Acute waterborne cadmium uptake in rainbow trout is reduced by dietary calcium carbonate

Cadmium induced bioaccumulation, histopathology, gene regulation in fish and its amelioration - A review

Different anthropogenic activities as well as natural sources contribute enormously towards various heavy metal contaminations in aquatic habitats. Cadmium (Cd) is one of most prevalent and toxic heavy metals with a long half life. Unlike terrestrial animals, exposure of Cd in fishes may happen not only through feeds but also from its habitat water. Bioaccumulation of Cd in fishes occurs in many tissues, but mainly in gill, liver, kidney, skin, and muscle. The concentrations of Cd in fish tissues depend upon the extent and duration of Cd exposure, species and age of fishes, dietary minerals and antioxidant concentrations, and habitat water quality. Specific histopathological observations in liver, kidney, and gill are useful to understand the effects of Cd, which could help to determine the ameliorating methods to be adopted. Exposure of Cd exerts several adverse effects on general growth and development, reproductive processes, osmoregulation, morphological and histological structures, stress tolerance, and endocrine system, mainly due to changes in biological functions induced by differential expressions of several genes related to oxidative stress, apoptosis, inflammation, immunosuppressions, genotoxicity, Cd chelation and carbohydrate metabolism. Chronic biomagnifications of Cd exceeding the permitted level may be harmful not only to the fishes itself but also to humans through food chains. Amelioration of such toxic heavy metal that has been categorized as a potent carcinogenic in humans is of utmost importance. Main modes of amelioration encompas reducing oxidative damages by promoting the antioxidative defenses, decreasing Cd absorption, increasing excretion through excretory system and improving the tolerance of fishes to Cd toxicity. Many amelioration measures such as use of minerals (for example, zinc, calcium, and iron), vitamins (vitamin C, A, and E), different herbs, probiotics and other agents (taurine, bentonite, chitosan, zeolite, and metallothionein) have been explored for their effective roles to reduce Cd bioaccumulation and toxicity symptoms in fishes. The present review discusses bioaccumulation of Cd, histopathological alterations, oxidative stress, synergism-antagonism, and gene regulation in different tissues, and its amelioration measures in fishes.

Protective effects of calcium against cadmium-induced toxicity in juvenile grass carp (Ctenopharyngodon idellus)

Cadmium (Cd) is one of the dominant metal pollutants present in the aquatic environment that affects ion homeostasis, oxidative stress (OS) and immune responses of aquatic organisms. Given the physicochemical similarities between Cd²⁺ and calcium (Ca²⁺) ions, their antagonism may facilitate the mitigation of Cd-induced toxicity. To better understand the role of Ca in protecting against Cd-induced toxicity in teleosts, juvenile grass carp were exposed to Cd (measured concentration 3 μg/L) and a gradient of Ca concentrations (measured concentration 1.5 mg/L, 2.5 mg/L, 3.0 mg/L, and 3.5 mg/L in the control (CTL) group, low calcium (LCA) group, medium calcium (MCA) group, and high calcium (HCA) group, respectively) for 30 days. Inductively coupled plasma mass spectrometry (ICP-MS) data analyses showed that simultaneous exposure to Ca impaired the accumulation of Cd in all tested tissues. Besides, Ca addition maintained the plasma ion (Na⁺, K⁺, Cl^-) homeostasis, alleviated Cd-induced oxidative stress (OS), and regulated the activities and transcriptional levels of ATPase. Furthermore, transcriptional heatmap analysis demonstrated that several indicator genes for OS and calcium signaling pathway were found to be significantly modulated by Ca addition. This work delineates a protective effect of Ca against Cd-induced toxicity in grass carp, providing new insight into the possible solutions to Cd pollution issues in aquaculture industry.

Can human nutrition be improved through better fish feeding practices? a review paper

Achieving Sustainable Development Goal 2 of zero hunger and malnutrition by 2030 will require dietary shifts that include increasing the consumption of nutrient dense foods by populations in low- and middle-income countries. Animal source foods are known to be rich in a number of highly bioavailable nutrients that otherwise are not often consumed in the staple-food based diets of poorer populations throughout the world. Fish is the dominant animal source food in many low- and middle-income countries in the global south and is available from both fisheries and aquaculture. Consumers often perceive that wild caught fish have higher nutritional value than fish produced through aquaculture, and this may be true for some nutrients, for example omega-3 fatty acid content. However, there is potential to modify the nutritional value of farmed fish through feeds and through production systems, illustrated by the common practice of supplementing omega-3 fatty acids in fish diets to optimize their fatty acid profile. This manuscript reviews the evidence related to fish feeds and the nutritional composition of fish with respect to a number of nutrients of interest to human health, including iron, zinc, vitamins A and D, selenium, calcium, and omega-3 fatty acids, with low- and middle-income country populations in mind. In general, we find that the research on fortification of fish diet particularly with vitamins and minerals has not been directed toward human health but rather toward improvement of fish growth and health performance. We were unable to identify any studies directly exploring the impact of fish feed modification on the health of human consumers of fish, but as nutrition and health rises in the development agenda and consumer attention, the topic requires more urgent attention in future feed formulations.

Non-invasive in vivo imaging of the ionic regimes along the gastrointestinal tract of a freshwater vertebrate model organism (Japanese medaka) using responsive photonic crystal beads

Microspherical photonic colloidal crystalline beads that are responsive to media ionic strength of cationic electrolytes have been developed for in vivo imaging of the morphology and concentration gradient of cationic electrolytes along the gastrointestinal (GI) tract of live Japanese medaka (Oryzias latipes). These responsive photonic beads were assembled from core-shell nano-sized particles with polystyrene-co-polyacrylic acid (PS-co-PAA) cores and poly(hydroxyethyl methacrylate-co-p-styrene sulfonate) (PHEMA-co-PSS) hydrogel shells. The three-dimensional orderly packing of these nano-sized core-shell particles gave rise to the photonic properties of the resultant colloidal crystalline array of microspheres. The cationic electrolyte-induced volume phase transition of the sulfonate-laden hydrogel shells of the nano-sized particles altered the lattice spacing among those particles and brought about the photonic responses of the colloidal crystalline beads. Unambiguous changes in the diffraction colour of the colloidal crystalline beads were observable under ordinary ambient light in solution media of increasing concentration of sodium chloride up to 500 mM. These photonic colloidal crystalline beads were found to possess enough structural integrity for in vivo imaging of the GI tract of live Japanese medaka. With the use of a conventional optical microscope, the gradient in the ionic strength of cationic electrolytes along the GI tract of live Japanese medaka larvae was readily revealed, with a lower electrolyte concentration in the mid-intestine (<50 mM) compared to that of the posterior-intestine (≥50 mM). Our results demonstrated the potential of stimuli-responsive photonic materials in bio-imaging applications.