| Feeding trials were conducted in indoor culture system to investigate effects ofdietary carbohydrate level and source on growth performance, apparent digestibilitycoefficient, whole body composition and selected physiology parameters of juvenilecobia (Rachycentron canadum L.) and effects of dietary carbohydrate level and sourceon growth performance, apparent digestibility coefficient, glucose metabolism andexpression of glucose transporters in rainbow trout (Oncorhynchus mykiss),respectively. Results of the present study are presented as follows:1. Six isonitrogenous (43%crude protein) and isolipidic (10%crude lipid) diets,using fish meal and casein as protein sources and fish oil as lipid source, wereformulated to contain graded level of gelatinized corn starch (2.5%,6.5%,12.5%,18.4%,24.2%and30.4%of dry weight, respectively). At the end of9-weekfeeding trial, no significant differences in survival rate were observed amongdietary treatments (P>0.05). Specific growth rate (SGR), feed efficiency ratio(FER) and protein efficiency ratio (PER) increased with increasing dietary starchup to18.4%(P<0.05), and thereafter SGR declined but FER and PER remainednearly the same (P>0.05). Apparent digestibility coefficient (ADC) of starchreduced significantly when dietary starch up to30.4%(P<0.05). Fish fed the dietswith starch from18.4%to30.4%showed higher amylase activities in intestinaltract than those fed diets containing starch1.3%and6.5%(P<0.05). Significantlyhigher whole-body lipid contents were observed in fish fed diets containing higherstarch (P<0.05). Whole-body moisture was inversely correlated with whole-bodylipid content, while protein and ash showed no significant differences (P>0.05).Plasma glucose, hepatosomatic index (HSI), liver glycogen and liver lipidincreased with increasing dietary starch (P<0.05). On the basis of SGR and FER,the appropriate dietary starch supplementations of juvenile cobia were estimatedto be21.1%and18.0%of diet, respectively.2. Seven isonitrogenous (43%crude protein) and isolipidic (10%crude lipid) diets, using fish meal as protein source and fish oil as lipid source, were formulated tocontain20%different carbohydrate source (cellulose, glucose, sucrose, gelatinizedwheat starch, gelatinized corn starch, gelatinized tapioca starch and native cornstarch, respectively). At the end of10-week feeding trial, survival rate wasindependent of dietary carbohydrate source (P>0.05). Lowest SGR and FERwereobserved in fish fed glucose diet (P<0.05). Fish fed the diet containing celluloseor native corn starch showed significantly higher SGR and PER than those fedglucose diet, whereas lower than those fed sucrose or gelatinized starch diet(P<0.05). Fish fed sucrose diet showed lower SGR compared with those fedgelatinized wheat starch diet (P<0.05), and there were no significant differencesamong fish fed diets with sucrose, gelatinized corn starch and gelatinized tapiocastarch (P>0.05). Significantly lower FER was observed in fish fed sucrose dietcompared with those fed gelatinized starch diets (P<0.05). Fish fed gelatinizedwheat starch diet showed highest SGR and FER compared with those fed otherdiets, while there were no significant differences among cobia fed gelatinizedstarch diet (P>0.05). Significantly lower ADC of dry matter was observed in fishfed cellulose or native starch diet than those fed others (P<0.05). Fish fed dietsucrose or glucose diet showed significantly higher ADC of dry matter than thosefed cellulose or native starch diet (P<0.05), whereas lower than those fedgelatinized starch diets (P<0.05). Significantly lower ADC of dietary protein wasfound in fish fed glucose diet than those fed others (P<0.05). Fish fed gelatinizedstarch diet indicated significantly higher ADC of carbohydrate compared withthose fed native starch diet (P<0.05). Fish fed glucose diet showed the highestwhole body moisture among treatments, and lower whole body protein and lipidthan those fed gelatinized starch diets (P<0.05). Lower whole body lipids werefound in fish fed cellulose or native starch diet than those fed gelatinized starchdiets (P<0.05). Lower plasma glucose and hepatic glycogen contents wereobserved in fish fed cellulose, sucrose or native starch diet than those fedgelanized starch diets (P<0.05). The plasma glucose contents increased sharplyafter feeding starch diets and peaked at5h, then decreased. During the first1hourafter feeding starch diets, hepatic glycogen contents decreased, thereafterincreased to the peak at5-7h, then a less rapid decline than plasma glucoseoccurred. Fish fed native starch diet indicated lower plasma glucose and hepaticglycogen contents than those fed gelatinized starch diets at each sampling time (P<0.05). Plasma glucose remained at fasting level in fish fed cellulose dietregardless of time postprandially. These results indicated that gelatinized wheatstarch was optimal carbohydrate source for cobia.3. Three isonitrogenous (46%crude protein) and isolipidic (11%crude lipid) diets,using fish meal as protein source, fish oil and canola oil as lipid sources, wereformulated to contain different carbohydrate level (10%and30%gelatinizedwheat starch) or source (30%glucose and30%gelatinized wheat starch).Throughout the14-week feeding trial, there were no significant differences amongtreatments (P>0.05). SGR was not affected by dietary starch level (P>0.05), butby carbohydrate source, and significantly lower SGR was found in fish fed30%glucose diet than those fed30%starch diet (P>0.05). Fish fed30%starch dietshowed higher PER than those fed10%glucose diet. While lower PER was foundin fish fed the diet with10%starch diet compared with those fed30%starch diet(P<0.05). Rainbow trout fed30%starch diet showed lower ADC of arbohydratethan those fed10%starch diet (P<0.05). Higher whole body lipid content and HSIwere observed in fish fed diets with higher dietary carbohydrate (P<0.05). Fishfed30%glucose diet indicated lower PER than those fed30%starch at5and9weeks (P<0.05), while PER was not affected by carbohydrate source at14weeks(P>0.05). ADC of dry matter in fish fed30%starch diet was significantly higherthan those fed10%starch diet (P<0.05), while lower than those fed30%glucosediet (P<0.05). ADC of crude protein was independent of dietary carbohydratelevel and source (P>0.05). ADC of lipid was not affected by dietary starch level(P>0.05), but by carbohydrate source, and significantly lower ADC of lipid wasfound in fish fed30%glucose than those fed30%starch (P<0.05). ADC of grossenergy in fish fed30%starch diet was significantly higher than those fed10%starch diet (P<0.05), while lower than those fed30%glucose diet (P<0.05). ADCof carbohydrate was not affected by dietary carbohydrate source (P>0.05) but bycarbohydrate level, and significantly lower ADC of carbohydrate was observed infish fed30%starch diet compared with those fed10%starch diet (P<0.05). Wholebody moisture was independent of dietary carbohydrate level and source (P>0.05).Fish fed30%starch diet showed lower whole body protein content than those fed10%starch diet (P<0.05), and there was no significant difference between fish fed30%glucose diet and30%starch diet (P>0.05). Fish fed30%starch diet showedsignificantly higher whole body lipid than those fed10%starch diet or30% glucose diet (P<0.05). Interestingly, for fish fed30%starch diet, plasma glucosewas significant higher than those fed10%starch or30%glucose diet at5weeks(P<0.05), whereas plasma glucose content was independent of dietarycarbohydrate status at9and14weeks (P>0.05). Plasma glucose contents weresignificantly higher at5h postprandially than24h. Significant changes wereobserved in hepatic gene expression over time.(1) Expression of GK had apositive correlation with plasma glucose content and decreased with extendedexperimental period (P<0.05). PFK expression was very low, and significantlylower in fish fed30%starch diet than those fed10%starch diet or30%glucosediet at5weeks (P<0.05), while independent of diet at9and14weeks (P>0.05).Expression of PK was regardless of dietary treatment and experimental time(P>0.05).(2) Expression of PEPCK was independent of diet and experimentaltime (P>0.05). Expression of G6Pase was independent of diet (P>0.05), whilehigher expression was observed at9weeks than5weeks (P<0.05). Experimentaltime did not affect transcription of FBPase (P>0.05), while lower expression wasfound in fish fed30%starch diet compared with those fed10%starch or30%glucose diet (P<0.05).(3) G6PDH expression had a positive correlation with GKand decreased after24h postprandially than5h (P<0.05).(4) Higher expression ofGsase was observed in fish fed30%starch diet than those fed10%starch diet at5weeks (P<0.05), while no significant difference was observed between fish fedtwo diets at9and14weeks (P>0.05). Expression of Gsase was significantlyhigher at5h postprandially than24h (P<0.05). The results suggested to someextent, adaptation to high (30%) level of starch occurred over the extendedexperimental period and the inducibility of expression of hepatic glucosemetabolic enzymes varied at the different samping time/fish size.4. Throughout the feeding trial, transcription of GLUT1was not significantlyaffected by dietary carbohydrate level or source (P>0.05) but by sampling time(P<0.05). Lower expression of GLUT1was observed in fish fed30%starch dietthan those fed30%glucose diet, and higher expression were found at5hpostprandially than24h (P<0.05).(2) Red blood cell: Only GLUT1expressionwas detected in the red blood cell of rainbow trout, and higher at5h after feedingthan24h (P<0.05).(3) White muscle: Expressions of GLUT1and GLUT4weredetected in the while muscle. Expression of GLUT1increased with extendedexperimental period (P<0.05). GLUT4expression was independent of diet (P>0.05). However, significantly higher expression of GLUT4was observed at5h postprandially than24h (P<0.05).(4) Expressions of GLUT1, GLUT2, SGLT1and SGLT2were detected in the kidney of rainbow trout. Expressions of GLUT2,SGLT1and SGLT2affected by diets and showed similar trends as higherexpression at24h postprandially than5h (P<0.05), and higher expression in fishfed30%starch diet than those fed10%starch diet (P<0.05). |
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