Lipid acquisition and retention in tissues of spawning adult paddlefish Polyodon spathula (Walbaum, 1792) in relation to extended and compressed life history patterns in two river‐reservoir systems

Data from recreationally caught adult paddlefish from North Dakota and Oklahoma, USA, was used in an initial attempt to explain variation in lipid content in adult wild paddlefish Polyodon spathula (Walbaum, 1792) by stock and by sex. The objectives of this study were to describe the relative importance of three distinct paddlefish tissues [white muscle, red muscle, and gonadal fat body (GFB)] for lipid storage, and compare lipid content of these tissues between stock and sex. It was hypothesized that lipid content of the three tissue types would be related to each other within individual fish; and that, consistent with previously documented life history differences, lipid concentrations for all tissues would be sex‐ and stock‐specific. Paddlefish were sampled in April and May 2012 from the Grand Lake, Oklahoma, USA (GL) and Yellowstone‐Sakakawea, North Dakota (SAK) stocks. Three tissue types were collected from SAK fish, including white muscle (N = 137; 83M, 54F), red muscle (N = 74; 36M, 38F), and GFB (N = 164; 105M, 59F). Samples from GL fish included white muscle (N = 60; 36M, 24F), and GFB (N = 42; 41M, 1F). Proximate analysis was used to quantify the percentage of lipid, water, ash, and protein in tissue samples. The lipid component of proximate analysis was completed using the ANKOM method of lipid extraction which uses heated petroleum ether to extract lipid. Also investigated were lipid accumulation and storage in adult paddlefish in relation to tissue type: white muscle, red muscle, gonadal fat bodies (GFB) within individual fish, between the sexes, and between the two different stocks. White muscle was significantly correlated with both red muscle and GFB lipid, but red muscle lipid was not significantly correlated with GFB lipid. White muscle lipid content differed by stock and sex, with the more northerly stock having higher lipid content than the more southerly stock. Females had higher white muscle lipid content (SAK F = 17.18, M = 9.09; GL F = 6.74, M = 4.99) and red muscle (SAK F = 47.72, M = 30.93) than males. In contrast, GFB lipid differed by sex but not stock, with females having lower lipid content (SAK = 79.79, GL = 89.08) than males (SAK = 89.08; GL = 91.72). Life history differences, growing season, and the role of metabolism may help explain the differences in concentrations of lipids observed between stocks and between the sexes for all three tissues. It was hypothesized that different tissues may be used for different metabolic processes and that although metabolism likely strongly influences muscle tissue lipid, GFB lipid is probably linked more closely to reproductive demands associated with gonad development.     

An approach for assessing paddlefish Polyodon spathula (Walbaum, 1792) populations using mark‐recapture information

Historically, management of fish populations has been achieved through the use of age‐derived estimates of growth and mortality. For long‐lived species such as the paddlefish, Polyodon spathula, the validation of calcified structures is necessary to correct for the presence of false annuli or the absence of growth rings. Regardless, numerous studies on paddlefish populations throughout their range have continued the use of un‐validated age estimates to evaluate dynamic rate functions. The use of mark‐recapture studies has been applied widely to evaluate growth of short‐lived fishes, but only recently to a few long‐lived freshwater fishes (i.e. white sturgeon, shovelnose sturgeon, and pallid sturgeon). This study provides the first simultaneous evaluation of both mark‐recapture and age‐estimate information in determining population characteristics for paddlefish. In doing so, this study has determined that the P. spathula population in the Black River below Clearwater Dam, Missouri is sustainable. Additionally, mark‐recapture information is sufficient to produce accurate and reliable assessments of paddlefish populations in lieu of validated aging structures; future management should be centered on accurate scientific methods, which is not the case when using un‐validated aging structures (e.g. scales, otoliths, fin rays, dentary bones) to determine population parameters. Mark‐recapture information can provide an accurate, alternative source of growth and mortality information for use in evaluating and managing paddlefish populations throughout their range.     

Comparative precision of age estimates from two southern reservoir populations of paddlefish [Polyodon spathula (Walbaum, 1792)]

The aim of the study was to determine whether location and sex affected the age precision estimates between two southern, reservoir populations of paddlefish [Polyodon spathula (Walbaum, 1792)]. From 589 paddlefish collected in Grand Lake and Keystone Lake, Oklahoma in 2011, ages from dentaries were estimated using three independent readers and precision was compared with coefficient of variation between locations and sexes. Ages were more precisely estimated from Grand Lake and from females.     

Comparison of growth performance,biochemical and fatty acid compositions between all‐female diploid and triploid rainbow trout Oncorhynchus mykiss (Walbaum, 1792)

This study compares the performance (in terms of survival and growth), biochemical and fatty acid compositions among all female diploid (AFD) and triploid (AFT) rainbow trout (Oncorhynchus mykiss). AFD and AFT fish with mean initial weights of 1,040.1 ± 1.3 and 1,039.7 ± 1.6 g, respectively, were reared and fed from March to August with a commercially extruded trout feed in a commercial freshwater fishfarm located in the Black Sea region (Samsun, Turkey). Survival was reduced throughout the experimental period in the AFT group with increasing water temperatures. At the end of the experiment, survival rates were 98.57 ± 1.43% and 82.38 ± 7.39% for the AFD and AFT groups, respectively. The AFD group showed significantly better growth performances in terms of weight gain, feed conversion rate (FCR), relative growth rate (RGR) and specific growth rate (SGR) than the AFT group (p < .05). Significantly less protein and greater fat content were also observed in the AFT group (p < .05). There was no significant difference between groups for fatty acid composition in meat, except for stearic acid (SA, C18:0) and docosahexaenoic acid (DHA, 22:6 n‐3). While the greatest SA concentration was in the AFT group, the greatest DHA concentration was observed in the AFD group (p < .05). The results indicate that female triploid rainbow trout are more susceptible to suboptimal environmental conditions (especially to higher water temperatures) than female diploids. Although poor triploid performance was observed in this study, relative productivity might be enhanced by rearing triploids in optimal environmental conditions.     

The effects of different cycles of starvation and re‐feeding on growth and body composition in rainbow trout (Oncorhynchus mykiss,Walbaum, 1792)

This study was designed to investigate the effects of starvation and re‐feeding cycles on the growth performance and body chemical composition of Oncorhynchus mykiss juveniles. A total of 360 juveniles with initial mean weights (IW) of 8.46 ± 0.07 g (n = 360) were stocked into 400‐L tanks in triplicate for each group, with 30 juveniles per tanks. The control group received regular feed, as is the common practice. The three other groups were periodically starved: 1 day starvation followed by 6 days re‐feeding (S1), 2 days starvation followed by 5 days re‐feeding (S2) and 3 days starvation followed by 4 days re‐feeding (S3). The experiment lasted for 10 weeks, over the course of which the water flow rate was 4 L min^?1 and the water quality parameters determined as: temperature 14.4 ± 1.1°C, oxygen 8.2 ± 0.4 mg L^?1 and pH 7.5 ± 0.2. At the end of the study, S1 had the best growth performance (final weight, specific growth rate, average daily growth) of all test groups (P < 0.05). The lowest daily feed intake (DFI) and growth performance parameters were observed in S3 (P < 0.05), while protein efficiency ratio (PER), net protein utilization (NPU) and lipid efficiency ratio (LER) were higher in the S3 fish group than in the other groups (P < 0.05). Whole body protein and lipid contents were highest in S1 fish. The hepatosomatic index (HSI) and viscerosomatic index (VSI) were significantly different among groups (P < 0.05). Feed conversion ratio (FCR) was significantly lower in starvation groups S1, S2 and S3 than in the control (P < 0.05). Compensation coefficient (CC) values were higher than 1 in all starvation groups. The concluding indicate that rainbow trout exposed to 1 and 2 days of starvation in week cycles could achieve over compensation compared to the control. Additionally, partial growth compensation and improved feed utilization could be achieved in a starvation group within 3 days in a week, by beginning with the juvenile size over a 10‐week experimental period.