ALBERT

Description: Fütterungsversuche mit Regenbogenforellen zeigen: Magen-Darm-Bakterien von Raubfischen passen sich an vegetarische Nahrung an

Description: Highlights: • First feeding of wild brown trout fry with partial inclusion of dietary plant proteins is beneficial for subsequent growth • Feeding of 50% dietary plant protein results in same growth when compared to fishmeal as exclusive protein source • The early feeding of plant-based diets did not induce nutritional programming effects in first-feeding fry • Wild brown trout fry exhibit highly plastic responses to different feeding strategies during the first months of life • Pepsin and amylase activities are only partly affected by plant-derived protein sources and rather intrinsically regulated Abstract: Decreasing fishmeal availability and increasing prices promote the usage of plant-derived feedstuff as a substitution for fishmeal in commercial salmonid diets. However, little is known about the impact of plant-derived feedstuff on juvenile brown trout (Salmo trutta), a species that exhibits strong phenotypic plasticity with various genetic sub-structures and high overall genetic diversity. Thus, the production of brown trout for restocking purposes preferentially uses wild fish as broodstock to avoid loss of genetic variability. Because of nutritional programming, the strictly carnivorous feeding habit of wild brown trout broodfish could nevertheless have a negative impact on the digestive physiology of fry and fingerlings that are fed with commercial plant-protein containing trout diets. The present study, therefore, investigated whether the feeding of plant-based diets from first feeding onwards induced a permanent improvement in the utilisation of plant-derived protein sources in wild brown trout juveniles. Any plastic responses to the experimental diets resulting in a long-term physiological effect were hypothesised to be not only observed in growth performance, but also in altered pepsin and amylase activities. We demonstrated that (i) the feeding of wild brown trout fry with inclusion levels of up to 50% of dietary plant proteins is beneficial during the first weeks of life and (ii) continuous feeding of at least 50% plant-derived dietary protein resulted in the same rate of growth when compared to the growth resulting from fishmeal as the exclusive dietary protein source. Pepsin and amylase activities were only partly affected by diet-type and it can be concluded that intestinal pepsin and amylase activities in juvenile brown trout are primarily regulated by intrinsic mechanisms. In the present experiment, we were not able to induce a permanent nutritional programming effect of the first feeding diet; instead, a cross-over diet change applied 89 days post first feeding demonstrated that wild brown trout fry exhibit highly plastic responses to different feeding strategies during the first months of life.

Description: Plant-derived protein sources are the most relevant substitutes for fishmeal in aquafeeds. Nevertheless, the effects of plant based diets on the intestinal microbiome especially of juvenile Rainbow trout (Oncorhynchus mykiss) are yet to be fully investigated. The present study demonstrates, based on 16S rDNA bacterial community profiling, that the intestinal microbiome of juvenile Rainbow trout is strongly affected by dietary plant protein inclusion levels. After first feeding of juveniles with either 0%, 50% or 97% of total dietary protein content derived from plants, statistically significant differences of the bacterial gut community for the three diet-types were detected, both at phylum and order level. The microbiome of juvenile fish consisted mainly of the phyla Proteobacteria, Firmicutes, Bacteroidetes, Fusobacteria and Actinobacteria, and thus fits the salmonid core microbiome suggested in previous studies. Dietary plant proteins significantly enhanced the relative abundance of the orders Lactobacillales, Bacillales and Pseudomonadales. Animal proteins in contrast significantly promoted Bacteroidales, Clostridiales, Vibrionales, Fusobacteriales and Alteromonadales. The overall alpha diversity significantly decreased with increasing plant protein inclusion levels and with age of experimental animals. In order to investigate permanent effects of the first feeding diet-type on the early development of the microbiome, a diet change was included in the study after 54 days, but no such effects could be detected. Instead, the microbiome of juvenile trout fry was highly dependent on the actual diet fed at the time of sampling.

Description: Knowledge of the digestive physiology of molluscs is essential for understanding their ecological niches, as well as for their conservation and aquaculture. Freshwater mussels are primarily filter feeders and the complex mechanism of filtration has been studied intensively (Ward et al., 1998; Urrutia et al., 2001; Garrido et al., 2012). However, less is known concerning the physiological mechanisms following ingestion, in particular how food particles are processed in the digestive tract. In bivalves, energy is mostly stored in the form of glycogen, which accounts for 5–14% of the dry weight in Anodonta cygnea (Gäde & Wilps, 1975). For the digestion of various carbohydrates, the crystalline style, a transparent rod composed in part of glycoside hydrolases, is known to be a key component of digestion in the stomach of many snails and marine bivalves. Previous studies (e.g. Alyakrinskaya, 2001) have shown the ability of crystalline style to break down starch in Pseudanodonta complanata and cellulose in Mytilus. Moreover, it has been suggested that crystalline style material not only releases digestive enzymes, but also provides an optimal digestion milieu by buffering ambient pH. Its physiological characteristics, including pH and dissolution, have been described by Hameed (1985) and Warren (1987). This study evaluates the ability of crystalline styles excised from Anodonta anatina to break down different carbohydrate sources and tests the buffering capacity of style material for providing optimal conditions for digestion.

Description: The aim of the present study was to investigate the impact of dietary plant proteins on the gut microbiome of first feeding brown trout (Salmo trutta) reproduced from wild stocks and to evaluate whether the initial microbiome of brown trout fry can be permanently manipulated by the first feeding diet. Therefore, brown trout fry was fed diets based on either 0%, 50% or 90% plant-derived proteins from first feeding onwards and via 16S rRNA gene sequencing a strong dietary influence on the bacterial gut community on phylum and order level was detected. Proteobacteria and Fusobacteria were significantly enhanced when fishmeal was integrated into the experimental diet, whereas plant-derived proteins significantly promoted Firmicutes and Bacteroidetes. In order to evaluate whether the first feeding diet had a permanent effect on the initially established microbial gut community of juvenile brown trout, a cross-over diet-change was applied 61 days post first feeding. 48 days after the diet-change, the gut microbiome of all dietary groups was significantly different from the one initially established after first feeding. Moreover, the first feeding diet had no statistically significant influence on the gut microbiome after the diet-change, demonstrating no permanent effect on the gut microbiome formation.