The presence of antinutritional substances, such as phytate, in fish feed affects the digestibility and absorption of minerals and nutrients by fish, while reduced availability of phosphorus (P) in wheat-based feeds used in fish farming can increase pollution in the aquatic environment. Phosphorus digestibility can be effectively increased in aquaculture through the addition of both phytase and citric acid. The aim of our study was to investigate the effects of phytase enzyme and citric acid addition on P digestibility, production parameters and blood parameters in farmed common carp (Cyprinus carpio L.). Two trials were undertaken using the following experimental diets: control with no additives (C), low enzyme content (500 FTU/kg; L), high enzyme content (1,000 FTU/kg; H), low enzyme contents with 3% citric acid (LA), high enzyme contents with 3% citric acid (HA). Initial results showed that LA increased P digestibility by 27% and HA by 26%, with no increase detected using L and H. In the second trial, in which production and blood parameters were examined, use of LA and HA resulted in a 20% decreased feed conversion ratio and 11% higher specific growth rate. Furthermore, acidified diets resulted in an increased blood plasma calcium and inorganic P, without negative effects on any parameter. Addition of phytase and citric acid to C. carpio granulated feeds also has a positive influence on the environment by reducing excreted P.

Disease conditions that involve multiple predisposing or contributing factors, or manifest as low performance and/or low-level mortality, can pose a diagnostic challenge that requires an interdisciplinary approach. Reaching a diagnosis may also be limited by a lack of available clinical profile parameter reference ranges to discriminate healthy fish from those affected by specific disease conditions. Here, we describe our experience investigating poorly performing rainbow trout (Oncorhynchus mykiss) in an intensive recirculation aquaculture, where reaching a final diagnosis of nephrocalcinosis was not as straightforward as one would wish. To list the issues making the diagnosis difficult, it was necessary to consider the creeping onset of the problem. Further diagnostic steps needed to ensure success included obtaining comparative data for fish blood profiles and water quality from both test and control aquacultural systems, excluding infections with salmonid pathogenic agents and evaluating necropsy findings. Major events in the pathophysiology of nephrocalcinosis could be reconstructed as follows: aquatic environment hyperoxia and hypercapnia → blood hypercapnia → blood acid-base perturbation (respiratory acidosis) → metabolic compensation (blood bicarbonate elevation and kidney phosphate excretion) → a rise in blood pH → calcium phosphate precipitation and deposition in tissues. This case highlights the need to consider the interplay between water quality and fish health when diagnosing fish diseases and reaching causal diagnoses.

No abstract

No abstract

The pollution of surface waters by excessive biogenic elements, especially phosphorus, is a highly topical subject. Fishery management on ponds may be one of the potential sources of phosphorus in waters. Cyprinid fish generally have a very poor digestion of the phosphorus contained in the plant-based components of feeds. In them, phosphorus is deposited in the form of phytic acid which is almost indigestible for cyprinids. The conducted testing was focused on affecting the digestibility of phosphorus contained in plant-based feeds. Two of the cereals most frequently grown in the Czech Republic were tested, namely, wheat and barley. Control feeds were varieties commonly grown in our country, i.e. Vánek and Bojos. Furthermore, we used special cereal mutant lines with a decreased content of the phytic acid, JS-12/IDO 563 and M955. The test results showed that when using the low-phytate wheat line, the digestibility of phosphorus was increased by up to 11.21 % (P < 0.01); and by 5.89 % (P < 0.05) in the case of barley. Both low-phytate lines of the cereals used significantly affect phosphorus digestibility and decrease the loading of the environment with phosphorus. When using the low-phytate wheat line, a significant effect (P < 0.05) was found on the fat content in the fish body compared to the control variety but also compared to the low-phytate barley line. No significant effect was found comparing both control varieties and comparing the barley varieties mutually.

The aim of the study was to conduct a detailed research of aquatic invertebrates in the intensive breeding system of salmonid fish in order to determine the taxonomic composition of the community and its seasonal dynamics, and to identify those species that may be hosts of parasitic disease agents. To date, this issue has not been studied at all in the Czech Republic. Monitoring was conducted on the Danish type recirculation system near the municipality of Pravíkov in the Highlands of the Czech Republic from April till November 2015. A total of 9 series of samples were taken. Macrozoobenthos was evaluated in terms of taxonomic composition and abundance. Basic physicochemical properties of water (temperature, oxygen concentration, pH and conductivity) were also measured. In total, 69 taxa of aquatic invertebrates were noted, with the wall being the richest with a mean abundance of 756 pcs/m 2 . Permanent groups predominated; the most numerous group was the subphylum Crustaceae, represented by a single species, Asellus aquticus.

Intensive fish farming is associated with a high level of stress, causing immunosuppression. Immunomodulators of natural origin, such as probiotics or phytoadditives, represent a promising alternative for increasing the immune function of fish. In this study, we tested the autochthonous trout probiotic strain L. plantarum R2 in a newly developed, low-cost application form ensuring the rapid revitalization of bacteria. We tested continuous and cyclic feeding regimes with regard to their effect on the intestinal immune response and microbiota of rainbow trout. We found that during the continuous application of probiotic feed, the immune system adapts to the immunomodulator and there is no substantial stimulation of the intestinal immune response. During the cyclic treatment, after a 3-week break in probiotic feeding and the reintroduction of probiotics, there was a significant stimulation of the gene expression of molecules associated with both cellular and humoral immunity (CD8, TGF-β, IL8, TLR9), without affecting the gene expression for IL1 and TNF-α. We can conclude that, in aquaculture, this probiotic feed can be used with a continuous application, which does not cause excessive immunostimulation, or with a cyclic application, which provides the opportunity to stimulate the immunity of trout, for example, in periods of stress.