ABSTRACT In an attempt to better understand the problems in weaning larval fish to artificial die... more ABSTRACT In an attempt to better understand the problems in weaning larval fish to artificial diets, our lab has begun to investigate the role of the digestive hormone cholecystokinin (CCK). While there are a number of other labs also investigating CCK and other digestive hormones such as bombesin, PPY, and gastrin; research into the roles of these hormones in fish is still in its infancy. Previous research with red drum larvae suggests that some component of rotifers and algae enable red drum larvae to more efficiently utilize microparticulate diets than when these are not included in the culture system. The current study investigated the impact of soluble components of rotifers and algae on the CCK and trypsin responses of larval red drum at 6 and 10 days post hatch (DPH). Introduction of homogenized rotifers was shown to significantly increase whole body CCK levels, CCK mRNA, and trypsin activity in 6 DPH red drum larvae, but not in 10 DPH larvae. Homogenates of Isochrysis galbana did not significantly affect CCK or trypsin at either age. This research suggests that there is a soluble component of rotifers that can upregulate digestive function in larval red drum, at least in 6 DPH larvae. Webb, K. and J. Holt 2008. Cholecystokinin and Trypsin Responses of Larval Red Drum (Sciaenops Ocellatus) to Soluble Components of Rotifers (Brachionus Plicatilis) and Algae (Isochrysis Galbana). 79-89 pp. Editores: L.
ABSTRACT Effect of replacing dietary fish oil with vegetable oils on the fatty acid composition o... more ABSTRACT Effect of replacing dietary fish oil with vegetable oils on the fatty acid composition of muscle tissue of juvenile California halibut (Paralichthys californicus) Efecto de sustituir el aceite de pescado dietético con aceites vegetales en la composición de ácidos grasos del tejido muscular de juveniles de lenguado de California (Paralichthys californicus) ABSTRACT. Total replacement of cod liver oil by vegetable oils in the diets of juvenile California halibut (Paralichthys californicus) was analyzed. Five diets were formulated with olive oil, corn oil, linseed oil, and two combinations of linseed oil and corn oil, and compared with a control diet containing cod liver oil during a 12-week feeding experiment. Highest growth was observed in fish fed the control diet; however, no significant differences in growth and survival were observed among the dietary treatments. The fatty acids from linseed, corn, and olive oils were the most accumulated in the tissue, increasing in proportion to the total fatty acids. Reduced levels of 20:5n-3 and 20:4n-6 in the presence of high dietary levels of 18:3n-3 and 18:2n-6 suggest that, as in most marine fishes, synthesis of 18:3n-3 to 20:5n-3 and of 18:2n-6 to 20:4n-6 is either very limited or does not occur. Although the content of 22:6n-3 in the muscle of fish fed the control diet was approximately 2.0 to 2.5 times greater than that in the muscle tissue of fish fed the experimental diets, no significant differences were detected. A proportional decrease in 20:5n-3 among all fatty acids and a lack of an increase in body tissue suggest that this fatty acid was being used to synthesize 22:6n-3. The significant reductions in the level of 20:5n-3 indicate that if the experiment had been conducted over a longer period of time, a level would eventually be reached whereby the dietary deficiency would presumably be reflected by an adverse effect on growth. Additional research is needed, particularly regarding the proportional and quantitative changes of 20:5n-3 and 22:6n-3 in the composition of the muscle tissue.
ABSTRACT The totoaba (Totoaba macdonaldi) is an endemic marine fish of the Sciaenidae family that... more ABSTRACT The totoaba (Totoaba macdonaldi) is an endemic marine fish of the Sciaenidae family that has been overfished to the risk of extinction, and after three decades of protection and preliminary culture results, it is now considered an excellent candidate for commercial aquaculture due to its fast growth and good adaptation to culture conditions. However, as with most marine fish species, larval culture and adequate weaning are still one of the main bottlenecks to successful commercial production. Thus, the objective of this study was to evaluate weaning success of totoaba larvae onto a microdiet at various stages of development utilizing growth, survival and condition factor as response variables. Weaning onto a microdiet was evaluated at 17 (17 W), 22 (22 W) and 27 (27 W) days post-hatch (DPH). At the end of the experiment (35 DPH), growth was significantly higher (i.e., two-fold increase) in the weaned treatments compared to their respective controls (i.e., feed with live prey exclusively), except for the 22 W treatment that resulted in no significant differences. Comparing final weight and final length among the different weaned treatments did not result in any significant differences. However, survival rate was significantly lower in the weaned treatments compared to their control groups. Although the experiment was not design to quantitatively evaluate cannibalism, this behavior was observed towards the end of the weaning trial and may have a significant contribution to the mortality observed in the weaned treatments. Based on these results and despite of the lower survival, it appears that totoaba larvae possess a sufficiently developed digestive system as early as 17 DPH and can be weaned onto commercial diets before the stomach is fully functional. Thus, it is possible to perform an early weaning (17 DPH) in totoaba larvae, as a strategy to reduce juvenile production costs and increase profitability of the production system, by reducing the use of Artemia nauplii without affecting growth.
The temporal evolution of chymotrypsin activity during early ontogeny of laboratory reared red dr... more The temporal evolution of chymotrypsin activity during early ontogeny of laboratory reared red drum larvae was accomplished using a combination of biochemical assays and electrophoretic methods (substrate SDS-PAGE). Optimal functional conditions for chymotrypsin were also determined. Chymotrypsin activity was first detected prior to the onset of exogenous feeding. Total chymotrypsin activity increased with age and standard length. Specific activity was
Medium chain triglycerides (MCT), mostly C6–C12, are physiologically active compounds which are r... more Medium chain triglycerides (MCT), mostly C6–C12, are physiologically active compounds which are readily absorbed, transported and appear to be preferentially utilized as an energy source but are not deposited in lipid stores in a variety of terrestrial animals. Consequently, the incorporation of MCT in feeds may allow the utilization of higher levels of lipids, possibly increasing protein sparing, without affecting
ABSTRACT Four diets were formulated to evaluate the partial to total substitution of fishmeal wit... more ABSTRACT Four diets were formulated to evaluate the partial to total substitution of fishmeal with poultry by-product meal (PBM) (0, 33, 67 and 100PBM) in diets for totoaba juveniles (Totoaba macdonaldi). Amino acid profiles from diets and fatty acid content in diets and muscle tissue were used to assess the fish performance using PBM as fishmeal replacement. Stable isotopes of nitrogen (δ15N) were measured in muscle and liver tissue to quantify the retention of each protein source. At the end of the experimental period, the fish fed the 67PBM diet had a significantly higher growth gain increase compared to the other treatments (almost 2000% over an 86 days period; TGC of 1.06). The total replacement of fishmeal with PBM led to low growth gain increase (ca. 220% over 72 days; TGC of 0.52) and increased mortality. Both fish performance and tissues' fatty acid composition suggest that the 100PBM diet was deficient in essential fatty acids. An isotope-mixing model applied to isotope ratios of muscle and liver tissues of fish fed the 67PBM tissues indicated that PBM was retained into muscle and liver tissue in a higher proportion than its level of inclusion in the diet. We conclude that PBM is a good source of nutrients for totoaba juveniles when used in up to 67% fishmeal replacement level in diets containing 52% protein leading to adequate growth rate and survival.
The leopard grouper is an endemic species of the Mexican Pacific with an important commercial fis... more The leopard grouper is an endemic species of the Mexican Pacific with an important commercial fishery and good aquaculture potential. In order to assess the digestive capacity of this species during the larval period and aid in the formulation of adequate weaning diets, this study aimed to characterize the ontogeny of digestive enzymes during development of the digestive system. Digestive enzymes trypsin, chymotrypsin, acid protease, leucine-alanine peptidase, alkaline phosphatase, aminopeptidase N, lipase, amylase and maltase were quantified in larvae fed live prey and weaned onto a formulated microdiet at 31 days after hatching (DAH) and compared with fasting larvae. Enzyme activity for trypsin, lipase and amylase were detected before the opening of the mouth and the onset of exogenous feeding, indicating a precocious development of the digestive system that has been described in many fish species. The intracellular enzyme activity of leucine-alanine peptidase was high during the first days of development, with a tendency to decrease as larvae developed, reaching undetectable levels at the end of the experimental period. In contrast, activities of enzymes located in the intestinal brush border (i.e., aminopeptidase and alkaline phosphatase) were low at the start of exogenous feeding but progressively increased with larval development, indicating the gradual maturation of the digestive system. Based on our results, we conclude that leopard grouper larvae possess a functional digestive system at hatching and before the onset of exogenous feeding. The significant increase in the activity of trypsin, lipase, amylase and acid protease between 30 and 40 DAH suggests that larvae of this species can be successfully weaned onto microdiets during this period.
ABSTRACT Three sources of soybean meal (SBM) were biochemically characterized and evaluated in di... more ABSTRACT Three sources of soybean meal (SBM) were biochemically characterized and evaluated in diets for juvenile Litopenaeus vannamei. Three biological techniques were utilized to evaluate the nutritional quality of the meals including an outdoor growth trial as well as determination of in vivo apparent digestibility and in vitro digestibility including pepsin digestibility (0.0002%), pH Stat degree of hydrolysis, and immobilized digestive enzyme assay (IDEA). The growth trial was conducted over a 10-wk period using soybean meal as the primary protein source with each meal being included at 54–58% of the diet based on an equal protein inclusion. At the conclusion of the growth trial there were no significant differences between the test diets indicating equivalent biological availability under practical conditions. The in vivo digestibility trial utilized chromic oxide as the inert marker and 70:30 replacement techniques resulted in typical results. Apparent protein digestibility (APD) and apparent energy digestibility (AED) of the diets ranged from 66.8 to 80.2% and 65.4 to 74.7%, respectively. Ingredient digestibility values for protein and energy ranged from 78.8 to 93.5% and 60.5 to 85.0%, respectively. One of the three SBM evaluated had numerically lower protein digestibility and significantly lower energy digestibility than the other two meals.
ABSTRACT In an attempt to better understand the problems in weaning larval fish to artificial die... more ABSTRACT In an attempt to better understand the problems in weaning larval fish to artificial diets, our lab has begun to investigate the role of the digestive hormone cholecystokinin (CCK). While there are a number of other labs also investigating CCK and other digestive hormones such as bombesin, PPY, and gastrin; research into the roles of these hormones in fish is still in its infancy. Previous research with red drum larvae suggests that some component of rotifers and algae enable red drum larvae to more efficiently utilize microparticulate diets than when these are not included in the culture system. The current study investigated the impact of soluble components of rotifers and algae on the CCK and trypsin responses of larval red drum at 6 and 10 days post hatch (DPH). Introduction of homogenized rotifers was shown to significantly increase whole body CCK levels, CCK mRNA, and trypsin activity in 6 DPH red drum larvae, but not in 10 DPH larvae. Homogenates of Isochrysis galbana did not significantly affect CCK or trypsin at either age. This research suggests that there is a soluble component of rotifers that can upregulate digestive function in larval red drum, at least in 6 DPH larvae. Webb, K. and J. Holt 2008. Cholecystokinin and Trypsin Responses of Larval Red Drum (Sciaenops Ocellatus) to Soluble Components of Rotifers (Brachionus Plicatilis) and Algae (Isochrysis Galbana). 79-89 pp. Editores: L.
ABSTRACT Effect of replacing dietary fish oil with vegetable oils on the fatty acid composition o... more ABSTRACT Effect of replacing dietary fish oil with vegetable oils on the fatty acid composition of muscle tissue of juvenile California halibut (Paralichthys californicus) Efecto de sustituir el aceite de pescado dietético con aceites vegetales en la composición de ácidos grasos del tejido muscular de juveniles de lenguado de California (Paralichthys californicus) ABSTRACT. Total replacement of cod liver oil by vegetable oils in the diets of juvenile California halibut (Paralichthys californicus) was analyzed. Five diets were formulated with olive oil, corn oil, linseed oil, and two combinations of linseed oil and corn oil, and compared with a control diet containing cod liver oil during a 12-week feeding experiment. Highest growth was observed in fish fed the control diet; however, no significant differences in growth and survival were observed among the dietary treatments. The fatty acids from linseed, corn, and olive oils were the most accumulated in the tissue, increasing in proportion to the total fatty acids. Reduced levels of 20:5n-3 and 20:4n-6 in the presence of high dietary levels of 18:3n-3 and 18:2n-6 suggest that, as in most marine fishes, synthesis of 18:3n-3 to 20:5n-3 and of 18:2n-6 to 20:4n-6 is either very limited or does not occur. Although the content of 22:6n-3 in the muscle of fish fed the control diet was approximately 2.0 to 2.5 times greater than that in the muscle tissue of fish fed the experimental diets, no significant differences were detected. A proportional decrease in 20:5n-3 among all fatty acids and a lack of an increase in body tissue suggest that this fatty acid was being used to synthesize 22:6n-3. The significant reductions in the level of 20:5n-3 indicate that if the experiment had been conducted over a longer period of time, a level would eventually be reached whereby the dietary deficiency would presumably be reflected by an adverse effect on growth. Additional research is needed, particularly regarding the proportional and quantitative changes of 20:5n-3 and 22:6n-3 in the composition of the muscle tissue.
ABSTRACT The totoaba (Totoaba macdonaldi) is an endemic marine fish of the Sciaenidae family that... more ABSTRACT The totoaba (Totoaba macdonaldi) is an endemic marine fish of the Sciaenidae family that has been overfished to the risk of extinction, and after three decades of protection and preliminary culture results, it is now considered an excellent candidate for commercial aquaculture due to its fast growth and good adaptation to culture conditions. However, as with most marine fish species, larval culture and adequate weaning are still one of the main bottlenecks to successful commercial production. Thus, the objective of this study was to evaluate weaning success of totoaba larvae onto a microdiet at various stages of development utilizing growth, survival and condition factor as response variables. Weaning onto a microdiet was evaluated at 17 (17 W), 22 (22 W) and 27 (27 W) days post-hatch (DPH). At the end of the experiment (35 DPH), growth was significantly higher (i.e., two-fold increase) in the weaned treatments compared to their respective controls (i.e., feed with live prey exclusively), except for the 22 W treatment that resulted in no significant differences. Comparing final weight and final length among the different weaned treatments did not result in any significant differences. However, survival rate was significantly lower in the weaned treatments compared to their control groups. Although the experiment was not design to quantitatively evaluate cannibalism, this behavior was observed towards the end of the weaning trial and may have a significant contribution to the mortality observed in the weaned treatments. Based on these results and despite of the lower survival, it appears that totoaba larvae possess a sufficiently developed digestive system as early as 17 DPH and can be weaned onto commercial diets before the stomach is fully functional. Thus, it is possible to perform an early weaning (17 DPH) in totoaba larvae, as a strategy to reduce juvenile production costs and increase profitability of the production system, by reducing the use of Artemia nauplii without affecting growth.
The temporal evolution of chymotrypsin activity during early ontogeny of laboratory reared red dr... more The temporal evolution of chymotrypsin activity during early ontogeny of laboratory reared red drum larvae was accomplished using a combination of biochemical assays and electrophoretic methods (substrate SDS-PAGE). Optimal functional conditions for chymotrypsin were also determined. Chymotrypsin activity was first detected prior to the onset of exogenous feeding. Total chymotrypsin activity increased with age and standard length. Specific activity was
Medium chain triglycerides (MCT), mostly C6–C12, are physiologically active compounds which are r... more Medium chain triglycerides (MCT), mostly C6–C12, are physiologically active compounds which are readily absorbed, transported and appear to be preferentially utilized as an energy source but are not deposited in lipid stores in a variety of terrestrial animals. Consequently, the incorporation of MCT in feeds may allow the utilization of higher levels of lipids, possibly increasing protein sparing, without affecting
ABSTRACT Four diets were formulated to evaluate the partial to total substitution of fishmeal wit... more ABSTRACT Four diets were formulated to evaluate the partial to total substitution of fishmeal with poultry by-product meal (PBM) (0, 33, 67 and 100PBM) in diets for totoaba juveniles (Totoaba macdonaldi). Amino acid profiles from diets and fatty acid content in diets and muscle tissue were used to assess the fish performance using PBM as fishmeal replacement. Stable isotopes of nitrogen (δ15N) were measured in muscle and liver tissue to quantify the retention of each protein source. At the end of the experimental period, the fish fed the 67PBM diet had a significantly higher growth gain increase compared to the other treatments (almost 2000% over an 86 days period; TGC of 1.06). The total replacement of fishmeal with PBM led to low growth gain increase (ca. 220% over 72 days; TGC of 0.52) and increased mortality. Both fish performance and tissues' fatty acid composition suggest that the 100PBM diet was deficient in essential fatty acids. An isotope-mixing model applied to isotope ratios of muscle and liver tissues of fish fed the 67PBM tissues indicated that PBM was retained into muscle and liver tissue in a higher proportion than its level of inclusion in the diet. We conclude that PBM is a good source of nutrients for totoaba juveniles when used in up to 67% fishmeal replacement level in diets containing 52% protein leading to adequate growth rate and survival.
The leopard grouper is an endemic species of the Mexican Pacific with an important commercial fis... more The leopard grouper is an endemic species of the Mexican Pacific with an important commercial fishery and good aquaculture potential. In order to assess the digestive capacity of this species during the larval period and aid in the formulation of adequate weaning diets, this study aimed to characterize the ontogeny of digestive enzymes during development of the digestive system. Digestive enzymes trypsin, chymotrypsin, acid protease, leucine-alanine peptidase, alkaline phosphatase, aminopeptidase N, lipase, amylase and maltase were quantified in larvae fed live prey and weaned onto a formulated microdiet at 31 days after hatching (DAH) and compared with fasting larvae. Enzyme activity for trypsin, lipase and amylase were detected before the opening of the mouth and the onset of exogenous feeding, indicating a precocious development of the digestive system that has been described in many fish species. The intracellular enzyme activity of leucine-alanine peptidase was high during the first days of development, with a tendency to decrease as larvae developed, reaching undetectable levels at the end of the experimental period. In contrast, activities of enzymes located in the intestinal brush border (i.e., aminopeptidase and alkaline phosphatase) were low at the start of exogenous feeding but progressively increased with larval development, indicating the gradual maturation of the digestive system. Based on our results, we conclude that leopard grouper larvae possess a functional digestive system at hatching and before the onset of exogenous feeding. The significant increase in the activity of trypsin, lipase, amylase and acid protease between 30 and 40 DAH suggests that larvae of this species can be successfully weaned onto microdiets during this period.
ABSTRACT Three sources of soybean meal (SBM) were biochemically characterized and evaluated in di... more ABSTRACT Three sources of soybean meal (SBM) were biochemically characterized and evaluated in diets for juvenile Litopenaeus vannamei. Three biological techniques were utilized to evaluate the nutritional quality of the meals including an outdoor growth trial as well as determination of in vivo apparent digestibility and in vitro digestibility including pepsin digestibility (0.0002%), pH Stat degree of hydrolysis, and immobilized digestive enzyme assay (IDEA). The growth trial was conducted over a 10-wk period using soybean meal as the primary protein source with each meal being included at 54–58% of the diet based on an equal protein inclusion. At the conclusion of the growth trial there were no significant differences between the test diets indicating equivalent biological availability under practical conditions. The in vivo digestibility trial utilized chromic oxide as the inert marker and 70:30 replacement techniques resulted in typical results. Apparent protein digestibility (APD) and apparent energy digestibility (AED) of the diets ranged from 66.8 to 80.2% and 65.4 to 74.7%, respectively. Ingredient digestibility values for protein and energy ranged from 78.8 to 93.5% and 60.5 to 85.0%, respectively. One of the three SBM evaluated had numerically lower protein digestibility and significantly lower energy digestibility than the other two meals.
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