Search

Fish show variation in feeding habits to adapt to complex environments. However, the genetic basis of feeding preference and the corresponding metabolic strategies that differentiate feeding habits remain elusive. Here, by comparing the whole genome of a typical carnivorous fish (Leiocassis longirostrisGu¨nther) with that of herbivorous fish, we identify 250 genes through both positive selection and rapid evolution, including taste receptor taste receptor type 1 member 3(tas1r3) and trypsin. We demonstrate that tas1r3is required for carnivore preference in tas1r3-deficient zebrafish and in a diet-shifted grass carp model. We confirm that trypsin correlates with the metabolic strategies of fish with distinct feeding habits. Furthermore, marked alterations in trypsin activity and metabolic profiles are accompanied by a transition of feeding preference in tas1r3-deficient zebrafish and diet-shifted grass carp. Our results reveal a conserved adaptation between feeding preference and corresponding metabolic strategies in fish, and provide novel insights into the adaptation of feeding habits over the evolution course.

A high carbohydrate diet (HCD) induced excessive hepatic de novolipogenesis, which caused metabolic disorder and impaired the health of fish species. Betulinic acid (BA) has been applied to ameliorate fatty liver and anti-inflammatory in mammals. Here, we investigated the effects of dietary BA supplementation on HCD-induced hepatic de novolipogenesis and liver health in channel catfish (Ictalurus punctatus). The catfish were fed with three diets: NCD (18% carbohydrate), HCD (36% carbohydrate), HCD+BA (36% carbohydrate with 150mg/kg BA). After an 8-week feeding trial, we found that dietary BA decreased hepatosomatic index (HSI) and condition factor (CF) without affecting the growth of channel catfish fed HCD. Dietary BA significantly reduced the HCD-induced excessive lipid accumulation (oil red O area, TG content, and de novolipogenesis gene expression, P< 0.05). Moreover, we found that dietary BA prevented hepatic lipid accumulation via activating phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and inhibiting sterol regulatory element-binding protein 1 (SREBP1) (P< 0.05) in liver of channel catfish fed HCD. Besides, we also found that dietary BA significantly prevented HCD-induced liver damage, as confirmed by liver H&E staining, reduced inflammation biomarkers (ALT, AST, hydroxyproline, α-smaand tgf-1β), downregulated expression of ER stress-related genes (eif2a, bip, atf4, xbp1) (P< 0.05). Overall, the present study indicated that dietary BA inclusion attenuated hepatic de novolipogenesis, improved liver inflammation and reduced ER stress in channel catfish fed HCD.

Chlorellameal is a potential protein source for aquafeeds. However, the physiological response of carnivorous fish fed Chlorellameal remains elusive. This study evaluated the effects of replacing dietary fish meal with Chlorellameal on growth performance, pigmentation, and liver health in largemouth bass. Five diets were formulated to replace dietary fish meal of 0% (C0, control), 25% (C25), 50% (C50), 75% (C75), and 100% (C100) with Chlorellameal, respectively. Total 300 fish (17.6 ± 0.03 g) were randomly assigned to 15 tanks (3 tanks/group). Fish were fed the experimental diet twice daily for 8 weeks. The increased dietary Chlorellameal quadratically influenced the final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), and feed intake (FI), which were significantly lower in the C100 group than in the other groups (P < 0.05). The feed conversion ratio (FCR) increased linearly or quadratically with dietary Chlorellameal. Dietary Chlorellameal linearly or quadratically increased the lutein content of plasma, liver, and dorsal muscle of largemouth bass (P < 0.05). Compared to the C0 group, all supplemented Chlorellameal groups significantly improved the yellowness (b∗) of the dorsal body (1.5 to 2.0 fold), abdominal body (1.5 to 1.8 fold), and dorsal muscle (3.8 to 5.4 fold) of largemouth bass (P < 0.05). In addition, compared to the C0 group, the liver vacuolation area of fish was significantly increased in the C75 and C100 groups (P < 0.05). Transcriptional levels of apoptosis-related genes of β-cell lymphoma-2 (bcl2),caspase-9-like (casp9),and caspase-3a (casp3) were markedly upregulated (0.9 to 1.6 fold) in the C100 group compared to the C0 group (P < 0.05). Based on the quadratic regression analysis between FBW, WGR, or SGR and dietary Chlorellameal level, largemouth bass had the best growth when replacing 31.7 to 32.6% of fish meal with 15.03 to 15.43% dietary Chlorellameal. The present results indicated that dietary supplementation with Chlorellameal (11.85 to 47.45%) significantly enhanced the pigmentation; however, total replacement of fish meal (40%) with Chlorellameal (47.45%) caused growth retardation, apoptosis, and liver damage in largemouth bass.