Country‐wide analysis of large wood as a driver of fish abundance in Swedish streams: Which species benefit and where?

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Efficiency of producing bioflocs with aquaculture waste by using poly-β-hydroxybutyric acid as a carbon source in suspended growth bioreactors

With additional organic carbon, fish waste can be used as a substrate to produce bioflocs, a protein source for aquaculture animals. In choosing a carbon source, one should consider convenience, cost and biodegradability. This study investigates the efficiency of poly-β-hydroxybutyric acid (PHB), a biologically degradable polymer, as a carbon source to produce bioflocs in suspended growth bioreactors (SGRs), PHB-SGRs, compared with glucose (GLU-SGRs). The C:N ratio in PHB-SGRs could be maintained around 15:1. The volatile suspended solids (VSS) yield was 2.94 ± 0.72 gVSS/g fish waste for PHB-SGRS and 4.90 ± 0.23 gVSS/g fish waste for GLU-SGRs. The recycling rate of nitrogen in aquaculture solid waste was 56 ± 2% and 87 ± 7% for the PHB-SGRs and Glu-SGRs. No significant differences were found in the bioflocs produced and in the crude protein content of the produced bioflocs between PHB-SGRs and GLU-SGRs. PHB-SGRs and GLU-SGRs could remove dissolved inorganic nitrogen from aquaculture wastewater, with average values of 11.82 ± 8.95 and 16.27 ± 3.95 mg/g TSS/d. Because the calculation of the added amount of carbon and the multiple additions of carbon was avoided, PHB is considered to be a good choice as an organic carbon source for this process, even though not all parameters used for assessment were better than those of GLU-SGRs.     

Tartrate resistant acid phosphatase as a marker for scale resorption in rainbow trout,Oncorhynchus mykiss: effects of estradiol-17β treatment and refeeding

In teleosts, a considerable part of the body calcium is found in the scales. Associated with the scales are osteoblasts and osteoclasts, and during periods of high calcium demand such as during sexual maturation or starvation, the scales can be resorbed and thereby act as an internal calcium reservoir. In mammalian bone tissue, the activity of an acid phosphatase (ACP) isoenzyme, tartrate resistant acid phosphatase (TRACP), can be used as a marker for osteoclastic activity. In the present study, an evaluation of TRACP as a marker for osteoclastic activity in teleost scales has been performed. ACP and TRACP was histologically localized at resorption sites around the edge of the scales as well as at resorption holes in the scales. The optimal conditions for biochemical measurements of ACP and TRACP activity were found to be pH 5.3, 10 mM paranitrophenylphosphate, incubated for 30 min at room temperature, and 10 mM tartrate added when required. Using TRACP as a marker, estradiol-17 (E₂) was found to increase the proportion of scales being resorbed, as well as the number and size of resorption sites per scale. Also, the scales of E₂-treated fish showed weaker staining for calcium. Together, the obtained data indicate that estradiol-17 induces osteoclastic activity in teleost scales, resulting in increased resorption of the scales. A period of refeeding following a period of starvation did not have detectable effects on the scale osteoclastic activity and scale resorption.     

Essential fatty acid deficiency in freshwater fish: the effects of linoleic, α-linolenic, γ-linolenic and stearidonic acids on the metabolism of [1-14C]18:3n-3 in a carp cell culture model

The desaturation of [1-¹⁴C]18:3n-3 to 20:5n-3 and 22:6n-3 is enhanced in an essential fatty acid deficient cell line (EPC-EFAD) in comparison with the parent cell line (EPC) from carp. In the present study, the effects of competing, unlabeled C₁₈ polyunsaturated fatty acids (PUFA), linoleic (18:2n-6), -linolenic (18:3n-3), -linolenic (18:3n-6) and stearidonic (18:4n-3) acids, on the metabolism of [1-¹⁴C]18:3n-3 were investigated in EPC-EFAD cells in comparison with EPC cells. The incorporation of [1-¹⁴C]18:3n-3 in both cell lines was significantly reduced by competing C₁₈ PUFA, with the rank order being 18:4n-3>18:3n-3 = 18:2n-6>18:3n-6. In the absence of competing PUFA, radioactivity from [1-¹⁴C]18:3n-3 in EPC cells was predominantly recovered in phosphatidylethanolamine followed by phosphatidylcholine. This pattern was unaffected by competing n-6PUFA, but n-3PUFA reversed this pattern as did essential fatty acid deficiency in the presence of all competing PUFA. The altered lipid class distribution was most pronounced in cells supplemented with 18:4n-3. Competing C₁₈ PUFA significantly decreased the proportions of radioactivity recovered in 22:6n-3, pentaene and tetraene products, with the proportions of radioactivity recovered in 18:3n-3 and 20:3n-3 increased, in both cell lines. However, the inhibitory effect of competing C₁₈ PUFA on the desaturation of [1-¹⁴C]18:3n-3 was significantly greater in EPC-EFAD cells. The magnitude of the inhibitory effects of C₁₈ PUFA on [1-¹⁴C]18:3n-3 desaturation was dependent upon the specific fatty acid with the rank order being 18:4n-3>18:3n-3>18:2n-6, with 18:3n-6 having little inhibitory effect on the metabolism of [1-¹⁴C]18:3n-3 in EPC cells. The differential effects of the C₁₈ PUFA on [1-¹⁴C]18:3n-3 metabolism were consistent with mass competition in combination with increased desaturation activity in EPC-EFAD cells and the known substrate fatty acid specificities of desaturase enzymes. However, the mechanism underpinning the greater efficacy with which the unlabeled C₁₈PUFA competed with [1-¹⁴C]18:3n-3 in the desaturation pathway in EPC-EFAD cells was unclear.