Studies on activity, distribution, and zymogram of protease, α-amylase, and lipase in the paddlefish Polyodon spathula

A series of biochemical determination and electrophoretic observations have been conducted to analyze the activities and characteristics of protease, α-amylase, and lipase of paddlefish Polyodon spathula. The results obtained have been compared with those of bighead carp (Aristichthys nobilis) and hybrid sturgeon (Huso dauricus ♀?×?Acipenser schrenki Brandt ♂), in order to increase available knowledge of the physiological characteristics of this sturgeon species and to gain information with regard to its nutrition. Further, a comparative study of enzymatic activity, distribution, and characterization between commercial feed-reared paddlefish (CG) and natural live food-reared (NG) paddlefish was conducted. Results showed that higher proteolytic activity was observed in the pH range 2.5-3.0 and at a pH of 7.0 for paddlefish. Levels of acid protease activity of paddlefish were similar to that of hybrid sturgeon, and significantly higher than that of bighead carp. The inhibition assay of paddlefish showed that the rate of inhibition of tosyl-phenylalanine chloromethyl ketone was approximately 2.6-fold that of tosyl-lysine chloromethyl ketone. There was no significant difference observed for acid protease activity between PG and CG groups, whereas the activity of alkaline protease, α-amylase, and lipase in the PG group were significantly lower than those in the CG group. The substrate sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis further showed that there were certain types of enzymes, especially α-amylase, with similar molecular mass in the paddlefish and hybrid sturgeon. It can be inferred that acid digestion was main mechanism for protein hydrolysis in paddlefish, as reported for other fishes with a stomach. This indicates that the paddlefish requires higher alkaline protease, α-amylase, and lipase activity to digest natural live food.     

LH-β and FSH-β mRNA expression in nesting and post-breeding three-spined stickleback, Gasterosteus aculeatus, and effects of castration on expression of LH-β, FSH-β and spiggin mRNA

The mRNA expression of the LH- and FSH- subunits were measured in nesting and post-breeding male three-spined sticklebacks, Gasterosteus aculetaus, as well as in castrated and sham-operated nesting males. Furthermore, expression of an androgen induced kidney protein, spiggin, and 11-ketotestosterone (11KT) levels, were measured in the castrated and sham-operated males. Nesting males had significantly higher levels of both LH- and FSH- mRNA expression compared to post-breeding males. Furthermore, sham-operated males had significantly higher levels of LH- mRNA and spiggin mRNA expression than the castrated fish. Expression of FSH-, on the other hand, did not differ between castrated and sham-operated males. There were strong positive individual correlations between circulating levels of 11KT on the one hand and expressions of LH- and spiggin mRNA, whereas the correlation between 11KT levels and FSH- mRNA was weak. The negative effect of castration on -LH mRNA indicates that gonadal hormones stimulate this expression, whereas this was not the case for -FSH. The observed decline in -LH expression after the end of the breeding season may be the result of cessation of the gonadal stimulation of the pituitary. On the other hand, it is not likely that this can explain the decline in FSH- expression.     

Influence of 11-ketotestosterone, 17β-estradiol, and 3,5,3′-triiodo-L-thyronine on distribution and metabolism of carotenoids in Arctic charr, Salvelinus alpinus L.*

This investigation examines the influence of implants containing 11-ketotestosterone (11KT), 17-estradiol (E₂), and 3,5,3-triiodo-l-thyronine (T₃) on astaxanthin metabolism in sexually immature individually tagged Arctic charr. The fish (initial average weight 427 g) were maintained in freshwater for 40 days, and weekly implanted intraperitoneally with oil-based injections containing either 11 KT, E₂ or T₃ at levels of 0.1, 1.0 and 0.1 mg (100 g body weight (BW))^–1, respectively. The control fish were given the oil medium alone (0.2 ml 100 g BW^–1). The diet contained ca. 50 mg astaxanthin kg^–1. Carotenoid composition was monitored in plasma, fillet, liver and skin, and 11 KT, E₂ and testosterone (T) levels in plasma. All hormone treatments reduced plasma T compared to the control. E₂-treated fish had a higher (p<0.05) hepatosomatic index (HSI) than the other treatments. Hormone treatment did not influence gonadosomatic index (GSI). T₃ administration induced a silvery skin appearance. The fillet and plasma carotenoid content decreased during the experiment. 11 KT implantation reduced astaxanthin and idoxanthin concentrations of plasma and fillets, and increased the amount in liver and skin, compared to the other treatments. The relative proportion of astaxanthin to idoxanthin was higher in the control fish and T₃ implanted fish, than in fish implanted with 11 KT or E₂ (p<0.05). Fish treated with E₂ had the highest skin carotenoid concentration. Male fish had significantly higher carotenoid content in plasma, fillet and skin than female fish. This study reveals that sex hormones affect carotenoid metabolism and partitioning among body compartments of Arctic charr, effects differently displayed by the sexes.     

Influence of food type,amount, and frequencies on the larviculture of pacamã catfish Lophiosilurus alexandri

This study assessed the performance of L. alexandri postlarvae (2 days after hatching) with different diets (Artemia and Panagrellus redivivus), food amounts (C₃₀₀-C₅₀₀-C₇₀₀), and feeding frequencies (F₁-F₃-F₆) in two experiments lasting 10 days. The best performing food type, Artemia and Artemia with P. redivivus, presented the highest survival rates as well as fish with the greatest weight, length, and specific growth rate (SGR). In the second experiment with Artemia, the weight, length, and SGR presented significant differences, increasing with higher amounts of prey. The best performance was obtained from a daily diet (F₁) with the greatest amount of prey (C₇₀₀).     

Influence of oral administration of estradiol-17β and testosterone on growth,digestion, food conversion and metabolism in the underyearling red sea bream,Chrysophrys major

Estradiol-17 (E2) administered in the diet to the red sea bream Chrysophrys major did not affect appetite, food conversion efficiency, protein efficiency ratio and specific growth rate. Serum concentrations of total protein, albumin, globulin, vitellogenin, -amino acids, total lipid, free fatty acids, cholesterol and calcium were elevated. The hepatosomatic index was also increased. Activities of hepatic enzymes including lactate dehydrogenase, isocitrate dehydrogenase and glutamate-pyruvate transaminase were higher than found in untreated control fish. Intestinal activity of leucine aminopeptidase was augmented. However, there were no changes in muscle water, protein, lipid and glycogen content. In contrast, testosterone (T) given by the same route increased appetite, food conversion efficiency, protein efficiency ratio and specific growth rate. There were no alterations in serum protein and calcium concentrations but serum glucose, ammonia and triglyceride levels were elevated. Hepatic glycogen content was increased. The activities of hepatic fructose- 1,6-diphosphatase, glucose-6-phosphatase and glycogen synthetase and intestinal activities of alkaline phosphatase and -glutamyltransferase were higher than noted on control fish. The results reveal that estradiol-17 and testosterone exerted different metabolic effects in the red sea bream and they suggest that testosterone exerts its anabolic actions by increasing appetite, food conversion efficiency and activities of digestive enzymes.     

Effects of chronic exposure to γ-HCH (Lindane) on brain serotonergic and gabaergic systems,and serum cortisol and thyroxine levels of rainbow trout,Oncorhynchus mykiss

Rainbow trout (Oncorhynchus mykiss) were implanted intraperitoneally with 0.5 ml.100 g^–1 body weight of coconut oil alone (controls) or coconut oil contaning 0.05 mg of -HCH (Lindane). After 18 days, changes in brain serotonin and GABA metabolism, as well as in serum cortisol and thyroxine levels, were measured. A lower final body weight was observed in -HCH treated fish when compared with control fish. No significant differences were found for serum thyroxine levels between control and treated fish, but a significantly higher cortisol level was found in the -HCH-implanted trout. Although GABA levels did not differ significantly in any brain region in the two treatment groups, the activity of the serotonergic system was significantly altered by the pesticide in both the hypothalamus and the telencephalon.     

Effect of Dietary Supplementation of Brewer's Yeast and GroBiotic®-A on Growth,Immune Responses,and Low-Salinity Tolerance of Pacific White Shrimp Litopenaeus vannamei Cultured in Recirculating Systems

Two separate trials were conducted in clean recirculating systems at salinities of 32.9 (optimal) and 2 ppt (low-salinity challenge) to evaluate brewer's yeast and GroBiotic®-A, a commercial prebiotic, as dietary supplements for growth and health management of Pacific white shrimp Litopenaeus vannamei. The growth-promoting influences of brewer's yeast or GroBiotic®-A previously observed with fish were not demonstrated in these trials with shrimp, when each component was supplemented at 2% or 5% of the diet. No significant dietary effects on hematological and immunological responses—including total hemocyte count, hemolymph protein, phenoloxidase, hemocyte respiratory burst, and clearance efficiency of Vibrio harveyi—were observed in shrimp cultured at full strength salinity (30 ppt) in feeding trial 1 after a 10 week period. In a second feeding trial, dietary supplementation of GroBiotic®-A improved survival of shrimp cultured at low-salinity (2 ppt). Although the mechanism(s) for enhanced survival under low-salinity conditions by dietary immunostimulants or prebiotics have not been identified, these observations indicate potential use of prebiotics such as GroBiotic®-A for shrimp cultured in less than optimal environments.     

Habitat and prey selection of common minke,sei, and Bryde’s whales in mesoscale during summer in the subarctic and transition regions of the western North Pacific

This study represents the first quantitative analysis of the characteristics of the distribution areas and stomach contents of common minke whale Balaenoptera acutorostrata, sei whale B. borealis, and Bryde’s whale B. edeni in relation to oceanographic and prey environments in mid summer in the western North Pacific. Common minke whales were distributed within subarctic regions and the northernmost region of the transitional domain, coinciding with the main habitat of their preferred prey, Pacific saury Cololabis saira. Sei whales were mainly found in the northernmost part of the transition zone and showed prey preference for Japanese anchovy Engraulis japonica, which was significantly more abundant in the main distribution area of the whale than in its adjacent areas. “Hot spots” of Bryde’s whales were found in several regions of the transition zone between the subarctic boundary and the Kuroshio front. This whale species preferred Japanese anchovy as prey, for which the distribution density was significantly higher in the main distribution area of the whale than in the adjacent areas. These results indicate that the summer distributions of Pacific saury and Japanese anchovy greatly influence the distributions of these whale species, suggesting that the whales’ habitat selection is closely related to their prey selection.     

Dietary β-Glucan and Nucleotide Effects on Growth,Survival and Immune Responses of Pacific White Shrimp,Litopenaeus vannamei

Effects of dietary supplementation of β-glucans and nucleotides on growth, survival and immune responses of the Pacific white shrimp (Litopenaeus vannamei) at a low salinity (5 ppt) were evaluated during a 30 d feeding trial. Final mean weight of shrimp fed nucleotides at 0.5%?was highest and significantly different from those fed the basal diet or diets supplemented with β-glucans. Survival was significantly higher for shrimp fed the diet with 0.2%?β-glucans compared to all other diets and was lowest for shrimp fed the basal diet. Shrimp fed diets containing β-glucans and nucleotides had generally better immune responses than shrimp fed the basal diet with higher total hemocyte count (THC) recorded for shrimp fed 0.2%?β-glucans followed by those fed 0.2%?nucleotides. Shrimp fed diets with 0.2%?and 0.5%?nucleotides and 0.2%?β-glucans had significantly higher respiratory burst values than shrimp fed the basal diet. These results indicated that dietary supplementation of either nucleotides or β-glucans has beneficial effects in improving shrimp performance when cultured at low salinity.     

Bioaccumulation of hexachlorocyclohexane,dichlorodiphenyltrichloroethane, and estradiol-17β in catfish and carp during the pre-monsoon season in India

This investigation was performed to monitor hexachlorocyclohexane isomers (HCHs), dichlorodiphenyltrichloroethane (DDT, and its metabolites, refered to as DDTs), plasma levels of estradiol-17β (E2), and the gonadosomatic index (GSI) between sampling sites of unpolluted ponds of Gujartal, Jaunpur (control site) and the polluted rivers Gomti (Jaunpur) and Ganga (Varanasi), which affect the reproductive physiology of some edible catfish and carp during the pre-monsoon season. HCHs and DDTs were measured by gas liquid chromatography (GLC) and hormones by radioimmunoassay (RIA). The results indicated that the level of HCHs and DDTs was very high in both the catfish and the carp captured from the polluted rivers compared with the fish captured from the control site. The GSI and E2 values were lower in both groups of fish when compared to the fish from the control site. The results also indicate that catfish showed greater bioaccumulation of HCHs and DDTs than carp, above the permissible limit, as compared to the fish from the control site. In conclusion, fish from the Gomti and Ganga rivers were highly polluted when compared with fish from the control site, as was evident from high levels of tissue bioaccumulation of HCHs and DDTs and decreased levels of plasma E2, inhibiting the reproductive physiology of these species at the receptor level. The levels exceeded the maximum residue limits (MRL) as recommended by Codex, hence it is suggested that the fish should be avoided for food purposes.     

Physicochemical and Microbiological Assessment of Ready-to-Eat Tuna Döner Kebab During Marination,Cooking, and Different Storage Conditions

ABSTRACT

The aim of this work was to investigate the use of bluefin tuna (Thunnus thynnus) in ready-to-eat döner kebab production and determine the effects of marination, cooking, and storage conditions (4 and ?18°C) on physicochemical and microbiological properties of döner kebab. The raw tuna meat and raw, cooked, and stored döner kebab samples were subjected to moisture, protein, fat, ash, pH, cholesterol, biogenic amines, lipid oxidation, fatty acids profile, microbiological, and sensory analysis. The major fatty acids in tuna döner kebab were palmitic, stearic, oleic, omega-3, and omega-6 fatty acids; unsaturated fatty acids were higher than saturated fatty acids (p < 0.05). Low biogenic amine and cholesterol contents were determined in döner kebab. While cooking affected the proximate composition, microbial load, and the levels of histamine and tyramine (p < 0.05), marination did not have any significant effect. The study results indicated that using tuna meat in döner kebab production could be an alternative approach to provide new seafood products without posing any acceptability problems in terms of quality factors.     

Turnover of α-, γ, and δtocopherol and distribution insubcellular and lipoprotein fractions indicate presence of an hepatic tocopherolbinding protein in Atlantic salmon (Salmo salar L.)

The purpose of this work was to study the turnover of a, andtocopherol (TOH) in Atlantic salmon (Salmo salar, L.). Fish induplicate tanks were fed a diet containing 150 mg kg^-1-TOH and 100 mg kg^-1 each of and TOHadded as tocopheryl acetates. After fillet TOH concentrations had adjustedto the dietary supplementation levels, samples were taken from fish that hadbeen deprived of feed for 100 h, and from fish that had been fed regularlyuntil sampling. The retained levels of tocopherols in plasma correspondedgrossly with their biological activities, as found in experiments withmammals (::100: 20:3). The plasma concentrationsof -, and TOH amounted to 65, 44 and 15%,respectively, in unfed compared to fed fish. Very low density lipoprotein(VLDL), appeared to contain a greater fraction of plasma -TOH than ofplasma TOH. The mitochondrial fraction of liver, but not that of darkmuscle, was highly enriched in -TOH, and less in andTOH. The concentration ratios in liver and bile indicate that, and to some extent, TOH are excreted in the bile at a higherrate than -TOH. The data fit the hypothesis that Atlantic salmonliver contains a tocopherol binding protein with higher affinity for-TOH than for the other tocopherol homologues. This appears toprevent excretion of -TOH in the bile, and stimulate incorporation of-TOH in VLDL for subsequent secretion into the blood stream. As aconsequence, -TOH is retained in the body to a greater extent than and -TOH.     

Molecular and phenotypic characterization of Vibrio aestuarianus, a pathogen of the cultured tongue sole, Cynoglossus semilaevis Günther

Studies were conducted to determine the cause of high mortalities of cultured half-smooth tongue sole Cynoglossus semilaevis. Gross signs of disease included loss of appetite, erratic swimming, and haemorrhages on the head, opercula and base of fins, dorsal fin rot, swollen abdomen filled with ascitic fluid and herniation of the intestine. Histological examination of the liver showed focal areas of necrosis and extensive haemorrhages. Virtually pure, dense bacterial cultures were obtained from liver, kidney and spleen tissues, and high pathogenicity of the isolates to tongue sole was confirmed. The phenotypic characteristics of the isolates including morphological, physiological and biochemical characteristics were determined. The 16S rRNA and gyrB genes of the isolates were sequenced, and the phylogenetic trees representing genetic relatedness between the isolate and publicly available 16S rRNA and gyrB gene sequences from GenBank were constructed. The results confirmed that the diseased tongue soles were infected with Vibrio aestuarianus. The sequenced 16S rRNA gene of strain TS1 (GenBank Accession No. GQ372983) was 1446bp, the gyrB gene of strain TS1 (GenBank Accession No. GQ372984) was 1200bp and the two genes exhibited high similarity (98~99%) to those of V. aestuarianus from GenBank. In addition, the activities of extracellular enzymes and haemolysin were also studied; the results showed that the isolates produced beta haemolysis on rabbit blood agar, lecithinase, proteinase, DNase and lipase, but gelatinase was not produced.     

Factors affecting the catch and harvest rates of paddlefish downstream of Gavins Point Dam,South Dakota, 2000–2020

Paddlefish, Polyodon spathula (Walbaum), provide an important snagging and bowfishing fishery below Gavins Point Dam in South Dakota. During 2009–2020, snagging catch rates of paddlefish decreased below Gavins Point Dam to presumed “normal” lower pre-2004 levels, while bowfishing catch (harvest) rates significantly increased during 2000–2020. Because Paddlefish are highly migratory, both local (i.e., monthly gauge height, precipitation, and air temperature near Gavins Point Dam) and remote (difference in Mississippi and Missouri River discharge near their confluence) environmental conditions were used to explain variation in snagging catch rates and bowfishing harvest rates. Snagging catch rates were related to October gauge height, whereby deeper water in October led to decreased catch rates below Gavins Point Dam. Bowfishing harvest rates increased significantly after a 2016 regulation change moved the season from July 1 to July 31, and from June 1 to June 30, likely because water clarity was greater in June than in July. Mean annual air temperature and precipitation explained variation in bowfishing harvest rates prior to the 2016 regulation change. Our findings, the first to examine both snagging and bowfishing fisheries below Gavins Point Dam, suggest that local abiotic factors are likely more important than remote discharge for explaining variation in snagging catch rates and bowfishing harvest rates in the channelised Missouri River.     

Temporal dynamic and economic valuation of recreational fisheries of the lower Cuiabá River,Brazilian Pantanal

Fisheries are the most common ecosystem service that fish provide to human populations, yet recreational fisheries are often overlooked when evaluating such services. Here, the socioeconomic profiles of fishers, the composition of their catches and catch per unit effort (CPUE) are described, to estimate the economic value of the recreational fishery on a stretch of the Cuiabá River in the Brazilian Pantanal. Questionnaires were used to obtain socioeconomic information and fishing yield from fishers for 2013 and 2014. Additionally, a census on the number of fishers and fishing platforms along the sampled region was conducted in 2018. This recreational fishery mostly involves middle class adult males, based mostly in the Cuiabá city metropolitan region. They invested, on average, US$41.1 (SD = US$16.5, median = $35.2) per fishing visit, catching around 19 fish species. Overall, mean CPUE from the recreational fishery was 42.20 fish/fisher.day (17.4 kg/fisher/day). Annual economic value of this recreational fishery was estimated at around US$1.8 million, which highlights the importance of this activity to the local economy. Greater environmental conservation efforts are recommend to ensure the long-term viability of this ecosystem service.     

Demonstration of primary cilia and acetylated α-tubulin in fish endothelial,epithelial and fibroblast cell lines

Primary cilia (PC) were demonstrated for the first time in fish endothelial, epithelial and fibroblast cell lines through immunofluorescence staining with the monoclonal antibody, 6-11B-1, against acetylated α-tubulin. The study was carried out with eight recently developed cell lines from the walleye, Sander vitreus (Mitchill). These were three fibroblast-like cell lines, WE-cfin11f, WE-skin11f and WE-liver3 from, respectively, the caudal fin, skin and liver, and three epithelial-like cell lines, WE-cfin11e, WE-spleen6 and WErpe from, respectively, the caudal fin, spleen and retina. Also, endothelial-like WEBA from the bulbus arteriosus and glial-like WE-brain5 from the brain were used. Immunocytochemistry revealed strong staining for acetylated α-tubulin in mitotic spindles and midbodies for all cell lines, and in PC for all cell lines except WE-skin11f. Staining of cytoplasmic microtubules (fibrils) was absent in three cell lines, including WEBA, but present in the others, especially WE-skin11f, which might have obscured PC detection in these cells. Tubacin, an inhibitor of histone deacetylase 6, induced cytoplasmic fibrils in WEBA and the intensity of their staining in WE-cfin11f. These results suggest that the cell lines might differ in their deacetylase activities, making them useful for studying this tubulin modification in teleosts, as well as for studying PC.     

Hypothermal effects on expression of regucalcin,a calcium-binding protein,in the livers of seawater- and fresh water–acclimated milkfish,Chanos chanos

Fish Physiology and Biochemistry - Regucalcin (RGN) is a calcium-binding protein mainly expressed in the liver. It functions in regulating activities of several calcium-dependent enzymes related to...     

The influence of temperature, dietary polyunsaturated fatty acids, α-tocopherol and spermine on fatty acid composition and indices of oxidative stress in juvenile Arctic char, Salvelinus alpinus (L.)

Juvenile Arctic char, Salvelinus alpinus (L.), were fed two levels of polyunsaturated fatty acids (PUFA) (5.5 or 2.5% of diet (37 or 16% of lipid respectively)), -tocopheryl acetate (70 or 300 mg kg–1 diet) and the antioxidant spermine (0 or 250 mg kg–1 diet) in a 3×2 factorial design and analysed for tissue fatty acid composition and indices of oxidative stress. The effect of temperature was evaluated by first maintaining the fish at 12 °C for 70 days and then 0.6 °C for 71 days. Liver and muscle fatty acid compositions were significantly influenced by the fatty acid compositions of the feed, although extensive modification of some fatty acids took place prior to deposition in the tissues. Maintaining char at low temperature increased liver PUFA content particularly in fish fed the low PUFA diets while no major changes were seen in muscle. Tissue - tocopherol deposition was mainly influenced by dietary - tocopheryl acetate. Dietary spermine had no influence on tissue levels of spermine. Dietary manipulation had no major influence on haematology and blood chemistry. High dietary PUFA increased the content of thiobarbituric acid reactive substances (TBARS) in both liver and muscle. Neither -tocopheryl acetate nor spermine influenced tissue TBARS content. Lowering the environmental temperature influenced several parameters including haematology, blood chemistry and muscle spermine content, but none were related to diet. It is concluded that Arctic char is tolerant to a wide range of dietary content of PUFA (16 to 37% of lipid) and - tocopherol (70 to 300 mg kg–1), and that spermine offers no further protection against oxidative stress. It is suggested that toxic levels of PUFA is related to the amount in dietary lipid where more than 50% of lipid may be harmful to the fish.     

Effects of salinity, dietary level of protein and 17α-methyltestosterone on growth hormone (GH) and prolactin (tPRL177 and tPRL188) levels in the tilapia, Oreochromis mossambicus

In the present study, we examined the long-term effects of environmental salinity, diet (35% and 25% crude protein) and 17-methyltestosterone (MT) on corresponding levels of pituitary and serum growth hormone (GH) and prolactins (tPRL₁₇₇ and tPRL₁₈₈) in the tilapia (Oreochromis mossambicus). We observed no discernible patterns in serum GH that would suggest an effect of salinity, diet or MT. However, serum GH levels in all treatments declined at 1 and 3h after first feeding. Serum tPRL₁₇₇ and tPRL₁₈₈ were significantly higher in freshwater (FW) than in seawater (SW) and levels were significantly affected by dietary protein. tPRL₁₇₇ levels were higher in all groups fed a 35% protein diet, but tPRL₁₈₈ levels were higher only in the groups fed the MT-treated 35% protein diet; only serum tPRL₁₈₈ levels were affected by MT. Moreover, serum tPRL₁₇₇ and tPRL₁₈₈ increased throughout the sampling time-course. Subsequent work using fasted tilapia suggests that first feeding is likely to initiate the post-prandial suppression of serum GH levels. In contrast with the picture observed in blood, pituitary glands of SW animals showed higher levels of GH than FW fish. Pituitary GH was elevated by MT in both FW and SW. We also observed that pituitary tPRL₁₇₇ and tPRL₁₈₈ levels were higher in FW fish than in SW fish; tPRL₁₇₇ and tPRL₁₈₈ levels were elevated by MT only in FW animals. To assess the somatomedin activity of plasma from FW- and SW-reared tilapia, we measured [35S]-sulfate incorporation into ceratobranchial cartilage explants in vitro. Plasma from SW-adapted tilapia showed greater activity in this assay than plasma from FW-reared tilapia, suggesting that the GH-dependent IGF bioactivity of plasma is higher in SW-reared tilapia. Collectively, these studies suggest that the growth-promoting actions of SW rearing and of MT administration in tilapia may be linked to elevations in GH and/or prolactin (tPRL₁₇₇ and tPRL₁₈₈)levels.     

Effects of Dietary β-Hydroxy-β-Methylbutyrate on Growth and Survival of Nile Tilapia,Oreochromis niloticus,Vaccinated Against Streptococcus iniae

Abstract

β-hydroxy-b-methylbutyrate (HMB), a leucine catabolite, has been shown to cause increased disease resistance and growth in animal production. A vaccine produced from formalin killed bacteria and concentrated extracellular products of the ARS-98-60 Streptococcus iniae isolate has been used for the prevention of streptococcal disease in Nile tilapia, Oreochromis niloticus. In the present study, the effects of feeding HMB were determined in tilapia vaccinated by intraperitoneal (IP) injection of the S. iniaevaccine or unvaccinated (controls). Nile tilapia were fed diets containing either 0, 12.5, 25, or 50 mg HMB/kg diet for 14 days. The mean daily growth rate and feed efficiency showed no significant (P> 0.05) differences between the treatment groups. Dietary HMB supplementation did not enhance antibody production in unvacci-nated Nile tilapia following challenge. Dietary HMB supplementation did not enhance the survival of vaccinated Nile tilapia following challenge injection with 1 X10⁸ CFU of S. iniae.