Does dietary incorporation level of pea protein isolate influence the digestive system morphology in rainbow trout (Oncorhynchus mykiss)?

Growth performance, health status, gut microbiome, and expression of immune and growth-related genes of rainbow trout (Oncorhynchus mykiss) fed diets with pea protein replacement of fish meal

The need for fish meal constrains fish farming and significantly impacts sustainability of the aquaculture industry. Hence, it is important to investigate the use of plant-based protein sources in fish diets. The present study was conducted to determine the effects of different levels of fish meal (FM) replacement by pea protein (PP) in a 60-day feeding experiment in rainbow trout, Oncorhynchus mykiss. Effects on growth performance, body composition, hematology, serum biochemistry and immunology, and immune (TNF-α, IL1-ß and Il-8) and growth-related (GH and IGFI) gene expression were investigated. Five experimental diets (45% protein and 20% lipid) differed in replacement level of FM by PP at rates of 0% (control (PP0)), 25% (PP25), 50%(PP50), 75%(PP75) and 100%(PP100). Fish were fed with experimental diets in triplicate twice daily. The best growth performance was obtained in PP0 and PP25 groups. While fat ratios of fish fillets significantly differed (p < 0.05), there was no significant effects on protein ratios (p < 0.05). There was no significant change in the hematological values of fish, except those fed the PP100 diets, which displayed a reduction in eyrthocyte counts, hemoglobin content and hematocrit. As PP supplementation increased fish showed elevated serum glucose, total protein, cholesterol and myeloperoxidase activity and decreased glutamic pyruvic transaminase and alkaline phosphatase activity. Fish fed diets with between 25 and 75% replacement showed a decline in lactic acid bacteria in the gut. Significant increases in expression were observed in the liver of the PP25 fish relative to the 0% control for all immune and growth-related genes except for IL1-ß. These data suggest that up to 25% of FM can be replaced by PP without any adverse effects on rainbow trout.

Gill arch and raker morphology of common carp (Cyprinus carpio, Linnaeus, 1758) sampled in aquaculture system

The study aimed to investigate the morphologic aspects of common carp's gill arch and gill rakers (Cyprinus carpio, Linnaeus, 1758), an omnivore and highest-produced aquaculture species. The study used 10 common carp (395.35 ± 45.06 g) grown entirely under aquaculture conditions. The fish tissues were fixed with Glutaraldehyde (2.5%) for scanning electron microscopy and with formalin (10%) for stereomicroscopic examination. In the SEM examination, two types of taste papillae (Type II and Type III) were observed in the pharyngeal mucosa. Microridge-like structures in the epithelial layer were found to have two forms. The study findings indicate a significant decrease in gill arch lengths from cranial to caudal and a significant increase in rakers per unit area, as determined through digital calliper measurements and stereomicroscopic examinations (p < 0.05). However, there was no significant difference in measurements of gill arches and raker numbers between the bilateral symmetry of the gill arches (p > 0.05). In conclusion, it was observed that the epithelial structure on the common carp gill arch contained two types of microridge-like structures: the gill arch length decreased from cranial to caudal, and the rake density on these arches increased caudally.

Dietary effect of grape (Vitis vinifera) seed extract mitigates hepatic disorders caused by oxidized fish oil in rainbow trout (Oncorhynchus mykiss)

The major goal of this study was to determine the effect of grape seed extract (GSE) on liver damage in rainbow trout (Oncorhynchus mykiss) that was caused by the consumption of dietary oxidized fish oil (OFO). Rainbow trout were fed six different experimental diets coded OX-GSE 0 (OFO diet), OX-GSE 1 (OFO and 0.1% GSE), OX-GSE 3 (OFO and 0.3% GSE), GSE 0 (fresh fish oil and 0.0% GSE), GSE 1 (fresh fish oil and 0.1% GSE), and GSE 3 (fresh fish oil and 0.3% GSE) for 30 days. The lowest % hepatosomatic index (HSI) result was calculated in fish fed with OX-GSE 0 and the highest HSI was determined in fish fed with GSE 1 diets (p < 0.05). Histopathologically, hydropic degeneration in hepatocytes significantly increased OX-GSE 0 and GSE 3 compared to GSE 1 diets (p < 0.05). Deposition of lipid droplets in hepatocytes was significantly increased in OX-GSE 0 and OX-GSE 3 groups than others (p < 0.05). Liver biochemistry parameters such as superoxide dismutase (SOD), glutathione (GSH), and malondialdehyde (MDA) were significantly affected by OX and GSE treatments (p < 0.05). There were significant differences in alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) among the liver enzymes analyzed in serum in OX and GSE (p < 0.05), meanwhile no difference was observed in lactate dehydrogenase (LDH) values between groups (p > 0.05). In conclusion, liver biochemistry and histopathology of rainbow trout consuming diets containing oxidized fish oil were negatively affected. However, it was determined that the supplementation of 0.1% GSE to the diet had a significant ameliorative role in these adverse effects.

Black soldier fly full-fat meal in Atlantic salmon nutrition – Part A: Effects on growth performance, feed utilization, selected nutriphysiological traits and production sustainability in fries

Black soldier fly larva meal (BSFM) application as an innovative feed material has been developed in aquaculture nutrition. However, recent scientific literature is still lacking in the case of insect meal effects on different stages of salmonid fish, and the vast majority of research is focused on farmed Atlantic salmon. Therefore, the holistic approach was undertaken in the cycle of two studies carried out: on fries and pre-smolts. This study aimed to evaluate the effect of fish meal (FM) replacement by full-fat BSFM in Atlantic salmon fry diets on the growth performance, feed utilization, crude protein and crude fat digestibility, somatic indices, histomorphology of intestines, and environmental sustainability. Additionally, pellet quality was assessed. Two experiments were performed on 360 Atlantic salmon fries – each of which lasted 60 days. For the first experiment, 240 individuals were distributed to four experimental groups: six replicates (tanks) per group and 10 fish per tank. For the second experiment, 120 individuals were distributed to four experimental groups: three replicates (tanks) per group and 10 fish per tank were used. The following groups were applied: CON – without the addition of full-fat BSFM and with 39% FM; BSFM5 – with 5% addition of full-fat BSFM and 36.1% FM; BSFM10 – with 10% full-fat BSFM and 33.3% FM; BSFM15 – with 15% addition of full-fat BSFM and 30.3% FM. The present study showed satisfactory results of BSFM inclusion at the levels of 5% and 10% as a replacement for fish meal in feeds for Atlantic salmon fries. No negative effects on growth performance, feed utilization, protein and fat digestibility, or intestinal structure were recorded. Simultaneously, insect meal inclusion in Atlantic salmon diets significantly improved the environmental sustainability of the feed. In the case of BSFM15, decreases in body weight gain, protein lipid efficiency ratio, and lipid efficiency ratio, as well as increases in feed conversion ratio, were observed. Therefore, the use of shares higher than 10% of BSFM in Atlantic salmon fries may not be recommended.

Temporal variations in hematological, immunological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss) acclimated to high-saline water in the Northern Aegean Sea

The present study evaluated the health status of rainbow trout (30.24±5.34 g) acclimated to high-saline water (28‰). Among adaptation procedures, gradually-acclimated (for 48 h) fish showed best performance, which were then introduced to the offshore cage-farm for further monitoring of fish health in marine environment over a long-term period of 100 days, until harvest weight of 319.9±48.51 g. Fish health and welfare was evaluated by means of biochemical parameters (viscerasomatic index, hepatosomatic index, mesenteric fat index, and spleen somatic index), hematological parameters (serum glucose, triglyceride, cholesterol, total protein, albumin, globulin), and immune parameters (lysozyme, myeloperoxidase, respiratory burst and potential killing values). Gradual acclimation to high-saline water did not show any adverse effects on health parameters. No significant differences were found in biometric measures (P>0.05). However, a time-dependent increase was recorded in hematology markers (P<0.05) after seawater transfer, and the health status improved over long-term from March 7 to June 14, 2018. All serum biochemical markers, except the total protein showed significant alterations (P<0.05) in long-term but without detrimental influence by day-100. Therefore, it seems possible to expand trout farms from brackish water sites to higher saline environments up to 28‰ salinity, with no detrimental impacts on fish health, that in turns may significantly contribute to the extension of potential aquaculture sites to wider areas.

How potentially sustainable solutions may be unsustainable in practice: carrot pomaces in common carp nutrition

The aim of this study was to evaluate the effects of carrot pomaces dried at two temperatures as a feed component on growth performance, environmental sustainability, and meat quality in common carp (Cyprinus carpio). Three diets were developed: a control without pomace (CON); CPL with 15.5% carrot pomace dried at 40°C and CPH with 23.6% carrot pomace dried at 120°C. A total of 240 two-year-old common carp (average body weight of individual: 1025 g) were randomly distributed into 12 tanks, four per treatment, including 20 fish per tank. The experiment was performed using an outdoor open flow aquaculture system. The growth trial lasted 60 days, after which fish samples were taken for analysis of meat quality parameters. There were no significant differences between groups in terms of the final body weight, protein efficiency ratio, or survival rate. However, in terms of weight gain, specific growth rate, and feed conversion ratio, fish fed the CPH diet exhibited significant worsening. Moreover, the fillets of fish from the CPH group exhibited a darker coloration compared to the CON diet. It is concluded that high temperature drying of carrot pomace added to carp diet negatively affected fish quality. It should be also emphasized that inclusion of the both carrot pomaces tested in this study significantly increased the usage of fish meal per kilogram of fish body weight gain. These results showed a reduced efficacy of using carrot pomace in practical and sustainable common carp nutrition.