Physiology and aquaculture: A review of ion and acid‐base regulation by the gills of fishes

Abstract

Fish aquaculture facilities strive to maintain abiotic conditions that optimise somatic growth. Two physiological systems that are critically linked to environmental abiotic factors are ion and acid-base regulation. Given the detrimental effects of ionic and acid-base imbalances coupled with the potential energetic costs of ion and acid-base regulation, it is important to understand how changes in abiotic variables such as salinity, temperature and pH alter ionoregulatory and acid-base physiology. The gill is the predominant site of ion and acid-base regulation, two linked processes that are vital to the health of fishes. Most species maintain ion levels in the blood plasma within a narrow range, independent of external ion concentrations. In freshwater (FW), fishes must actively take up ions from their dilute environment to counteract passive ion losses, while in seawater (SW), ion excretion serves to counteract passive salt gain. Ion uptake (FW) and excretion (SW) are coordinated by different subtypes of ion-transporting cells (ionocytes) expressed in the gill epithelium. In this review, we discuss the function of FW and SW ionocytes in the movement of ions across the gill epithelium and address other features of the gill that are integral to ionoregulation.We also discuss the mechanisms of acid-base regulation by the gill, which is intimately related to ion regulation because it is coordinated by Na + -and Cl − -linked fluxes of acid (H + ) and base (HCO − 3 ) equivalents. These fundamental physiological principles are integral in understanding how fishes in aquaculture respond to relevant disturbances that may occur under culture conditions.

Gill histology and ultrastructure in Aplysia depilans (Mollusca, Euopisthobranchia)

“…Therefore, these gills seem to have a role in ion exchanges in addition to respiratory function (Jonas, 1986; Rodriguez et al, 2019). Ion regulation is known to occur in the gills of cephalopods, crustaceans, and fish (Lin et al, 2022; McNamara & Faria, 2012; Zimmer & Perry, 2022), and was considered an ancestral function of gills (Sackville et al, 2022).…”

Insights into the control and consequences of breathing adjustments in fishes-from larvae to adults

“…The associated reduction in gas transfer efficiency is of no consequence to blood O 2 transport because the arterial PO 2 will remain well in excess of that needed for full saturation of haemoglobin. However, the retention of CO 2 associated with hypoventilation elicits respiratory acidosis (a lowering of pH caused by an increase in PCO 2 ) ( Wood and Jackson, 1980 ), an obvious detrimental consequence of hyperoxia exposure that could impact fish health in commercial aquaculture settings that add supplemental O 2 to the water ( Zimmer and Perry, 2022 ).…”

Mechanisms of Na+ uptake from freshwater habitats in animals

“…Several excellent reviews on osmoregulation are available for teleost fish ( Evans et al, 2005 ; Hwang and Lee, 2007 ; Hwang et al, 2011 ; Hiroi and McCormick, 2012 ; Takei et al, 2014 ; Zimmer and Perry, 2022 ), including those with a focus on freshwater environments ( Kirschner, 2004 ; Evans 2011 ; Hwang, 2011 ; Dymowska et al, 2012 ; Zimmer et al, 2017 ). However, only a few species have been thoroughly investigated, among them zebrafish Danio rerio , Mozambique tilapia Oreochromis mossambicus , killifish Fundulus heteroclitus , medaka Oryzias latipes ( Hsu et al, 2014 ), and rainbow trout Oncorhynchus mykiss ( Dymowska et al, 2012 ).…”

“…In teleost fish, ion uptake mechanisms are very diverse, possibly due to major evolutionary changes in genome architecture and diversification of ion transporter gene families ( Desvignes et al, 2021 ). Numerous studies have described these diverse ion uptake mechanisms in fish, but only in a few species ( Dymowska et al, 2012 ; Hwang and Chou, 2013 ; Zimmer and Perry, 2022 ).…”