Gene expression patterns in Atlantic salmon (Salmo salar) with severe nephrocalcinosis

Diet-induced nephrocalcinosis in aquarium-raised juvenile spotted wolffish Anarhichas minor

Wolffish are regularly housed in aquaria, but little data on their husbandry and health is available for caretakers. High occurrence rates of nephrocalcinosis and urolithiasis have been observed in Atlantic Anarhichas lupus and spotted A. minor wolffish housed at 2 Canadian zoological institutions. To explore the effect of diet on nephrocalcinosis and urolithiasis development, a 16 mo prospective study was conducted. A total of 32 juvenile spotted wolffish were randomly assigned to one of 4 experimental groups fed exclusively with the following diet: (1) Skretting® Europa 18 pellets; (2) Mazuri® LS Aquatic Carni-Blend Diet Formula; (3) vitamin-supplemented fish-based diet, and (4) vitamin-supplemented invertebrate-based diet. Urinalysis, radiographs, and complete necropsies were performed at the end of the study. None of the wolffish developed uroliths during the study period. All specimens fed with the fish-based and invertebrate-based diets developed nephrocalcinosis, whereas this condition was seen in 12.5 and 0% of the fish in the Skretting® and Mazuri® groups, respectively. Affected wolffish often presented with oxalate crystalluria and increased radiodensity of the posterior kidneys. Urinalysis and radiographic study were considered useful in the antemortem diagnosis of nephrocalcinosis. None of the previously published risk factors for the development of nephrocalcinosis in fish were supported by the results of this study. However, nutritional analyses of the 4 diets suggest that high dietary levels of gelatin or vitamin C or low levels of vitamin E could be potential risk factors for the development of nephrocalcinosis in spotted wolffish and thus warrant further study.

Nephrocalcinosis in farmed salmonids: diagnostic challenges associated with low performance and sporadic mortality

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.