A study was conducted to evaluate the effects of organic acid salt blend (OAB), protease complex (Pr) and their combination (OAB+Pr) in fish meal‐free diets on growth, nutrient retention and digestibility of tilapia. Five diets were designed: a positive control (PC) diet containing 80 g/kg fish meal (FM), a negative control (NC) diet containing 0 g/kg FM and 104 g/kg meat and bone meal, and three other diets supplemented with OAB (922 mg/kg), Pr (175 mg/kg) and OAB+Pr (922 mg/kg + 175 mg/kg) to the NC diet. Tilapia with an initial body weight of 7.0 ± 0.2 g were fed the five diets for 9 weeks. The results showed that the growth performance, nutrient digestibility and retention of NC group had the lowest values among groups. Weight gain of fish fed the OAB and OAB+Pr diets was higher, and feed conversion ratio was lower (p < 0.05) compared to those fed the NC diet, while no differences with those fed the PC diet. The digestibility of dry matter, crude protein, minerals and protein retention was improved in fish fed the OAB+Pr diet (p < 0.05), but not in those fed OAB or Pr diet (p > 0.05). There were no differences in whole‐body composition and lipid retention among the treatments (p > 0.05). The supplementation of OAB and Pr alone or combined significantly increased the villi height but not the width when compared to the NC group. It can be concluded that dietary supplementation of OAB+Pr in a fish meal‐free diet improves growth and nutrient digestibility in tilapia compared to those fed the fish meal‐free diet.

The objective of this study was to compare the supplemental effects of crystalline DLmethionine (DL-Met) and methionine hydroxy analogue calcium (MHA-Ca) on growth performance of Pacific white shrimp. Eight isoproteinic (355.3 ± 2.0 g/kg diet) and isolipidic (70.0 ± 2.2 g/kg diet) diets were prepared as positive diet (20% fish meal), negative diet (15% fish meal) and DL-Met, MHA-Ca-supplemented diets with the supplementation of 0.03%, 0.06%, 0.09% DL-Met and 0.04%, 0.07%, 0.1% MHA-Ca in negative diet respectively. Pacific white shrimp (0.92 ± 0.03 g) were fed one of the eight diets for 49 days. The results showed that dietary DL-Met did not affect weight gain (WG) and feed conversion ratio (FCR) (p > 0.05), but the supplementation of 0.1% MHA-Ca significantly increased WG, protein and lipid retention, and reduced FCR (p < 0.05) when compared to the negative group, and reached the similar levels as the positive control. The total free amino acids (TFAA) in haemolymph of MHA-Ca groups and PC, NC group peaked at the 3rd hr after feeding, but the peaking time of DL-Met groups was advanced to the 2nd hr. Activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in haemolymph of all MHA-Ca groups peaked at the 2nd hr, but DL-Met groups peaked at the 1st hr after feeding. The above results indicated that the supplementation of 0.1% MHA-Ca in a low fish meal diet could improve the growth performance and feed utilization of Pacific white shrimp, but dietary DL-Met did not significantly affect the growth.

Eight isolipidic diets containing 0, 20, 40, and 60 g/kg oxidized fish oil (OFO) or oxidized soybean oil (OSO) were fed to triplicate groups of channel catfish, Ictalurus punctatus, for 8 weeks to investigate the effects of oxidized oils on growth, body color, and antioxidative capacity. Lower weight gain (WG) was observed in fish fed high levels of oxidized oils (40 and 60 g/kg) (p < .05). At the inclusion of 40 g/kg, OFO group showed lower WG than the OSO group (p < .05). With the increase of dietary oxidized oils, the serum levels of malondialdehyde, total bilirubin, direct bilirubin, and activity of alanine aminotransferase and aspartate aminotransferase significantly increased (p < .05), but the glutathione level decreased (p < .05). Serum superoxide dismutase and catalase activity showed the maximum values at 20 g/kg OFO group and 40 g/kg OSO group, respectively. Compared to the 0 g/kg oxidized oil groups, both dietary oxidized oils increased the b* value (yellowness) of dorsal skin and caudal skin at 40 and 60 g/kg inclusion (p < .05). In conclusion, dietary oxidized oil (≥40 g/kg) decreased the growth and the antioxidative capacity and increased the yellowness of skin. OFO caused more negative effects on channel catfish than OSO at the inclusion of 40 g/kg.

The cover image, by Xiao‐Qin Li et al., is based on the original article Organic acid salts, protease and their combination in fish meal‐free diets improved growth, nutrient retention and digestibility of tilapia (Oreochromis niloticus × O. aureus). DOI: .