentition of juvenile S. aurata fed a standard pellet size (4 mm) and present a detailed analysis of 11 representative teeth. Overall, the number of teeth showed large individual variation, but it was not significantly related to fish length. Considerable left–right differences were observed, without clear side dominance. We also assessed the influence of feeding S. aurata a smaller (2 mm) or larger (6 mm) pellet size. Four months of feeding with different pellet sizes did not cause detectable differences in total tooth number on the dentaries at the time of harvest, nor in size of the teeth assumed to be most relevant in food processing. If and how different pellet sizes may nevertheless affect digestion, and eventually fish health, is subject for further studies.
The present study aimed at determining the effect of re-esterified oils with different monoacylglycerol (MAG) content, produced from two different vegetable sources with different degrees of ...saturation, palm and rapeseed, on fatty acid digestibility in rainbow trout. Re-esterified oils were obtained from a chemical esterification process using acid oils (free fatty acids (FFA)-rich by-products from the refining of vegetable oils) and glycerol (by-product of biodiesel production). This process, which produces the formation of triacylglycerols (TAG), reduces the content of FFA present in the acid oil and generates a redistribution of the fatty acids in the glycerol molecule. This redistribution could increase the amount of saturated fatty acids (SFA) located at the sn-2 position of acylglycerols. Moreover, it allows obtaining fats with a certain proportion of MAG, known for being good emulsifiers. Therefore, a higher nutritive value of re-esterified oils than that of acid oils might be expected. A 21-day feeding trial where triplicate groups of rainbow trout were fed nine experimental diets formulated to contain a 21% of different experimental oils was carried out. For each source, four different types of oil were used: native, re-esterified low in MAG, re-esterified high in MAG and acid. A commercial fish oil was used for the control diet. Although re-esterified oils had better apparent digestibility coefficients (ADC) of SFA than their corresponding acid oil diets, no improvement in SFA digestibility was observed in rainbow trout fed re-esterified oils diets compared to those fed native oil diets, not even when a high content of MAG was present. Although this improvement did not occur, both palm and rapeseed re-esterified oils could be incorporated as a fat source in diets for rainbow trout without negatively affecting fatty acid digestibility values. The study concluded that fatty acid digestibility in the experimental oils was more affected by their degree of saturation than by their positional distribution and lipid class composition of the oils.
•It was the first time re-esterified vegetable oils were used as an ingredient in fish diets.•Re-esterification involves the use of a waste vegetal product and the application of commercial chemical technique.•Re-esterified vegetable oils could be a sustainable and suitable alternative to vegetable oils as a fat source for fish diets.•Fatty acid digestibility was more affected by the degree of saturation than by the positional distribution and lipid class.
The present study was carried out to investigate whether the dietary histidine requirement to reduce cataract development is higher than that for growth in Atlantic salmon smolts (Salmo salar L.) ...after seawater transfer and whether dietary vegetable oils contribute to cataractogenesis. Duplicate groups of salmon smolts were fed ten experimental diets with either fish oil (FO) or a vegetable oil (VO) mix replacing 70 % FO and histidine at five target levels (10, 12, 14, 16 and 18 g His/kg diet) for 13 weeks after seawater transfer. The VO diet-fed fish exhibited somewhat inferior growth and feed intakes compared with the FO diet-fed fish, irrespective of the dietary histidine concentration. Both cataract prevalence and severity were negatively correlated with the dietary histidine concentration, while lens N-acetyl-histidine (NAH) concentrations were positively correlated with it. The fatty acid profiles of muscle, heart and lens reflected that of the dietary oils to a descending degree and did not affect the observed cataract development. Muscle, heart and brain histidine concentrations reflected dietary histidine concentrations, while the corresponding tissue imidazole (anserine, carnosine and NAH) concentrations appeared to saturate differently with time. The expression level of liver histidase was not affected by the dietary histidine concentration, while the liver antioxidant response was affected in the VO diet-fed fish on a transcriptional level. The lowest severity of cataracts could be achieved by feeding 13·4 g His/kg feed, independently of the dietary lipid source. However, the present study also suggests that the dietary histidine requirement to minimise the risk of cataract development is 14·4 g His/kg feed.
The present study compared the effects of diets formulated with reduced fishmeal (FM) content and either 100% fish oil (FO) or 100% of a vegetable oil (VO) blend in post-smolts of three family groups ...of Atlantic salmon. Two groups were selected as being either “Lean” or “Fat” based on estimated breeding values (EBV) for flesh adiposity of their parents derived from a breeding programme, while the third group (CAL) was a mix of non-pedigreed commercial families unrelated to the two groups above. The VO blend comprised rapeseed, palm and a new product,
Camelina oil in a ratio of 5/3/2, and diets were fed to duplicate pens of each salmon group. After an ongrowing period of 55
weeks, to reach a mean weight of 3
kg, the fish from all treatments were switched to a decontaminated FO for a further 24
weeks to follow restoration of long-chain
n−3 polyunsaturated fatty acids (LC-PUFA) in the fish previously fed VO. Final weights were significantly affected by family group and there was also an interaction between diet and group with Fat and Lean FO fish being larger than the same fish fed VO. Specific growth rate (SGR) was highest in CAL fish (1.01), feed conversion ratio (FCR) was highest in the Lean fish but there were no significant effects on thermal growth coefficient (TGC). Condition Factor (CF) was lowest in CAL fish while the hepato-somatic index (HSI) was highest in Lean fish and viscero-somatic index (VSI) highest in Fat fish. Flesh and viscera lipid content was affected by both family group and diet with a significant interaction between the two. Flesh lipid in fish fed FO was in the order Fat
>
CAL
>
Lean although this order was Fat
=
Lean
>
CAL when fed VO. Flesh fatty acid compositions were affected mainly by diet although some minor fatty acids were also influenced by group. Fish fed VO had
n−3 LC-PUFA reduced by ∼
65% compared to fish fed FO but this could be restored by a 16-week FO finishing diet phase. The differences observed in lipid and fatty acid deposition suggested that genetics affected lipid deposition and metabolism and that breeding programmes could select for fish that retained more
n−3 LC-PUFA in their flesh, particularly when fed diets low in these fatty acids.
Re‐esterified vegetable oils are obtained from a chemical esterification reaction between vegetable acid oils and glycerol. Due to their properties, it is expected that they have a higher nutritive ...value than their corresponding acid oils and a better digestibility than their native counterparts. The aim of this study was to determine the effect of re‐esterified oils with a different monoacylglycerol (MAG) and diacylglycerol (DAG) content, produced from palm or rapeseed, on fatty acid digestibility in gilthead sea bream (Sparus aurata). Triplicate groups of fish were fed nine experimental diets containing different oils during 28 days. For each source, four different types of oil were used: native, re‐esterified low or high in MAG and DAG and acid. A commercial fish oil was used for the control diet. Diets containing re‐esterified oils had better apparent digestibility coefficients (ADC) of total fatty acids than acid oil diets. Re‐esterified oils do not negatively affect apparent digestibility coefficients of fatty acids when compared to their corresponding native oils and could be incorporated as a source of energy in diets for gilthead sea bream. An improvement in digestibility compared to the native oil diet was only obtained in palm re‐esterified oil high in MAG and DAG.
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