Role of the kidneys in acid-base regulation and ammonia excretion in freshwater and seawater fish: implications for nephrocalcinosis

Gulf toadfish (Opsanus beta) urinary bladder ion and water transport is enhanced by acclimation to higher salinity to serve water balance

Marine teleosts experience ion gain and water loss in their natural habitats. Among other tissues, the urinary bladder epithelium of marine fishes has been shown to actively transport ions to facilitate water absorption. However, transport properties of the urinary bladder epithelium of marine fishes and its plasticity in altered ambient salinities is relatively under-investigated. We describe urinary bladder epithelium electrophysiology, water flux, and expressions of ion transporters in urinary bladder tissue of Gulf toadfish (Opsanus beta) acclimated to either 35 ppt or 60 ppt seawater. Water absorption in bladder sac preparations increased ∼350% upon acclimation to 60 ppt. Increases in water transport coincided with a significant ∼137% increase in urinary bladder tissue mucosal-to-serosal short circuit current (Isc) and a ∼56% decrease in tissue membrane resistance. Collectively, these metrics indicate that an active electrogenic system facilitates water absorption via Na+ (and Cl-) transport in urinary bladder tissue. Furthermore, pharmacological inhibition of urinary bladder tissue Isc and expression of a suite of ion transporters and channels previously unidentified in this tissue provide mechanistic insights into the transport processes responsible for water flux. Analysis of water transport to overall Gulf toadfish water balance reveals a modest water conservation role for the urinary bladder of ∼0.5% of total water absorption in 35 ppt and 1.9% in 60 ppt acclimated toadfish. These results emphasize that electrogenic ion transport facilitates water-absorptive properties of the urinary bladder in Gulf toadfish-a process that is regulated to facilitate water homeostasis.NEW & NOTEWORTHY Novel experiments showcasing increased urinary bladder water absorption, ion transport, and altered channel/transporter expression in a marine fish acclimated to high salinities. Our results provide additional and noteworthy mechanistic insight into the ionoregulatory processes controlling water transport at the level of the urinary bladder in marine teleosts. Experimental outcomes are applied to whole organism-level water transport values, and the relative importance of marine teleost urinary bladder function to overall organism water conservatory measures is discussed.

Performance and land characteristics of brackishwater pond to support sustainability of Pacific white shrimp (Litopenaeus vannamei) culture intensive technology

Intensive technology Pacific white shrimp (Litopenaeus vannamei) culture has been applied in Bulukumba Regency, South Sulawesi Province, but information on the performance of Pacific white shrimp culture and the land characteristics or environment of the pond has not yet been obtained. The research purposes are to find out the performance and the land characteristics or environment of Pacific white shrimp culture intensive technology to serve as a basis for determining the culture development. Five transects perpendicular to the shoreline and three transects parallel to the coastline, or 15 water sample stations, were identified in the field. Other data was obtained from the extraction of Sentinel-2 and SPOT (Satellite pour l'Observation de la Terre) satellite imagery 7. The size of intensive technology Pacific white shrimp culture ponds in Bulukumba Regency ranges from 1600 to 5000 m2 which is stocked with fry with a stocking density of 100-300 ind./m2 which can produce 12.0-50.0 tons/ha/cycle after rearing for 100-142 days of culture with a food conversion ratio of 1.2:1-2.0:1. The land characteristics of intensive technology Pacific white shrimp culture ponds in Bulukumba Regency are characterized by elevation from 10.0 to 20.0 m above sea level, wavy topography, tidal range between 1.35 and 1.70 m, dominated by Latosol or Cambisol and Alfisol or Mediterranean soil great groups, the quality of the source water can generally support Pacific white shrimp culture, and the annual rainfall is from 1341 to 1763 mm and it is not built on former mangrove land. It is recommended that existing Pacific white shrimp culture ponds increase the capacity and capability of their wastewater treatment plant ponds and implement better water management and feed management so that the quality of wastewater from intensive technology Pacific white shrimp culture ponds can also be better so that productivity can be increased and sustainable.

Differential regulation of magnesium transporters Slc41, Cnnm and Trpm6-7 in the kidney of salmonids may represent evolutionary adaptations to high salinity environments

Magnesium is important for enzymatic reactions and physiological functions, and its intracellular concentration is tightly regulated. Atlantic salmon has the ability to handle large changes in environmental Mg2+ concentration when migrating between freshwater and seawater habitats, making it a relevant model to investigate Mg2+ homeostasis. Parr-smolt transformation (PST) is a life history transition which prepares the freshwater juvenile for the marine environment. The kidney is one of the key organs involved in handling higher salt load in teleosts. Though several key Mg2+ transport families (SLC41, CNNM and TRPM6-7) have recently been identified in mammals and a few fishes, the molecular bases of Mg2+ homeostasis in salmon are not known. We found that all three families are represented in the salmon genome and exhibit a clear conservation of key functional domains and residues. Present study indicates a selective retention of paralogous Mg2+ transporters from the fourth whole genome duplication round (Ss4R) and a differential regulation of these genes, which suggests neo- and/or sub-functionalization events. slc41a1-1, cnnm4a1, -4a2 and trpm7-2 are the main upregulated genes in the kidney during PST and remain high or further increase after exposure to seawater (33 ppt). By contrast, slc41a1-2, -3a, cnnm3-1, and cnnm3-2 are only upregulated after seawater exposure. In addition, slc41a1-1, -2, and trpm7-2 respond when exposed to brackish water (12 ppt), while cnnm3-1 and cnnm3-2 do not, indicating the existence of a lower salinity threshold response for these members. Finally, the response of slc41a1-1, -2 and trpm7-2 in salmon was significantly reduced or completely abolished when exposed to Mg2+-reduced brackish water, while others were not, suggesting they might be specifically regulated by Mg2+. Our results are consistent with previous findings on other euryhaline teleosts and chondrichthyan species, suggesting the existence of common adaptive strategies to thrive in high salinity environments. Concomitantly, salmonid-specific innovations, such as differential regulation and recruitment of family members not previously shown to be regulated in the kidney (Cnnm1 and Cnnm4) of other vertebrates might point to adaptions associated with their very plastic anadromous life cycle.

Metazoan parasite community of Leporinus piau Fowler, 1941 (Anostomidae, Characiformes), an endemic freshwater fish from the Caatinga domain, Brazil

The present study aimed to inventory the parasitic fauna of Leporinus piau from the Lima Campos weir, Salgado River basin, municipality of Icó, Ceará, Brazil. A total of 35 host specimens were collected, whereas all were parasitized by at least two metazoan taxa. A total of 2,910 parasite specimens belonging to five taxonomic groups were identified such as: Myxozoa (Henneguya sp. 1 and Henneguya sp. 2), Monogenea (Jainus beccus, Jainus radixelongatus, Tereancistrum flabellum, Tereancistrum paranaensis, Tereancistrum parvus, Urocleidoides digitabulum, Urocleidoides paradoxus, Urocleidoides sp., Dactylogyridae gen. sp. 1, Dactylogyridae gen. sp. 2 and Dactylogyridae gen. sp. 3), Digenea (Diplostomum lunaschiae and Clinostomum sp.), Nematoda (Procamallanus (Spirocamallanus) inopinatus) and Copepoda (Gamispatulus schizodontis). Seventeen parasite taxa were found, with the class Monogenea being the most abundant group. The main site of infestation was the gills, presenting 14 taxa, including myxozoans, monogeneans and digeneans. This study highlights seven new parasitic associations for the host and 16 for the studied locality, as well as new records of diversity indices for the parasitic taxa found. It was observed that the class Monogenea exhibited a broad diversity of species, contributing to the understanding of the distribution patterns of fish parasites in the Brazilian semiarid region.

The differential impact of iron on ferroptosis, oxidative stress, and inflammatory reaction in head-kidney macrophages of yellow catfish (Pelteobagrus fulvidraco) with and without ammonia stress

Ammonia toxicity in fish is closely related to ferroptosis, oxidative stress, and inflammatory responses. Iron is an essential trace element that plays a key role in many biological processes for cells and organisms, including ferroptosis, oxidative stress response, and inflammation. This study aimed to investigate the effect of iron on indicators of fish exposed to ammonia, specifically on the three aspects mentioned above. The head kidney macrophages of yellow catfish were randomly assigned to one of four groups: CON (normal control), AM (0.046 mg L-1 total ammonia nitrogen), Fe (20 μg mL-1 FeSO4), and Fe + AM (20 μg mL-1 FeSO4, 0.046 mg L-1 total ammonia nitrogen). The cells were pretreated with FeSO4 for 6 h followed by ammonia for 24 h. The study found that iron supplementation led to an excessive accumulation of iron and ROS in macrophages, but it did not strongly induce ferroptosis, oxidative stress, or inflammatory responses. This was supported by a decrease in T-AOC, and the downregulation of SOD, as well as an increase in GSH levels and the upregulation of TFR1, CAT and Nrf2. Furthermore, the mRNA expression of HIF-1, p53 and the anti-inflammatory M2 macrophage marker Arg-1 were upregulated. The results also showed that iron supplementation increased the progression of some macrophages from early apoptosis to late apoptotic cells. However, the combined treatment of iron and ammonia resulted in a stronger intracellular ferroptosis, oxidative stress, and inflammatory reaction compared to either treatment alone. Additionally, there was a noticeable increase in necrotic cells in the Fe + AM and AM groups. These findings indicate that the biological functions of iron in macrophages of fish may vary inconsistently in the presence or absence of ammonia stress.

Mechanisms and physiological relevance of acid-base exchange in functional units of the kidney

This review discusses the importance of homeostasis with a particular emphasis on the acid-base (AB) balance, a crucial aspect of pH regulation in living systems. Two primary organ systems correct deviations from the standard pH balance: the respiratory system via gas exchange and the kidneys via proton/bicarbonate secretion and reabsorption. Focusing on kidney functions, we describe the complexity of renal architecture and its challenges for experimental research. We address specific roles of different nephron segments (the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule) in pH homeostasis, while explaining the physiological significance of ion exchange processes maintained by the kidneys, particularly the role of bicarbonate ions (HCO3-) as an essential buffer system of the body. The review will be of interest to researchers in the fields of physiology, biochemistry and molecular biology, which builds a strong foundation and critically evaluates existing studies. Our review helps identify the gaps of knowledge by thoroughly understanding the existing literature related to kidney acid-base homeostasis.

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.