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This is the first study in an aquatic ectotherm to combine a stoichiometric bioenergetic approach with an endpoint stochastic model to explore dietary macronutrient content. The combination of measuring respiratory gas (O2 and CO2) exchange, nitrogenous (ammonia and urea) excretion, specific dynamic action (SDA), metabolic energy substrate use, and whole-body protein synthesis in spiny lobster, Sagmariasus verreauxi, was examined in relation to dietary protein. Three isoenergetic feeds were formulated with varying crude protein: 40%, 50% and 60%, corresponding to CP40, CP50 and CP60 treatments, respectively. Total CO2 and ammonia excretion, SDA magnitude and coefficient, and protein synthesis in the CP60 treatment were higher compared to the CP40 treatment. These differences demonstrate dietary protein influences post-prandial energy metabolism. Metabolic use of each major energy substrate varied at different post-prandial times, indicating suitable amounts of high-quality protein with major non-protein energy-yielding nutrients, lipid and carbohydrate, are critical for lobsters. The average contribution of protein oxidation was lowest in the CP50 treatment, suggesting mechanisms underlying the most efficient retention of dietary protein and suitable dietary inclusion. This study advances understanding of how deficient and surplus dietary protein affects energy metabolism and provides approaches for fine-scale feed evaluation to support sustainable aquaculture.

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The respiratory quotient (RQ) has been used extensively as an index to evaluate metabolic energy expenditure in terrestrial animals including humans. In contrast, RQ use in understanding physiology and nutrition of aquatic ectotherms has been restricted due to technical challenges in measuring total CO 2 in water. With technical advances in measuring total CO 2 in water, RQ in aquatic ectotherms can be accurately determined and is potentially available as a valuable method. Here, we provide a comprehensive review of studies on RQ and metabolic energy substrate use in aquatic ectotherms. Metabolic energy substrate use is evaluated by a reliable stoichiometric bioenergetic approach, based on measuring RQ and nitrogen quotient (NQ) simultaneously. Stoichiometry provides a nondestructive and unequivocal way to quantify the instantaneous oxidation of each major energy substrate (protein, lipid or carbohydrate). This review aims to refine knowledge about bioenergetics of aquatic ectotherms under different conditions including nutritional aspects of sustainable aquaculture. Notably, stoichiometry provides a promising approach to optimize feeds and feeding regimes to realize sustainable aquaculture under differing conditions and with differing feed ingredients. It also provides an approach to consider climate change impacts and physiological adaptation mechanisms for survival and development in farmed environments and natural ecosystems. Stoichiometric bioenergetics knowledge in aquatic ectotherms has relevance to commercial impacts in the face of overfishing and food security, and ecological significance in the face of environmental change scenarios. We suggest expanding the use of stoichiometry in future bioenergetic research in emerging aquaculture species.

Nonylphenol (NP) is a contaminant that has negative impacts on aquatic organisms. To investigate its phytotoxicity, bioaccumulation, and degradation in algae without associated bacteria, six freshwater microalgae—Ankistrodesmus acicularis, Chlorella vulgaris, Chroococcus minutus, Scenedesmus obliquus, Scenedesmus quadricauda, and Selenastrum bibraianum—in bacteria-free cultures were studied. When exposed to 0.5–3.0 mg L−1 NP for 4 days, cell growth and photosynthesis, including maximal photochemistry (Fv/Fm), were suppressed progressively. The antioxidant responses of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) showed species differences. While the antioxidant enzymes in C. vulgaris and S. obliquus were more active with the increase of NP (0–3 mg L−1), they dropped in the other four algae at concentrations of 1 and 1.5 mg L−1. Therefore, C. vulgaris and S. obliquus were designated as NP-tolerant species and showed more conspicuous and faster changes of antioxidant reactions compared with the four NP-sensitive species. All six species degraded NP, but A. acicularis was more reactive at low NP concentrations (<1 mg L−1), suggesting its possible application in sewage treatment for its potential for effective NP removal from water bodies in a suitable scope. Therefore, the conclusion is that biodegradation of NP by algae is species specific.

The effect of seawater pH on blood physiology in juvenile turbot Scophthalmus maximus (Linnaeus, 1758) reared in recirculating aquaculture systems (RAS) was examined. S. maximus (19.89±0.25 g) were exposed to six pH levels at 6.3±0.2, 6.8±0.2, 7.3±0.2, 7.8±0.2, 8.3±0.2 and 8.8±0.2. Haemoglobin content (HBC) at acidic conditions was higher compared to that under alkaline conditions. The frequency of total nuclear anomalies (FTNA) was high at pH levels below 7.3 or above 8.3. The relationship between FTNA and pH was well described using a quadratic equation. Alkaline phosphatase activity was significantly declined at pH above 8.3, while total superoxide dismutase activity (T-SOD) remained virtually unchanged among all treatments. This study demonstrated that HBC and FTNA can be used as reliable biomarkers to evaluate the effect of pH in aquatic ectotherms from physiological standpoints. Our findings suggest that environmental pH in RAS ranging from 6.8 to 7.8 is appropriate for juvenile turbot aquaculture.

Transforming growth factor-beta 1 (TGF-β1) as a member of TGF-β superfamily plays crucial roles in regulation of immune responses. Yellow catfish, Pelteobagrus fulvidraco, is one of the most important freshwater aquaculture species in China, but little is known about its genes related to immune response. The present study cloned cDNA encoding TGF-β1 from P. fulvidraco. The results showed the full-length cDNA of TGF-β1 is 2,816 bp and encodes 461 amino acids. The homology of P. fulvidraco TGF-β1 depicted 83% and 81% similarity to the TGF-β1 in Stegastes partitus and Pundamilia nyererei respectively. The phylogenetic tree construction revealed that P. fulvidraco is closely related to Astyanax mexicanus. Analysis of mRNA expression of TGF-β1 in different tissues (gonads, brain, liver, kidney, spleen, intestine, blood, gills, muscle and heart) revealed that TGF-β1 is predominantly expressed in liver and brain, followed by gill and spleen. TGF-β1 gene in gill and spleen up-regulated for 48h after Edwardsiella ictaluri and Flavobacterium columnare injection, then the expression showed a significant decrease (p<0.05). These results indicated that TGF-β1 contributes to the inherent immune reaction of P. fulvidraco.