The effect of feeding rate on growth of pectoral fin spine of juvenile great sturgeon Huso huso (Linnaeus, 1758)

The effect of two feeding rates (0.5 and 1.5% of total body weight) was assessed on the growth of pectoral fin spines of captive juvenile great sturgeon, Huso huso, after second year of life. The fish received Oxytetracycline (OTC) twice in the first and second years of their lives under basic diet. During the 5‐month experimental period, juveniles (mean 1,187.4 g, 0.1 standard deviation [SD]), n = 50) were reared with two feeding rates under similar conditions in 10 fiberglass tanks (1.5 m³). The fish were fed manually with a commercial diet twice a day (35% Biomar, Nersac, France) throughout the experiment. The OTC marks were distinguished in all pectoral fin spine sections under ultraviolet light. The means of the first and second annular radii were 806.6 µm (27.2 SD) and 2,246.5 µm (50.2 SD), respectively. The marginal increment analysis beyond the second OTC mark revealed a significantly smaller marginal increment for low feeding rate treatment (143.9, 11.2 SD) as compared to the high feeding rate one (269.0, 14.6 SD). The results indicate the slower growth rate in the fish fed the low feeding treatments seen in the pectoral fin spine formation, which can be used as an indicator of recent feeding history in sturgeon juveniles. The best daily feeding rate for great sturgeon of 2,460 g was determined to be 1.5% body weight/day in this study.     

A comparative study of feeding methods: Effect on the growth,behaviour and biochemical performance of juvenile Beluga sturgeon (Huso huso Linnaeus, 1758)

This study compared the influence of feeding methods on growth parameters of young‐of‐year Beluga sturgeon Huso huso in a 6‐week trial. Fish with an average weight 150.3 ± 0.8 g (±SE) were stocked into nine circular concrete tanks (30 fish per tank) in an open circular system with water temperature of 18.9°C. All fish were fed by three different feeding methods: (a) hand‐fed (HF), (b) continuously available (automated feeder; AF), (c) half of daily feed provided by hand, and another half by automated feeder (combined feeding). For the hand‐feeding method, fish were fed at 09:00, 14:00, 19:00, and 24:00. The entire automatic feeding groups were fed with the same amount of feed. The mean final body weight was the highest in fish fed by AF compared to fish fed by HF. Body weight increase, condition factor, specific growth rate, and feed conversion ratio did not differ among the feeding groups. Fish fed by AF revealed higher swimming activity than the HF group. No significant changes were found in hematocrit, glucose and total protein concentrations among treatments. The results showed less dependence of growth and physiology of Beluga sturgeon on feeding method, but automated‐feeding was shown to be suitable for sturgeon rearing because of further low labour costs in rearing systems.     

Effects of dietary prebiotic GroBiotic®‐A on growth performance,plasma thyroid hormones and mucosal immunity of great sturgeon,Huso huso (Linnaeus, 1758)

The present study was conducted to evaluate the effects of Grobiotic^®‐A, a commercial prebiotics, when administered in feed on the growth performance, plasma thyroid hormones and mucosal immunity of great sturgeon (Huso huso). The commercial prebiotic mixture was supplemented in the diets at four different levels (i.e. 0.0% as control, 0.5%, 1% and 2%, in three replicates, 20 fish per replicate) and fed to the fish for an 8‐week period wherein 240 fish were cultured in 1,800‐L fiberglass tanks that formed part of a flow‐through system. Water temperature was maintained at 20.4 ± 1.5°C. Significant changes in growth performance parameters were observed, but only in those groups fed with 1% and 2% prebiotics. Specifically, marked improvements relative to the control group were observed in percentage weight gain, body weight gain, feed conversion ratio and specific growth rate in prebiotic‐fed fish. The levels of plasma thyroid hormones, specifically thyroxine and thyroid stimulating hormones were significantly elevated in the group receiving 2% prebiotics. Activities of lysozyme and alkaline phosphatase in skin mucus were significantly enhanced in prebiotics‐fed groups, particularly at an inclusion level of 1% and higher (2% group compared to the control). Inhibitory activity of the skin mucus against pathogens, particularly Streptococcus iniae and Yersinia ruckeri, was significantly improved following prebiotic feeding. Taken together, dietary inclusion of GroBiotic^®‐A promoted growth, modulated thyroid hormones, and enhanced mucosal immunity of H. huso. This prebiotic mixture has the potential for use in improving the growth performance and health status of farmed great sturgeon.     

Endocrine changes during the previtellogenic stage of the great sturgeon,Huso huso (Linnaeus, 1758)

The study aimed to investigate changes in serum concentrations of sex steroids, thyroid hormones, stress indices, cholesterol, triacylglycerol, calcium and phosphorus, as well as the growth in the 3‐year old previtellogenic stage of great sturgeon, Huso huso over a 6‐month period. Forty individually marked fish (mean weight 6913 g) were divided among three circular tanks under a natural temperature and photoperiod. Every 1.5 months fish were weighed and blood samples taken for serum analysis. Fish showed significant changes in 17β estradiol, testosterone, triiodothyronine (T₃), thyroxine (T₄), adrenocorticotropic hormone, cortisol, cholesterol, and phosphorus, but not in triacylglycerol and calcium concentrations. From the January onset of the experiment to the end of the trial in July, there was a decrease in sex steroids and cortisol concentrations as well as a decline in T₃ concentrations from March and in T₄ from February to July. The mean weight of fish increased significantly from the beginning to the end of the experiment. Although the oocyte diameter increased from 197 to 202 μm, the difference was not significant. The histological data on oocytes suggest that the great sturgeon, like the other sturgeons, has a heterogeneous asynchronous ovarian development in the early stage of reproduction. This data might be useful to the further understanding of the physiology of Huso huso and/or to improve its culture. Moreover, it leads to a general increase in the understanding of the basic reproductive biology of this valuable chondrostean species.     

Production of recombinant great sturgeon (Huso huso,Linnaeus, 1758) growth hormone (GH) by Pichia pastoris (Guillierm, 1956)

In this research, the encoding cDNA of growth hormone (GH) was cloned from the pituitary gland of great sturgeon Huso huso (three adults: two females and one male, 7–9 years old, 70–90 kg, reared in concrete ponds). In order to obtain the great sturgeon recombinant GH expression in Pichia pastoris, the mature encoding cDNA was first cloned in TA vector PTZ57R and then sequenced. After confirmation of the correct GH sequence, the GH coding sequence was subcloned into pHILS1 expression vector. The yeast Pichia pastoris GS115 strain was transformed with the expression plasmid. Results obtained from this study showed that great sturgeon GH recombinants were expressed upon induction with methanol and exported into the medium. The level of expression was examined using RNA analysis, SDS‐PAGE, and western blot analysis. RNA analysis of the recombinant strains showed a sharp, specific band in 800 bp. The specific band in transformants indicated the presence of GH RNA in the yeast. SDS‐PAGE and western blot analysis showed a specific 21 kDa band for the growth hormone. Culture conditions were optimized for pH = 6 and incubation time (after 24 h induction, peaking at 72 h) for maximal protein production. The results provide useful information for the future production of recombinant growth hormones in other sturgeon species.     

Effects of dietary l‐carnitine supplements on growth and body composition in beluga sturgeon (Huso huso) juveniles

The effects of dietary l ‐carnitine on growth performance, whole body composition and feed utilization were studied in beluga, Huso huso. Fish were randomly allocated in 15 tanks (30 fish per tank) and triplicate groups were fed to satiety during 84 days one of five isonitrogenous (41% CP) and isoenergetic (20 MJ kg^?1) diets, each differing in l ‐carnitine content [0 (control), 300, 600, 900 and 1200 mg kg^?1 diet]. At the end of the trial, fish grew from 19‐ to 23‐fold in weight, from 8.4 g to a maximum of 191 g. Fish fed 300–600 mg l ‐carnitine had the highest specific growth rate (SGR, 3.69 and 3.72% day^?1) and protein efficiency ratio (PER, 0.95 and 0.99), and the lowest feed conversion ratio (FCR, 1.4 and 1.3) than the other groups (P < 0.0001). SGR, PER and FCR were the poorest for fish fed 1200 mg l ‐carnitine, while fish fed the unsupplemented and 900 mg l ‐carnitine supplemented diet showed intermediate performance. Body lipid concentration decreased significantly from 5.8 to 5.1% (P < 0.0001) with dietary l ‐carnitine supplementation increasing from 0 to 300 mg. Energy content was significantly lower in fish fed the 900 and 1200 mg l ‐carnitine diet (5.8 MJ kg^?1), when compared with the other treatment groups (6.4–6.6 MJ kg^?1). The results indicated that feeding sturgeon on diets supplemented with 300 mg l ‐carnitine kg^?1 diet improved growth performance, and stimulated protein‐sparing effects from lipids.     

Effect of prebiotic mannan oligosaccharide on hematological and blood serum biochemical parameters of cultured juvenile great sturgeon (Huso huso Linnaeus, 1754)

The nutritional effects of prebiotic mannan oligosaccharide were evaluated using hematological and blood serum biochemical parameters in cultured juvenile great sturgeon (Huso huso). Fish were offered formulated diets containing two levels of prebiotic mannan oligosaccharide (2 and 4 g kg^?1); a basal diet with no prebiotics was used as control. The experiment lasted for 46 days. Blood samples were collected from the caudal veins of 18 apparently healthy fish (average weight 217.77 ± 29.8 g) at the end of the trial. No significant differences were found in the serum enzyme activity levels between treatments (P > 0.05). However, adding mannan oligosaccharide as a supplement to the basal diet resulted in significant differences in lymphocytes and eosinophils between the control and the 2 g kg^?1 treatment (P < 0.05) as well as a significant difference in the creatinine factor in the 2 g kg^?1 mannan oligosaccharide treatment (P < 0.05). The results show that it would be advantageous to add 2 g kg^?1 mannan oligosaccharide to the diets of juvenile great beluga sturgeon (Huso huso).     

Measures of immune system status in young‐of‐the‐year winter flounder Pseudopleuronectes americanus

The immune status of young‐of‐the‐year (YOY) winter flounder Pseudopleuronectes americanus was evaluated in fish collected from six areas around Long Island, NY, U.S.A. representing more urban areas with high population density in the west, to less densely populated more rural areas in to the east. Gene expression markers for innate immunity (pleurocidin) and contaminant exposure (cytochrome P4501A; cyp1a) were measured in liver and fin of fish collected at each site. Expression of pleurocidin was significantly higher in fin than liver, but was highly variable among individuals. Some statistically significant differences in pleurocidin expression among sites were observed, although elevated levels were not associated with degree of urbanization. Expression was related in part to fish size: a positive correlation between expression and total length (L_T) of fish was observed with the largest L_T class (>125 mm) exhibiting significantly elevated pleurocidin expression as compared with fish in the smaller L_T class. This indicates that immune competency may increase with age. No site‐specific differences in cyp1a expression were observed. These data suggest that exposure to aromatic hydrocarbon contaminants is fairly widespread throughout the study area and that any differences in pleurocidin expression in YOY P. americanus are probably due to other factors. Antimicrobial activity was also measured as a functional indicator of immune response. Activity was highly variable, showing no significant site‐specific differences, and no significant correlation to pleurocidin expression. The lack of correlation between pleurocidin expression and antimicrobial activity indicates that other antimicrobial peptides may be active against the bacteria tested or that other factors are influencing antimicrobial activity. This is the first quantitative evaluation of pleurocidin expression in YOY P. americanus from an urban area. Further work is needed to characterize factors controlling pleurocidin expression, as well as other indicators of immune response in young fish.     

Identification of young‐of‐the‐year great hammerhead shark Sphyrna mokarran in northern Florida and South Carolina

Two sharks, visually identified in the field as young‐of‐the‐year (YOY) scalloped hammerhead Sphyrna lewini, were identified as great hammerhead Sphyrna mokarran based on nuclear‐encoded single nucleotide polymorphisms (SNP) and sequences of mtDNA. Individuals were captured and released in Bulls Bay, SC, and Saint Joseph Bay, FL, in 2013 and 2014, respectively. These findings indicate S. mokarran may be pupping in or around these areas and highlight new regions that may be a productive focus for future research on early life history of S. mokarran.     

Effect of starvation and re‐feeding on growth performance and content of plasma lipids,glucose and insulin in cultured juvenile Persian sturgeon (Acipenser persicus Borodin, 1897)

The effect of starvation and subsequent re‐feeding to satiation on compensatory growth performance, insulin and blood serum values were investigated in juvenile Persian sturgeon (Acipencer persicus) with an average weight 108.04 ± 0.28 g (mean ± SEM) and in the same rearing condition over an 8‐week period. Sturgeons were allocated to one of five feeding treatments: controls (C, continuous feeding), W1 (1 week starvation), W2 (2 weeks starvation), W3 (3 weeks starvation) and W4 (4 weeks starvation), followed by a single 4 weeks of re‐feeding to satiation. Changes in growth performance and blood serum indices were examined at the end of weeks 4 and 8. Body weight, specific growth rate (SGR), condition factor (CF) and weight gain were determined to have significantly decreased during starvation. Fish starved for 1 week reached the same weight as the control fish after re‐feeding for 4 weeks, indicating that complete compensatory growth occurred. Although the specific growth rate in W2, W3 and W4 fish was greater than that in the control fish after re‐feeding, W2, W3 and W4 fish did not reach the same body weight as control fish at the end of re‐feeding period, and showed partial compensation only. Blood plasma, glucose and insulin concentrations did not change significantly during starvation and re‐feeding (P > 0.05). This suggests that sturgeon are able to maintain glycaemia during starvation, probably due to their non‐carbohydrate dietary source. Plasma total lipid and triglyceride levels increased in starvation treatments, whereas the increases were significant only in W3 treatment (P < 0.05). After a 4‐week re‐feeding period, their levels decreased in comparison to the starvation periods. Increases in plasma total lipid and triglyceride levels appear to be due to their roles as preferred nutrients for mobilization in Persian sturgeon and the magnitude and duration of compensatory growth depended on the length of food deprivation.     

Eelgrass,Zostera marina,as essential fish habitat for young‐of‐the‐year winter flounder,Pseudopleuronectes americanus (Walbaum, 1792) in Maine estuaries

Distribution and density by habitat for age‐0, young‐of‐the‐year (YOY) winter flounder, Pseudopleuronectes americanus (Walbaum, 1792), were compared for two Maine estuaries to help define essential fish habitat for this life history stage. Two estuaries (Weskeag River and Penobscot Bay) along Mid‐coast Maine were sampled monthly with daytime 1.0 m² fixed‐frame throw traps around neap low tide, May–December over two consecutive years (2003–2004). Both eelgrass and adjacent sand/mud (20–60 cm deep) were randomly sampled with equal effort (4–12 samples per month) at two sites in both the Weskeag River and Penobscot Bay. Significantly higher densities of YOY winter flounder (2–9 cm TL) occurred in eelgrass relative to sand/mud. Density increased significantly in both habitats in 2004, and was higher in Penobscot Bay relative to the Weskeag River. YOY densities compared by eelgrass coverage within throw traps were found to be significantly higher in eelgrass that exceeded 30% coverage when compared with adjacent sand/mud areas and eelgrass coverage of 10–20%. YOY occurred in all months sampled (May–December); no density differences existed by month. These results indicate that very shallow (<0.6 m) eelgrass habitat is of key importance to YOY winter flounder in Maine estuaries and should be viewed as essential fish habitat (EFH) for this species and life stage.     

Determination of sex and maturity stage of great sturgeon (Huso huso) using steroid sex hormones profiles,histology and laparoscopic images of gonads

We studied sex and maturity stage of great sturgeon with different reproductive stages using sex steroid hormones concentrations in blood plasma, gonad histology and laparoscopic technique. One hundred sixty farmed great sturgeons at ages between 1 and +12 years and weight ranged from 0.45 to 49.65 kg (80 males and 80 females, 20 fish of each maturity stage) were selected. Mean sex steroid levels showed that testosterone (T) and 11ketotestosterone (11KT) in plasma varied significantly by sex and maturity stage. But the mean concentrations of 17B‐estradiol (E2) varied significantly only between the maturity stages I and III. All fish were sex determined by laparoscopy and histology examinations confirmed it. Our results showed, however laparoscopy was effective method for sex determination at four maturity stages, but young fish at maturity stage I required gonadal histology examinations to confirm sex. The present study results showed that some steroid sex hormones (T and 11KT) can be used to determine sex and reproductive stage in great sturgeon, especially in later maturity stages. Although the laparoscopy may be stressful and cause small scars on the body of the fish, but it is a fast, effective, and cheap method for sex and maturity stage assessment (30 to 40 s for each fish), especially at later maturity stages. Histology of gonads is a very accurate, but it is an invasive method and not a suitable technique for commercial purposes. Histology is more suited for scientific studies than commercial application. The ability to use minimally invasive methods for sex determination will assist broodstock management and conservation in sturgeons.     

Karyotype variability in successive generations after hybridization between the great sturgeon, Huso huso (L.), and the sterlet, Acipenser ruthenus L.

Effects of particle size, fish size and temperature on the filtration rate of silver carp were determined. When feeding at 20°C on zooplankton and spherical particles (yeast, micronic beads and pollen), 32-g silver carp filter particles larger than 70 urn at a maximum rate of 18.251 h⁻¹. For particles smaller than 70 μm, filtration rates decrease with decreasing particle size until there is no measured filtration for particles smaller than 10 μm. Filtering rates ( FR ) for particles between 10 and 50 μm are described by the equation, FR =−20.8 + 21.7 × log particle diameter. Filtration rates rise as fish size, particle size and temperature increase. Filtration rates per unit biomass, however, fall as fish size increases: FR = 1.54 W^0.713, where FR is the maximum filtration rate in ¹ h ¹ fish ¹ and W is weight of fish in grammes. The results of these trials are consistent with the hypothesis that particle selection by silver carp is a mechanical, passive function of gill raker morphology.     

Effect of wave exposure dynamics on gut content mass and growth of young‐of‐the‐year fishes in the littoral zone of lakes

Total length, body mass and gut content mass of young‐of‐the‐year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave‐induced energy flux (E_F) of the respective site and sampling day, while no correlation of gut content mass with E_F was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high E_F. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased E_F. In P. fluviatilis, increased gut content mass during periods of high E_F resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high E_F, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes.