Physio-biochemical, metabolic nitrogen excretion and ion-regulatory assessment in largemouth bass (Micropterus salmoides) following exposure to high environmental iron

Elevated concentrations of organic and inorganic forms of iron in plant-based diets for channel catfish prevent anemia but damage liver and intestine, respectively, without impacting growth performance

We compared the effects of using inorganic and organic forms of iron in plant-based diets on catfish performance in a feeding trial with 6-g catfish fingerlings. The objective was to determine whether dietary iron in excess of known requirements negatively affected the fish. Five diets supplemented with 0 (basal), 125, 250 mg Fe/kg of either FeSO₄ or iron methionine were formulated. Weight gain, feed conversion ratio, hepatosomatic index, and survival were similar among diets. Plasma and intestine iron concentration was similar among diets. Whole-body total lipid, protein, and dry matter were similar among diets, while ash content was higher in fish fed the basal diet. Total liver iron concentration was higher in fish fed diets supplemented with 250 mg Fe/kg in both iron forms than other diets. Hematological parameters were similar among treatments. Liver necrosis, inflammation, and vacuolization were highest in fish fed the diet supplemented with 250 mg Fe/kg from organic iron, followed by those fed diets with 250 mg Fe/kg from inorganic iron. Inorganic iron-supplemented diets caused more intestinal inflammation (increased inflammatory cells, villi swelling, thicker lamina propria) than the organic iron-supplemented diets or basal diet. Organic iron at 250 mg/kg resulted in a $0.143/kg increase in feed cost. Latent iron deficiency and initial signs of anemia developed in catfish fed the basal diet. Supplemental iron from either form prevented iron deficiency. Organic iron at 125 mg/kg optimized fish performance at a cost comparable to that of fish fed other diets, but without overt negative effects.

Regulation of Rhesus glycoprotein-related genes in large-scale loach Paramisgurnus dabryanus during ammonia loading

Waterborne ammonia is one of the crucial issues that limited production and animal health in aquaculture. Ammonia-tolerant varieties are highly desired in intensive fish farming. Screening for the key regulatory genes of ammonia tolerance is essential for variety breeding. According to the previous hypothesis, Rh glycoproteins play an important role in ammonia excretion in teleosts. However, the ammonia defensive mechanisms are not well described at present for large-scale loach (Paramisgurnus dabryanus), a typical air-breathing and commercially important fish in East Asia. Here we show that the transcription of Rh glycoprotein-related genes was significantly affected by ammonia exposure in this species. Probit analysis showed that 96 h-LC₅₀ of NH₄Cl at 23 ℃ and pH 7.2 was 92.64 mmol/L. A significant increase of Rhcg expression in gills was observed after 48 h of 60 mmol/L and 36 h of 80 mmol/L NH₄Cl exposure, suggesting that Rhcg present on the apical side of the branchial epithelium facilitates NH₃ excretion out of gills. A high concentration of acute ammonia exposure induced elevated Rhbg transcript in the gills of large-scale loaches, while a slight change in Rhbg expression was observed in response to lower ammonia, suggesting that transcriptions of Rhbg genes are activated by a considerably high level of ambient ammonia to eliminate excessive endogenous nitrogen. The Rhag mRNA level in gills of large-scale loaches increased markedly with the prolonging of exposure time from 0 to 36 h of ammonia loading, suggesting Rhag localized in gills may be primarily associated with ammonia handling. During 7-21 days of ammonia exposure, the expression of most Rh glycoproteins-related genes in the gills decreased, indicating that the functional role of Rh glycoproteins is not primarily associated with ammonia defense over a long period (more than 7 days). Although a significant transcript of Rhbg was found in the skin of a large-scale loach, the lack of Rhcg and down-regulation of Rhag may indicate that the skin is not an essential location of ammonia excretion, at least when submerged to high levels of ammonia in the environment. In conclusion, Rh glycoproteins localized in gills as ammonia transporters play a momentous role in ammonia detoxification in this species during acute ammonia loading. However, it does not show a positive function during long-term ammonia exposure. Furthermore, the physiological function of Rh glycoproteins localized in the skin is still unclear and deserves further study.

Co-exposure of iron oxide nanoparticles and glyphosate-based herbicide promote liver toxicity in guppy (Poecilia reticulata): A histochemical and ultrastructural approach

Citrate functionalized iron oxide nanoparticles (IONPs) are employed for various purposes-including environmental remediation but the interaction of IONPs with aquatic contaminants is poorly understood. Among those, glyphosate-based herbicides are toxic and affect target organs such as the liver. Evaluations of livers of female Poecilia reticulata by exposures to IONPs at a concentration of 0.3 mg/L were performed with association to: (1) 0.65 mg of glyphosate per litter and (2) 1.3 mg of glyphosate per litter of Roundup Original, and (3) glyphosate P.A at 0.65 mg/L. These associations were carried out progressively, after 7, 14, and 21 days. We detected circulatory disturbances, inflammatory responses, activation of the immune system, regressive changes, and progressive responses with changes in the connective tissue and decreased glycogen reserve from days 14 to 21. Ultrastructural changes in the Disse space and microvilli of hepatocytes indicated decreased contact surface area. In general, the damage was time and concentration dependent, increasing from 7 to 14 days and tending to stabilize from 14 to 21 days. Therefore, herbicide-associated IONPs functioned as xenobiotics inducing intense cellular detoxification processes and activation of hepatic immune responses.

Coping strategies in response to different levels of elevated water hardness in channel catfish (Ictalurus punctatus): Insight into ion-regulatory and histopathological modulations

Water hardness above the optimal level can incite toxic effects in fish, which are often species specific. Hence, we aimed at obtaining insights on the potential effects of elevated water hardness as well as coping strategies in channel catfish (Ictalurus punctatus). First, a toxicity assay was performed where the 96 h-LC₅₀ was calculated as 4939 mg/L CaCO₃. Thereafter, to gain knowledge on the underlying adaptive strategies to high water hardness, fish were exposed to seven hardness levels (150, 600, 1000, 1500, 2000, 3000 and 4000 mg/L CaCO₃ at pH 8.15) for 15 days. Results showed that branchial activities of Ca²⁺-ATPase and Na⁺/K^+-ATPase, which facilitate Ca²⁺ uptake, reduced starting respectively from 1000 mg/L and 1500 mg/L CaCO₃. Nevertheless, Ca²⁺ burden in plasma and tissue (gills, liver and intestine) remained elevated. Hardness exposure also disturbed cations (Na⁺, K⁺, Mg²⁺) and minerals (iron and phosphorus) homeostasis in a tissue-specific and dose-dependent manner. Both hemoglobin content and hematocrit dropped significantly at 3000-4000 mg/L CaCO₃, with a parallel decline in iron content in plasma and gills. Muscle water content rose dramatically at 4000 mg/L CaCO₃, indicating an osmo-regulation disruption. Higher hardness of 3000-4000 mg/L CaCO₃ also incited a series of histopathological modifications in gills, liver and intestine; most likely due to excess Ca²⁺ accumulation. Overall, these data suggest that channel catfish can adapt to a wide range of elevated hardness by modulating Ca²⁺ regulatory pathways and histomorphological alterations, however, 1500 mg/L CaCO₃ and above can impair the performance of this species.