Implications of GI function for gas exchange, acid–base balance and nitrogen metabolism

Effects of Replacing Fishmeal with American Cockroach Residue on the Growth Performance, Metabolism, Intestinal Morphology, and Antioxidant Capacity of Juvenile Cyprinus carpio

Five isonitrogenous and isolipidic diets (Diet 1-Diet 5, with Diet 1 as the control) were formulated to replace 0%, 20%, 40%, 60%, and 80% of fishmeal with American cockroach residue. Juvenile Cyprinus carpio (initial body weight approximately 74 g) were randomly assigned to these diets for a 10-week feeding trial. The Diet 3 group (40% replacement) showed significantly higher final body weight, weight gain rate, specific growth rate, and protein efficiency ratio compared to other groups. No significant differences were observed in crude protein, ash, and total amino acid content across the diets. Groups fed Diet 1 and Diet 2 exhibited higher intestinal trypsin, lipase, α-amylase, and hepatic trypsin activities. Serum triglyceride (TG) levels were highest in the Diet 5 group. Hepatic aspartate aminotransferase (AST) activity was significantly lower in the Diet 3 and Diet 5 groups compared to Diet 1. Serum urea nitrogen levels followed a non-linear trend, initially increasing, then decreasing, and rising again with increasing fishmeal replacement. No significant differences were found in serum total protein (TP) levels among the dietary groups. Intestinal villus number, muscle layer thickness, villus height, villus width, and crypt depth remained consistent across groups. However, goblet cell numbers were significantly reduced at the 60% replacement level, which could impair intestinal barrier function. Diet 3 showed higher serum and hepatic total superoxide dismutase (T-SOD) activity, while Diet 2 had the highest hepatic total antioxidant capacity (T-AOC) activity. Hepatic malondialdehyde (MDA) levels were lowest in the Diet 2 and Diet 5 groups. Immunoglobulin M (IgM) levels showed an increasing trend with higher fishmeal replacement levels. In conclusion, replacing fishmeal with American cockroach residue did not adversely affect growth performance or body composition in juvenile C. carpio. Substituting 20-40% of fishmeal with American cockroach residue enhanced antioxidant capacity and immune function in juvenile C. carpio.

Multi-tissue metabolomic profiling reveals the crucial metabolites and pathways associated with scallop growth

BACKGROUND

Bivalves represent a vital economic resource in aquaculture for their high productivity and extensive market demand. Growth is one of the most important and desired aquaculture traits for bivalves, regulated by multiple levels, notably intricate metabolic processes. However, the understanding of the metabolic profiles that influence bivalve growth is limited, particularly from a multi-tissue perspective.

RESULTS

In this study, metabolic profiles of multiple tissues of Chlamys farreri with different growth performance were systematically investigated by ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Through comparing the metabolic variation between fast-growing (FG) scallops and slow-growing (SG) scallops, 613, 509, 105, and 192 significantly different metabolites (SDMs) were identified in the mantle, gill, adductor muscle, and digestive gland, respectively. Growth-related metabolic pathways including sphingolipid metabolism, fatty acid biosynthesis, and ABC transporter pathway, along with 11 SDMs associated with growth traits were identified in all four tissues, implying they were involved in the growth of multiple tissues in scallops. Tissue-specific metabolic profiling indicated that sulfur-containing amino acid metabolism in the mantle potentially contributed to shell growth, while the gill synergistically participated with the mantle through various metabolic processes, such as tyrosine metabolism, glycine, serine, and threonine metabolism and melanogenesis; energy metabolism was crucial for adductor muscle growth; and nutrients digestion and absorption in the digestive gland were linked to scallop growth.

CONCLUSIONS

Our results represent the first comprehensive analysis of the crucial pathways and metabolites associated with the growth of C. farreri, offering valuable insights for future bivalve aquaculture production.

An in vitro analysis of intestinal ammonia transport in fasted and fed freshwater rainbow trout: roles of NKCC, K+ channels, and Na+, K+ ATPase

We examined mechanisms of ammonia handling in the anterior, mid, and posterior intestine of unfed and fed freshwater rainbow trout (Oncorhynchus mykiss), with a focus on the Na⁺:K⁺:2Cl^- co-transporter (NKCC), Na⁺:K ⁺-ATPase (NKA), and K⁺ channels. NKCC was localized by immunohistochemistry to the mucosal (apical) surface of enterocytes, and NKCC mRNA was upregulated after feeding in the anterior and posterior segments. NH₄⁺ was equally potent to K⁺ in supporting NKA activity in all intestinal sections. In vitro gut sac preparations were employed to examine mucosal ammonia flux rates (Jm_amm, disappearance from the mucosal saline), serosal ammonia flux rates (Js_amm, appearance in the serosal saline), and total tissue ammonia production rates (Jt_amm = Js_amm - Jm_amm). Bumetanide (10^-4 mol L^-1), a blocker of NKCC, inhibited Js_amm in most preparations, but this was largely due to reduction of Jt_amm; Jm_amm was significantly inhibited only in the anterior intestine of fed animals. Ouabain (10^-4 mol L^-1), a blocker of NKA, generally reduced both Jm_amm and Js_amm without effects on Jt_amm in most preparations, though the anterior intestine was resistant after feeding. Barium (10^-2 mol L^-1), a blocker of K⁺ channels, inhibited Jm_amm in most preparations, and Js_amm in some, without effects on Jt_amm. These pharmacological results, together with responses to manipulations of serosal and mucosal Na⁺ and K⁺ concentrations, suggest that NKCC is not as important in ammonia absorption as previously believed. NH₄⁺ appears to be taken up through barium-sensitive K⁺ channels on the mucosal surface. Mucosal NH₄⁺ uptake via both NKCC and K⁺ channels is energized by basolateral NKA, which plays an additional role in scavenging NH₄⁺ on the serosal surface to possibly minimize blood toxicity or enhance ion uptake and amino acid synthesis following feeding. Together with recent findings from other studies, we have provided an updated model to describe the current understanding of intestinal ammonia transport in teleost fish.

Oil toxicity and implications for environmental tolerance in fish

Crude oil and its constituent chemicals are common environmental toxicants in aquatic environments worldwide, and have been the subject of intense research for decades. Importantly, aquatic environments are also the sites of numerous other environmental disturbances that can impact the endemic fauna. While there have been a number of attempts to explore the potential additive and synergistic effects of oil exposure and environmental stressors, many of these efforts have focused on the cumulative effects on typical toxicological endpoints (e.g. survival, growth, reproduction and cellular damage). Fewer studies have investigated the impact that oil exposure may have on the ability of exposed animals to tolerate typically encountered environmental stressors, despite the fact that this is an important consideration when placing oil spills in an ecological context. Here we review the available data and highlight potentially understudied areas relating to how oil exposure may impair organismal responses to common environmental stressors in fishes. We focused on four common environmental stressors in aquatic environments - hypoxia, temperature, salinity and acid-base disturbances - while also considering social stress and impacts on the hypothalamus-pituitary-interrenal axis. Overall, we believe the evidence supports treating the impacts of oil exposure on environmental tolerance as an independent endpoint of toxicity in fishes.

Osmoregulatory bicarbonate secretion exploits H(+)-sensitive haemoglobins to autoregulate intestinal O2 delivery in euryhaline teleosts

Marine teleost fish secrete bicarbonate (HCO3 (-)) into the intestine to aid osmoregulation and limit Ca(2+) uptake by carbonate precipitation. Intestinal HCO3 (-) secretion is associated with an equimolar transport of protons (H(+)) into the blood, both being proportional to environmental salinity. We hypothesized that the H(+)-sensitive haemoglobin (Hb) system of seawater teleosts could be exploited via the Bohr and/or Root effects (reduced Hb-O2 affinity and/or capacity with decreasing pH) to improve O2 delivery to intestinal cells during high metabolic demand associated with osmoregulation. To test this, we characterized H(+) equilibria and gas exchange properties of European flounder (Platichthys flesus) haemoglobin and constructed a model incorporating these values, intestinal blood flow rates and arterial-venous acidification at three different environmental salinities (33, 60 and 90). The model suggested red blood cell pH (pHi) during passage through intestinal capillaries could be reduced by 0.14-0.33 units (depending on external salinity) which is sufficient to activate the Bohr effect (Bohr coefficient of -0.63), and perhaps even the Root effect, and enhance tissue O2 delivery by up to 42 % without changing blood flow. In vivo measurements of intestinal venous blood pH were not possible in flounder but were in seawater-acclimated rainbow trout which confirmed a blood acidification of no less than 0.2 units (equivalent to -0.12 for pHi). When using trout-specific values for the model variables, predicted values were consistent with measured in vivo values, further supporting the model. Thus this system is an elegant example of autoregulation: as the need for costly osmoregulatory processes (including HCO3 (-) secretion) increases at higher environmental salinity, so does the enhancement of O2 delivery to the intestine via a localized acidosis and the Bohr (and possibly Root) effect.