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The present study was aimed at investigating the interactive effects of starvation and dietary lipid level in the previous feeding period on lipid-related composition of turbot. Turbot with an average initial body weight of 26 g were firstly fed diets with different lipid levels, namely, 8%, 12%, and 16%, for 9 weeks, and then subjected to starvation for 30 days. Each diet was fed to sextuplicate tanks of 35 fish in the feeding trial. Tissue samples were collected at the end of the feeding trial and at 10, 20, and 30 days after starvation. The results showed that 30-day starvation decreased the lipid content in the liver and the subcutaneous tissue around the fin (STF), but increased the lipid content in the muscle. A synergetic increase of muscle lipid by starvation and dietary lipid level was observed. Starvation mobilized different fatty acids among the three tissues, namely, MUFA (16:1n-7 and 18:1n-9) in the muscle, SFA (14:0 and 16:0), MUFA (16:1n-7, 18:1n-9 and 20:1n-9), and 18C-PUFA (18:2n-6 and 18:3n-3) in the liver, and unexpectedly n-3 PUFA (18:3n-3, EPA, and DHA) in the STF, respectively. The 30-day starvation decreased the muscle hardness and resilience, but affected other texture parameters in a starvation time-dependent manner. Up-regulation of expression of lipolytic genes by starvation occurred later in the STF than in the liver. Interactive effects of starvation and dietary lipid level were observed mainly on tissue fatty acid compositions. Results of this study suggested that combined manipulation of starvation time and dietary lipid level could be used as an effective means of fish quality regulation in terms of lipid/fatty acid-related composition., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

A 9-week feeding trial was conducted to investigate the effects of different dietary sources of astaxanthin on fillet coloration, texture, and nutrient composition in rainbow trout (Oncorhynchus mykiss). Eight diets were formulated to contain 0, 25, 50, 75, 100, and 125 mg/kg astaxanthin from wall-broken Haematococcus pluvialis (WBHPA), 100 mg/kg astaxanthin from wall-unbroken H. pluvialis (WUHPA), or chemically synthesized astaxanthin (CSA). Each diet was fed to triplicate groups of rainbow trout (mean initial weight of 561 g) twice daily (07:00 and 17:00) to apparent satiation for 9 weeks. Results showed that at the 100 mg/kg astaxanthin inclusion level, the CAS group had higher fillet gross energy, dorsal fillet redness, and dorsal fillet color card score compared to the WBHPA-100 group, with both being higher than the WUHPA group (P < 0.05). Fillet astaxanthin content, dorsal fillet yellowness, and lateral line redness and yellowness did not differ significantly between the CSA and WBHPA-100 groups (P > 0.05), but were higher than the WUHPA group. When WBHPA was used, the inclusion of 50–100 mg/kg decreased fillet lightness but increased fillet redness, while better fillet texture was served at 75–125 mg/kg. Dietary 25–125 mg/kg WBHPA inclusion increased fillet astaxanthin and gross energy concentrations, with minor effects on fatty acid compositions of fillet. Inclusion of over 100 mg/kg astaxanthin regardless of source decreased fillet threonine and serine contents, and the WBHPA-100 group had lower fillet glycine and alanine contents compared to the control group (P < 0.05). In conclusion, CSA had the most significant impact on fillet coloration and energy deposition in rainbow trout, while WUHPA had the least favorable effect. Additionally, the wall-breaking treatment of H. pluvialis can improve the effect of astaxanthin on fillet coloration and nutrient composition in rainbow trout, with a recommended dose range of 75–100 mg/kg. [ABSTRACT FROM AUTHOR]

Simple Summary: The supply of fish oil, which provides long-chain polyunsaturated fatty acids (LC-PUFA) but is mostly wild-caught, is stagnating, resulting in limited availability and high prices. Therefore, many alternative lipid sources, mainly vegetable oils and rendered animal fats, are increasingly being applied in fish feeds. However, these lipid sources do not contain LC-PUFA, and therefore lower the fillet quality in terms of the LC-PUFA content. Feeding strategies such as alternate feeding between fish oil- and alternative oils-based diets have been applied to maintain the n-3 LC-PUFA contents in farmed fish. The present study validated the relevant efficacy. A 12-week feeding experiment was conducted to evaluate the effects of replacing fish oil (FO) with beef tallow (BT) on the fatty acid composition of farmed tiger puffer (Takifugu rubripes). Two replacement strategies were used: a standard Graded Dietary Replacement of FO with BT (GDR strategy) and Alternate Feeding between FO- and BT-based Diets (AFD strategy). The positive and negative control diets were formulated with 6% FO (FO-C group) or BT (BT-C group) as the sole added lipid source. In the GDR strategy, three experimental diets were formulated, with 25, 50 and 75% of the added FO in the FO-C diet replaced with BT, named 25BT, 50BT and 75BT, respectively. In the AFD strategy, alternated feeding patterns between the FO-C and BT-C diet—namely, 1, 2 and 3 weeks with BT-C followed by 1 week feeding with FO-C (1BT-1FO, 2BT-1FO and 3BT-1FO, respectively)—were applied. Each diet or feeding strategy was assigned to triplicate tanks. The results showed that dietary BT inclusion reduced the contents of long-chain polyunsaturated fatty acids (LC-PUFA) in both the muscle and liver (edible tissues for this species) of the experimental fish, and the liver displayed a more drastic decrease than the muscle. The LC-PUFA content linearly decreased with the decreasing dietary FO levels in the GDR strategy. However, in the AFD strategy, a linear relationship was not observed between the LC-PUFA content and the FO feeding duration. The 3BT-1FO treatment resulted in higher LC-PUFA content than 2BT-1FO. When comparing the two strategies with the same final FO administration level—namely, 50BT vs. 1BT-1FO, and in particular, 75BT vs. 3BT-1FO—the AFD strategy resulted in higher LC-PUFA contents in both the muscle and liver than the GDR strategy. In conclusion, when FO was replaced with BT in the diets, alternate feeding between FO- and BT-based diets resulted in a higher LC-PUFA content than the standard direct replacement. Three weeks of feeding with BT-C followed by one week of feeding with FO-C appeared to be a good alternate feeding pattern. This study provided a promising strategy of FO-sparing in fish farming when the LC-PUFA contents were maintained as high as possible. [ABSTRACT FROM AUTHOR]