Jaume Pérez-Sánchez

Protein growth performance, amino acid utilisation and somatotropic axis responsiveness to fish meal replacement by plant protein sources in gilthead sea bream (Sparus aurata)

Partial or total replacement of fish meal by a mixture of plant protein sources (corn gluten meal, wheat gluten, extruded peas, rapeseed meal) balanced with indispensable amino acids (IAA) was examined in juvenile gilthead sea bream (Sparus aurata) over the course of a 12-week growth trial. A diet with fish meal (FM) as the sole protein source was compared to diets with 50%, 75% and 100% of replacement (PP50, PP75, PP100). Protein retention was improved with more plant protein supply, and just a slight decrease in the final weight gain was found in fish fed PP50 and PP75 diets. However, in the PP100 group, weight gain was depressed up to 30% mainly as the result of a marked reduction of feed intake. These fish also showed a lower fat gain along with a marked hypocholesterolemic effect. Dietary treatment did not alter the hepatic activity of amino acid catabolising enzymes (alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), glutamate dehydrogenase (GDH)), although the size of the total muscle free amino acid (FAA) pool was increased by more plant protein supply. The activity of the somatotropic axis also varied among experimental groups, and the up-regulation of circulating growth hormone (GH) levels with a high plant protein supply followed the decrease in growth rates, plasma levels of insulin-like growth factor-I (IGF-I), and liver mRNA transcripts of IGF-I and GH receptors. This catabolic feature evidenced a liver desensitisation to the anabolic action of GH in the PP100 group, and to a lesser extent in the PP75 group. Taken together all these findings, up to 50-75% of fish meal replacement seems to be feasible with IAA supplementation, but further research is needed to fully identify the responsible factors for the depressed feed intake in order to achieve a full replacement in a fish species having high dietary protein requirements.

Growth performance and adiposity in gilthead sea bream (Sparus aurata): risks and benefits of high energy diets

A factorial experiment was conducted for 7 weeks over the summer period (23–26°C) with gilthead sea bream fingerlings fed under restricted (1–1.75%) and unrestricted (2.5–3%) conditions with two practical diets (55% protein–9% lipid; 46% protein–17% lipid). Specific growth rates ranged from 0.65 to 2.3%, and no significant differences were found at a given feeding level between dietary treatments. At the highest feeding level, no significant differences in the viscerosomatic, hepatosomatic and mesenteric fat index were observed, although the daily fat gain was always higher in fish fed the 17% lipid diet. Under restricted feeding conditions, no significant differences in daily N gain were found. However, in fish fed to visual satiety, N gain was significantly lower in fish fed the lipid enriched- diet. Thus, when considering protein retention, a reliable protein sparing effect of dietary lipid was only found under restricted feeding conditions, where a feed gain ratio near to 1 was found with both diets at the intermediate ration size (1.75%). Plasma growth hormone (GH) levels decreased with the increase of ration size. Besides, under fixed feeding levels, plasma GH levels were lower in fish fed the high lipid diet. An opposite trend was found in fish fed to satiety. After 8 days of fasting, fish previously fed the 17% lipid diet to satiety also exhibited a more pronounced hypersomatotropism and hypoglycemia, linked to increased loss of body fat. As a practical consequence, when high fat diets are used, these findings show the need to optimize ration size to avoid unwanted adiposity and impaired growth performance in gilthead sea bream.

Endocrine mediators of seasonal growth in gilthead sea bream (Sparus aurata): the growth hormone and somatolactin paradigm

Regulation of somatolactin (SL) and the somatotropic axis was examined year-around at three different stocking times (spring, summer, and autumn) in a Mediterranean fish, the gilthead sea bream (Sparus aurata). The overall timing of plasma growth hormone (GH) increase was similar among trials (late spring-early summer), but the range of variation year-around was different and followed changes in food intake. Total plasma insulin-like growth factor-I primarily followed changes on growth rates, and a close positive correlation between IGF-I and thermal-unit growth coefficient (TGC) was found irrespective of fish stocking time. Thus, the activation of the somatotropic axis preceded always warm growth spurts, whereas the rise of SL in concurrence with low plasma cortisol levels was found at late autumn. This up-regulation of circulating SL titres preceded the winter inhibition of feeding, and it was more severe in big fish (spring and summer stocking times) than in small fish (autumn stocking time), growing with a relative high efficiency during the cold season despite of a severe hypertriglyceridemia and a high hepatosomatic index. These new insights provide good evidence for a different timing of GH and SL increases, and it is likely that the dominant role of SL in energy homeostasis is to be a mediator of the adaptation to fasting after replenishment of body fat stores, whereas GH and IGF-I are perceived as growth-promoting signals in times of food intake and increasing temperature and day-length.

Effects of dietary amino acid profile on growth performance, key metabolic enzymes and somatotropic axis responsiveness of gilthead sea bream (Sparus aurata)

Abstract Juvenile gilthead sea bream were fed to visual satiety with isonitrogenous diets based on fish meal and different plant ingredients (33–35% replacement) supplemented with free amino acids to meet the desired indispensable amino acid (IAA) profile and dispensable amino acid (DAA) content. In diets M and WB, IAA profile and DAA content resemble that of the muscle or whole body, respectively. In diets MGlu and WBGlu, DAA content was increased by adding l -glutamic acid (Glu) and thus the IAA/DAA ratio varied from 1.13 (diet M) to 0.80 (diet WBGlu). Growth rates were not significantly different among experimental groups, but feed conversion ratio and nitrogen retention were impaired by the decrease of dietary IAA/DAA ratio. Postprandial ammonia excretion increased with the increase of dietary DAA content irrespective of IAA profile. Conversely, hepatic activity of glutamate dehydrogenase (GDH) was lower in fish fed diet WBGlu than in fish fed diet M. Hepatic growth hormone (GH) binding was not significantly affected by the dietary treatment, but circulating levels of insulin-like growth factor-I (IGF-I) and GH were, respectively, down- and up-regulated in fish fed diet WBGlu, which suggests some defect in the transmission of GH receptor signal. Fat retention and hepatic activities of lipogenic enzymes (glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME) were decreased in fish fed diet MGlu. Key metabolic enzymes of hepatic glycolysis (glucokinase, GK) and gluconeogenesis (phosphoenolpyruvate carboxykinase, PEPCK) were also altered in this group of fish. Since soybean meal concentration was highest in diet MGlu, results on lipid and carbohydrate metabolism can be primarily attributed to this component of the diet. In contrast, data on growth performance, ammonia excretion and GH axis mainly reflect changes in the dietary amino acid profile, which reveals that a muscle IAA profile and a high IAA/DAA ratio are important in feeds for gilthead sea bream.

Growth hormone axis as marker of nutritional status and growth performance in fish

The endocrine control of growth and metabolism is interrelated and many of the endocrine factors involved in the regulation of lipid and protein metabolism are also involved in nutrient utilization, immune system function and somatic growth. All these processes are impaired in catabolic states induced by fasting, protein deprivation and chronic liver diseases as a response to the consequential changes in the endocrine system. In this regard, it must be noted that concentrations of circulating metabolites may be quite different depending on the catabolic state. However, in all the metabolic disorders that shared an increased catabolism/anabolism balance, plasma insulin levels are depressed, whereas those of GH are elevated. This hypersomatotropism, linked to growth retardation, is accompanied by a reduction of plasma IGF-I concentration, which reflects some refractoriness of liver to the anabolic action of GH. Changes in GH availability and liver GH-responsiveness can also be established as a function of age, fish species, and environmental factors (photoperiod and temperature). In the present work, the regulation and mode of GH action is discussed in order to provide a useful tool to assess the nutritional status and growth performance of cultured fish.

High levels of vegetable oils in plant protein-rich diets fed to gilthead sea bream ( Sparus aurata L.): growth performance, muscle fatty acid profiles and histological alterations of target tissues

The feasibility of fish oil (FO) replacement by vegetable oils (VO) was investigated in gilthead sea bream (Sparus aurata L.) in a growth trial conducted for the duration of 8 months. Four isolipidic and isoproteic diets rich in plant proteins were supplemented with L-lysine (0.55 %) and soya lecithin (1 %). Added oil was either FO (control) or a blend of VO, replacing 33 % (33VO diet), 66 % (66VO diet) and 100 % (VO diet) of FO. No detrimental effects on growth performance were found with the partial FO replacement, but feed intake and growth rates were reduced by about 10 % in fish fed the VO diet. The replacement strategy did not damage the intestinal epithelium, and massive accumulation of lipid droplets was not found within enterocytes. All fish showed fatty livers, but signs of lipoid liver disease were only found in fish fed the VO diet. Muscle fatty acid profiles of total lipids reflected the diet composition with a selective incorporation of unsaturated fatty acids in polar lipids. The robustness of the phospholipid fatty acid profile when essential fatty acid requirements were theoretically covered by the diet was evidenced by multivariate principal components analysis in fish fed control, 33VO and 66VO diets.

The involvement of growth hormone in growth regulation, energy homeostasis and immune function in the gilthead sea bream (Sparus aurata [Pagrus aurata]): a short review.

The aim of this mini-review is to provide a comprehensive survey of the physiological role of growth hormone (GH) in the Mediterranean sea bream (Sparus aurata). For this purpose, sea bream GH is now available as a recombinant and bioactive protein in a practically unlimited amount. In juvenile and adult fish, the liver is the most important target for the direct action of GH. Nevertheless, it must be noted that in sea bream larvae the greater concentration of GH-binding sites occurs in the head region, which also exhibits a fast growth. This finding suggests that GH exerts at this early stage of development a direct action on growing tissues rather than a systemic one mediated by hepatic IGF-I. However, the GH-liver axis is later a sensitive marker of growth performance, and seasonal changes in circulating GH levels and hepatic GH-binding are well characterized. The effect of age, water temperature and feeding regimes has also been studied. As a characteristic feature, fasting and malnourished fish show a decrease in hepatic GH-binding and circulating IGF-I, which increases pituitary GH release due to a lack of negative feedback inhibition. Interestingly, the up-regulation of plasma GH levels has also been described in fish fed to visual satiety. This, together with a decreased feed conversion, is more evident in fish fed high energy diets, and it has been suggested that this metabolic derangement is an adaptive response to protect adipose tissue and perhaps other organs and tissues from the excessive lipid deposition, when abundant energy is available. Experimental evidence also indicates that GH is able to exert a direct effect on sea bream erythroid and immunocytes. It is now recognized that GH receptors are present in erythroid, lymphoid and myeloid cells, and both GH and IGF-I have a mitogenic effect. GH also acts as a phagocytic-activating factor, and the presence of GH transcripts in the head kidney has been demonstrated by RT-PCR. All this provides suitable evidence for a pleiotropic and crucial role of GH in a lower vertebrate species such as sea bream.

Protein sparing effect of dietary lipids in common dentex (Dentex dentex): A comparative study with sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

The common dentex (Dentex dentex) is a sparid fish which is considered a suitable candidate for Mediterranean aqua- culture. A seven-weeks feeding trial was conducted over the summer period with common dentex, sea bream (Sparus aurata) and sea bass (Dicentrurchus kzbrax). All three species were fed to visual satiety with two practical diets with varying crude protein and crude fat levels (55 % protein, 9 % lipids; 46 % protein, 17 % lipids). The initial body weights were 8.2, 11.6 and 17.3 g for common dentex, sea bass and sea bream, respectively. In all cases, specific growth rates were not significantly affected by dietary treatment, but they varied among species (sea bass 1.7-1.8 %; sea bream 2.1-2.3 %; common dentex 3.1-3.2 %). When comparisons between fish species were made, we observed that the increase in growth rates was linked to a decrease of the whole body fat content, as a consequence of a greater utilisation of dietary lipids as energy

Fish Growth Hormone Receptor: Molecular Characterization of Two Membrane-Anchored Forms

Abstract A RT-PCR approach was used to clone and sequence the full-length growth hormone receptor (GHR) of a teleost fish, the turbot (Scophthalmus maximus). Total liver RNA was amplified by RT-PCR with degenerate primers designed in extracellular and cytoplasmic regions, and a single DNA fragment of 1100 bp was obtained. The entire coding region was obtained by 5’ and 3’ RACE assays, and comprises an open-reading frame of 633 amino acids. This sequence shows the characteristic motifs of the class I cytokine receptor superfamily, and its amino acid identity with mammalian, avian, reptilian and amphibian GHRs is 32–36%. The 3’ RACE also revealed the occurrence of an alternate messenger encoding a membrane-anchored truncated receptor, which could facilitate the production of GH-binding protein in fish species. This report represents the first data on fish GHR sequence, and it provides evidence for the conservation of this receptor throughout vertebrate evolution.

Somatotropic regulation of fish growth and adiposity: growth hormone (GH) and somatolactin (SL) relationship ☆

Growth hormone (GH) and insulin-like growth factors (IGFs) play a major role in fish development and metabolism, and several studies have allowed discernment of a complex and tissue-specific collection of salmonid IGF-I transcripts (Ea-4, Ea-3, Ea-2, Ea-1), which are the result of the alternative splicing of the E-domain region. However, the pattern of IGF-I expression is different in non-salmonid fish, and only one or two transcripts (Ea-4, Ea-2) have been detected in hepatic and extrahepatic tissues of common carp, barramundi, black sea bream and gilthead sea bream. Despite this, when comparisons are made within Mediterranean fish species (European sea bass, common dentex and gilthead sea bream), plasma IGF-I levels are consistent with fish species differences in growth rates. Changes of growth rates, and plasma IGF-I and GH levels are also found in response to changes in diet composition and ration size, which may serve to assess the suitability of feeding regimes in aquaculture practice. Regulation of plasma somatolactin (SL) levels is also examined in gilthead sea bream, and the resulting plasma SL profile differs from that of GH. Thus, in contrast to GH, plasma SL levels augment with the increase of ration size and fish size (advancement of age). A transient increase in plasma SL levels is also found in short-term fasted fish, and this fish peptide may act as an anti-obesity hormone helping to expedite growth-reproductive processes following replenishment of fat stores, and/or mediate the adaptation to fasting until the lipolytic action of GH and/or other endocrine factors is fully accomplished. This agrees with the known increase of plasma SL levels during acute stress and exhaustive exercise. However, a causal link between SL and energy mobilisation (lipid metabolism) remains to be established, and further research is needed to determine the extent to which SL and GH act in a complementary manner to make available metabolic fuels and to regulate body fat mass and feeding behaviour.