Development of an ELISA to measure the humoral immune response of hybrid striped bass Morone chrysops×M. saxatilis to Streptococcus iniae

A previously developed monoclonal antibody (mAb) specific for the heavy chain of hybrid striped bass (HSB) Morone chrysops×M. saxatilis immunoglobulin was used in an assay to detect the humoral response to antigens of Streptococcus iniae. In order to validate this assay, an anti‐S. iniae antibody was produced in HSB by immunization with formalin‐killed cells of S. iniae mixed with Freund's complete adjuvant (FCA). After boosting with cells mixed with Freund's incomplete adjuvant (FIA), fish were challenged with live S. iniae by i.p. injection. This resulted in mortalities of 100%, 13% and 7% for non‐immunized, immunized and non‐challenged fish respectively. Live S. iniae were recovered only from moribund non‐immunized challenged fish, indicating that the immunization conferred protection against S. iniae. Sera were taken at 28 and 42 days post challenge and anti‐S. iniae antibody was measured by both agglutination and indirect ELISA. Titres of anti‐S. iniae antibody increased only in the immunized group as measured by agglutination and ELISA. Serum complement measured in the final bleeding was significantly higher in the immunized group. Western blotting using immune HSB serum indicated that the predominant antigen in this case was the high molecular weight polysaccharide of S. iniae.     

Comparison of Purified and Practical Diets Supplemented with or without β-Glucan and Selenium on Resistance of Hybrid Striped Bass Morone chrysops ♀× M. saxatilis ♂ to Streptococcus iniae Infection

This study was conducted to evaluate the efficacy of β-glucan and selenium supplements to the diet on increasing survival of hybrid striped bass Morone chrysops X M. saxatilis exposed to Streptococcus iniae. A 2 × 2 × 2 factorial design was employed by including purified casein/gelatin-based diets and practical menhaden fish meal-based diets with supplement! of either β-glucan from barley at 0 and 0.1 % of diet or sodium selenite at 0 or 0.2 mg/kg diet or a combination of these supplements. All diets were formulated to meet the nutritional needs of hybrid striped bass with the exception of selenium. The purified and practical basal diets contained 0.03 and 1.03 mg Se/kg, respectively, and the diets supplemented with sodium selenite had an additional 0.07 mg Se/kg on average. Juvenile hybrid striped bass initially averaging 2.44 ± 0.17 g/fish were fed the eight experimental diets in triplicate 110-L recirculating aquaria for 6 wk, after which they were immersed in a bath of S. iniae at 6.2 × 10⁶ CFU/mL for 2 h and monitored for 21 d. Weighi gain and feed efficiency were significantly (P < 0.05) affected by diet type and selenium supplementation, with fish fed practical diets and those supplemented with selenium having the greatest values. Supplementation of β-glucan to the purified or practical type diets did not significantly affect survival of fish after experimental infection. The most notable difference (P < 0.0001) was in the comparison of diet type; the survival rate of fish fed the practical diets was 75% compared to 35% for those fed the purified diets. Dietary supplementation of β-glucan did not enhance disease resistance in the present study. Fish fed menhaden fish meal-based diets were significantly more resistant to 5. iniae in comparison to the those fed the purified diets. Thus, nutritional influences on disease resistance of hybrid striped bass were evident in this study and warrant further investigation.     

Commercial Diets in Phase I Palmetto Bass,Morone saxatilis × Morone chrysops,Production in Plastic‐lined Ponds: Fertilizer or Feed?

The role of offering a commercial pelleted diet has been characterized as both an expensive organic fertilizer and as a selected food item for larval hybrid striped bass (palmetto), Morone saxatilis × Morone chrysops, culture operations. In this study, we examined the effects of providing a commercial diet on fish production and zooplankton dynamics during phase I culture in plastic‐lined ponds. We also sought to estimate relative dietary contribution of a commercial fish feed relative to natural pond biota using stable isotope tissue analysis. Palmetto bass were stocked into six 0.04‐ha plastic‐lined ponds at a rate of 125,000/ha. During the 31‐d culture period, ponds were fertilized with alfalfa pellets at a rate of 112 kg/ha/wk. At 14 d post‐stock (dps), Silver Cup Trout Fry diet was offered at a rate of 13.6 kg/ha/d and fertilization was discontinued in three ponds. Although mean final fish length was significantly greater within the fed treatment, no other production parameters were found to be different (P < 0.1). Following feed application, copepod concentrations within the fed ponds were greater in magnitude by 24 dps. Through stable isotope tissue analysis, we found a significant enrichment in both ¹³C and ¹⁵ν of fish, zooplankton, and Chironomidae larvae within the fed ponds (P < 0.10). Using a three‐source mixing model, the mean (±SE) percent composition of feed in the fish's isotopic signature increased from 5% ±2 to 20% ±6 within 16 d. Although fish production was not greatly affected through the addition of a commercial fish feed, enriched ¹³C and ¹⁵ν of fish tissue indicate that palmetto bass fingerlings increasingly utilized the prepared diets over time. However, based on the isotopic values of fish and potential food sources, it can be estimated that natural pond biota likely accounted for up to 80% of nutrient assimilation in the hybrid striped bass.     

Growth response and acquired resistance of Nile tilapia, Oreochromis niloticus (L.) that survived Streptococcus iniae infection

This study determined the growth performance and acquired resistance of Nile tilapia, Oreochromis niloticus (L.) that survived Streptococcus iniae infection. Tilapia were challenged with three doses of S. iniae (8.8 × 10³, 8.8 × 10⁴ and 8.8 × 10⁵ CFU fish^?1 for low, medium and high challenges respectively). Groups of non‐injected and tryptic soy broth‐injected fish were maintained as controls. Significantly (P<0.05) higher mortality (45.0%) occurred in the high challenge treatment than in the low challenge treatment group (29.6%). The medium challenge group had mortality (36.3%) that did not differ significantly from the high or low treatment. Few fish died in the non‐injected and broth‐injected treatments (3.4% and 0.8% respectively). The tilapia that survived S. iniae infection used to assess growth performance were selected from survivors without gross clinical signs of disease. These fish were randomly stocked at a rate of 30 fish into each 57 L aquarium in triplicate and fed to apparent satiation for 8 weeks. No significant differences were detected in weight gain, feed intake, feed efficiency ratio or survival between S. iniae‐survived tilapia and the control treatments following the 8‐week growth performance trial. Following the 8‐week feeding study, tilapia were challenged with 1 × 10⁶ CFU fish^?1 of S. iniae to assess acquired immunity. Mean cumulative mortality was significantly higher (P<0.05) in the control treatments (41.7% for the non‐injected and 43.3% for the broth‐injected fish) than in the low, medium and high challenge treatments (7.4%, 3.3% and 8.3% respectively). Serum protein was significantly (P<0.05) elevated in the S. iniae‐survived tilapia that were subsequently challenged when compared with controls challenged for the first time. Agglutinating antibody titre was significantly higher in the fish in the medium and high challenge treatments, compared with the control fish challenged for the first time. The results suggest tilapia that survive S. iniae challenge without showing overt disease signs performed as well as non‐infected tilapia. Further, the S. iniae‐survived tilapia challenged following the 8‐week growth performance trial gained acquired resistance to homologous S. iniae challenge.     

Retention mechanisms of white perch (Morone americana) and striped bass (Morone saxatilis) early-life stages in an estuarine turbidity maximum: an integrative fixed-location and mapping approach

The small‐scale distribution and retention mechanisms of white perch (Morone americana) and striped bass (M. saxatilis) early‐life stages were investigated in the upper Chesapeake Bay estuarine turbidity maximum (ETM). Physical measurements and biological collections were made at fixed‐location stations within the ETM during three research cruises in 1998 and two in 1999. Results were compared with mapping surveys of physical properties and organism distributions above, within, and below the ETM. Physical conditions at the fixed stations differed markedly among cruises and between years due to differences in freshwater flow and wind. In each year, striped bass and white perch larval concentrations were highest in waters of salinity 1–4. Larvae were more abundant in the ETM region in 1998, a high‐flow year, suggesting that the ETM provides favorable nursery habitat when low salinity waters and the ETM coincide in high freshwater‐flow conditions. In 1998, the earliest pelagic life stages of fish larvae (eggs, yolk‐sac larvae) and the copepod Eurytemora affinis, an important prey of feeding larvae, apparently were retained in deep, landward‐flowing water within the salt front and ETM region. Statistical analyses indicated that distributions of white perch and striped bass post‐yolk‐sac larvae were associated with E. affinis distributions and suggested that retention of larval fish could result from tracking prey. Comparing fixed‐station and mapping approaches demonstrates the importance of sampling at different spatial scales within the ETM region and suggests that larvae are faced with trade‐offs between selecting zones of high retention or high visual‐feeding success.     

Comparative Oxygen Consumption and Metabolism of Striped Bass Morone saxatilis and its Hybrid M. chrysops♀ xM. saxatilis♂

It has been reported that metabolic rates of striped bass Morone saxatilis and hybrid striped bass M. chrysops♀ x M. saxatilis♂ are different. A series of experiments were conducted to further characterize oxygen consumption and metabolism of striped bass and its hybrid, the sunshine bass. Oxygen consumption was measured to determine standard and routine metabolic rates of striped bass and hybrid striped bass in a freshwater, flow‐through tank system. Additionally, blood chemistry stress indicators of the two bass groups were compared in both fresh and brackish water. Hematocrit (% PCV) and hemoglobin were measured in order to compare oxidative efficiencies of the bass. Plasma glucose, chlorides, and cortisol levels were measured to compare the relative stress status of the two bass types reared under experimental conditions. No significant differences were found in average daily oxygen consumption between striped bass and sunshine bass for either standard metabolism (P= 0.92), or routine metabolism (P = 0.86). Standard metabolic rates of oxygen consumption were 69 ± 4.1 and 68 ± 3.5 mg 0₂/kg³/⁴ bw/h for sunshine bass and striped bass respectively. Routine metabolic rates were 132 ± 30 and 125 ± 30 mg O₂/kg^3/4 bw/h for sunshine bass and striped bass respectively. While there were no significant differences in oxygen consumption between species, normal feeding activity generally resulted in increased oxygen consumption by the fish. Striped bass had significantly lower hematocrit values (P= 0.0001), but significantly higher hemoglobin concentrations than sunshine bass maintained in freshwater (P= 0.0001). Striped bass had significantly higher (P= 0.0001) levels of plasma glucose compared to sunshine bass (176 ± 8.6 vs. 103 ± 5.6 mg/dL respectively). Plasma chloride levels for striped bass (123 ± 1.9 mEq/L) were significantly higher (P= 0.041) than plasma chloride levels of sunshine bass (117 ± 1.7 mEq/L). Plasma cortisol levels were significantly higher (P= 0.0081) for striped bass (147 ± 8.4 ng/mL) compared to sunshine bass (119 ± 5.6 ng/ mL) when reared in freshwater. When maintained in brackish water, sunshine bass had significantly higher hematocrit values (P= 0.0001), and hemoglobin concentrations (P= 0.0012) when compared to striped bass. However, sunshine bass had significantly higher hemoglobin concentrations (P= 0.0012) when compared to striped bass. In addition, plasma glucose levels were significantly lower (P = 0.0079) for sunshine bass (79 ± 4.1 g/dL) when compared to striped bass (115 ± 11 g/dL). There were no significant differences between the bass in levels of chlorides or cortisol. No differences were detected in oxygen consumption. However, hybrid striped bass may have more efficient oxidative metabolism due to elevated hemoglobin concentrations. While striped bass hemoglobin values tended to be higher in brackish water than in freshwater, sunshine bass hematocrit or hemoglobin values generally were significantly higher than striped bass in both fresh and brackish water. Based on these results, hybrid striped bass may be capable of directing more energy towards growth than striped bass due to more efficient oxidative metabolism and lower losses of energy related to increased stress.     

Evaluation of Growth Performance and Whole-body Composition of Juvenile Hybrid Striped Bass Morone chrysops × Morone saxatilis and Red Drum Sciaenops ocellatus Fed High-protein and High-lipid Diets

To investigate potential use of increasing nutritional density of diets for rapid growth of warm‐water fishes, a feeding trial was conducted in which growth performance, body indexes, and whole‐body composition of juvenile hybrid striped bass fed diets comprising protein (49, 54, and 59%), lipid (16, 20, 23, and 28%), and energy (22.0–25.1 kJ/g) concentrations beyond established minimum levels were compared to those of fish fed a more typical commercial reference diet (37.5% crude protein, 10.5% crude lipid, and 19.6 kJ/g energy on a dry matter basis). A subset of the experimental diets and the commercial reference diet also were fed to juvenile red drum. After 6 wk of feeding, hybrid striped bass fed the high‐protein and high‐lipid diets showed much greater growth performance compared to fish fed the commercial diet. Increasing dietary protein level, but not lipid level, tended (P ≤ 0.1) to enhance weight gain and feed efficiency of hybrid striped bass. Hepatosomatic index (HSI), intraperitoneal fat (IPF) ratio, and whole‐body protein were significantly (P < 0.01) influenced by dietary protein level. The dietary lipid and associated energy level had significant negative linear effects on daily feed intake. Linear regression analysis showed that dietary energy : protein ratio, largely influenced by dietary protein level, moderately but significantly influenced weight gain, HSI, IPF ratio, and whole‐body protein of hybrid striped bass and red drum. Red drum grew very similar to hybrid striped bass in response to the experimental diets. However, significant differences in HSI, IPF ratio, whole‐body protein, lipid, moisture, and ash between hybrid striped bass and red drum were observed, indicating species differences in protein and energy partitioning. In particular, the excessive lipid in the diet increased HSI and whole‐body lipid of red drum but not of hybrid striped bass.     

Quantitative dietary lysine requirement of juvenile striped bass Morone saxatilis

Two feeding trials of 8 and 10 weeks each were conducted to quantify the dietary lysine requirement of juvenile striped bass, Morone saxatilis. Diets in both experiments contained approximately 420 g crude protein kg^–1 and 13.4 MJ digestible energy (DE) kg^?1. L ‐Lysine‐HCl was added to the basal diet to yield five and six treatments in the two experiments. Diets in the first experiment were determined to contain 9.2, 14.1, 14.6, 19.9 and 21.0 g available lysine kg^?1 on a dry‐matter basis. Diets in the second experiment were determined to contain 14.8, 18.1, 21.3, 24.5, 27.6 and 30.9 g available lysine kg^?1 on a dry‐matter basis. Weight gain, specific growth rate (SGR), feed conversion ratio (FCR), and apparent nitrogen utilization (ANU) were significantly (P < 0.05) improved by increasing dietary lysine concentrations to approximately 20 g kg^?1 of diet. Least‐squares regression analysis of weight gain and SGR in the first experiment indicated a minimum dietary lysine requirement of 20.1 ± 2 g kg^?1 dry diet. Least‐squares regression analysis of the same criteria measured in the second experiment yielded the following estimates of dietary lysine requirements (g kg^?1 dry diet): 19.8 ± 2.3 for weight gain, 21.7 ± 1.5 for SGR, 23.7 ± 3.5 for FCR and 18.6 ± 1.3 for ANU. From these results the minimum recommended dietary lysine requirement for optimal growth of juvenile striped bass is approximately 21 g kg^?1 dry diet which equates to 49 g kg^?1 dietary protein or 1.57 mg kJ^?1 DE. Although higher than that reported for hybrid striped bass, this requirement level is similar to those reported for many other fish species.     

Hepatic glucose utilization and lipogenesis of hybrid striped bass (Morone chrysops × Morone saxatilis) in response to dietary carbohydrate level and complexity

The influence of carbohydrate level and complexity on in vitro hepatic glucose utilization and lipogenesis were determined in hybrid striped bass, Morone chrysops ♀ × Morone saxatilis ♂. Six isocaloric, isonitrogenous diets containing glucose, maltose, or dextrin at two different levels (200 or 400 g kg^?1 diet) were fed to adult fish for 15 weeks. Liver explants were obtained at near‐maximum postprandial glycaemic response and incubated with radioactive labelled substrates. Glycogen synthesis from [¹⁴C]glucose was not different among treatments and was less than ¹⁴CO₂ formation. ¹⁴CO₂ production increased as a function of carbohydrate level but was unrelated to carbohydrate complexity. There was no detectable conversion of [¹⁴C]glucose to lactate for any treatment. Rates of de novo lipogenesis from [1‐¹⁴C]acetate were high in comparison to [U‐¹⁴C]glucose or [9,10‐³H]palmitate incorporation into liver lipids and differed in response to carbohydrate level and complexity. [9,10‐³H]palmitate esterification was an order of magnitude less than glycogen and CO₂ production but 4–10 times greater than [¹⁴C]glucose incorporation into liver lipids. Palmitate incorporation did not differ among treatments. Incorporation of [¹⁴C]glucose into liver lipids was higher in fish fed diets containing 400 g kg^?1 carbohydrate. These data support the idea that glucose is not a major oxidative substrate in hybrid striped bass and indicate that the level of soluble carbohydrate should be limited to 200 g kg^?1 diet or less for hybrid striped bass.     

Spatial and temporal patterns in the distribution and feeding habits of Morone saxatilis in marsh creeks of Delaware Bay, USA

Delaware River and Bay Morone saxatilis (Walbaum), striped bass, have recently undergone a dramatic recovery. Here, we examine spatio‐temporal patterns in the distribution and food habits of striped bass in marsh creeks in the estuary (salinity range 1–20 psu), 1996–2000. Sampling occurred monthly, April through November, with otter trawls (4.9 m, 6 mm mesh, n = 6760) and weirs (intertidal block nets, 6 mm mesh, n = 647) at eight sites. Young‐of‐the‐year (YOY) fish were generally more than 10 times more abundant at oligohaline sites, although they were abundant at mesohaline sites in 1996, the lowest salinity year. Small striped bass (<100 mm) in creeks relied on mysids and other crustaceans and became more piscivorous with size. Overall, they consumed 46% by weight fish, of which 52% were mummichog, Fundulus heteroclitus (L.), and 18% were YOY Atlantic croaker, Micropogonias undulatus (L.), prey types which are not typical in most food habits studies and are indicative of feeding in marsh creeks. These data suggest that young striped bass are an abundant component of Delaware Bay marsh creek fauna and may play an important role in trophic relays within this system.     

Experimental Infection of Rainbow Trout,Oncorhynchus mykiss,and Hybrid Striped Bass,Morone chrysops ♂ × Morone saxatilis ♀, with Viral Hemorrhagic Septicemia Virus Genotype IVb

The emergence of a new sublineage of viral hemorrhagic septicemia virus (VHSV) within the Laurentian Great Lakes has caused concern for aquaculture in the United States. Because of the occurrence of VHSV in a new geographic location, new host species have been identified and the complete host range has not been determined. This study confirmed the high resistance of rainbow trout, Oncorhynchus mykiss, to VHSV type IVb infection. In addition, the experimental susceptibility of hybrid striped bass, Morone chrysops ♂ × Morone saxatilis ♀, to VHSV type IVb infection was examined but determined to be highly dependent on age of fish and exposure temperature. No mortality was observed in adult fish infected via intraperitoneal (IP) injection at 15 C, whereas yearling fish infected via IP injection under the same conditions experienced 20.8% mortality. Among yearling fish infected via IP injection, mortality increased to 100% when exposure to VHSV occurred at 10 C. An LD₅₀ for yearling hybrid striped bass exposed to VHSV at 10 C by IP injection was determined to be 1.4 × 10⁴ pfu (SE = 2.1). Thus, at 10 C, yearling hybrid striped bass experience a high mortality when exposed to VHSV IVb by IP injection.     

Resistance to Streptococcus iniae and its genetic associations with traits of economic importance in Asian seabass (Lates calcarifer)

Streptococcus iniae is one of the most serious aquatic pathogens, causing significant economic losses in marine and freshwater species, including Asian seabass (Lates calcarifer). Controlling this gram‐positive bacterial pathogen has been an issue in aquaculture systems, due to the combined effects of aquaculture intensification and climatic impacts. To date, there have not been any genetic parameter estimates for S. iniae resistance in Asian seabass. The main aim of this study was to examine genetic variation in S. iniae resistance and its genetic correlations with growth and cannibalism in Asian seabass families produced from a breeding programme for high growth in 2016 and 2017. The study included a total of 5,835 individual fish that were offspring of 41 sires and 60 dams (31 half‐sib and 34 full‐sib families). The experimental fish were challenged by intraperitoneal injection with a volume containing 10⁵ CFU (colony‐forming unit)/fish. Resistance to S. iniae was measured as survival rate at 6 hr, 3, 5, 7, 10 and 15 days post‐challenge test. There were significant variations in S. iniae resistance among families at different observation periods (ranging from 24.4% to 80%). Restricted maximum‐likelihood method and mixed model analysis were applied to estimate heritability for S. iniae resistance. The heritability for S. iniae resistance ranged from 7% to 18% across different statistical models used. The common full‐sib effects accounted for 0.1%–2% of the total variation in resistance to S. iniae. Genetic correlations of the S. iniae resistance at 6 hr and 3 days with later post‐challenge test periods were low to moderate. However, these estimates for S. iniae resistance between successive measurement times (5, 7, 10 and 15 days) were high and close to 1. The genetic correlations of resistance with body weights at 180, 270 and 360 days post‐hatch were not significant as well with cannibalism. It is concluded that there is substantial additive genetic variation in resistance to S. iniae, suggesting there is potential for genetic improvement of Asian seabass for resistance to S. iniae through selective breeding.     

Effect of triiodothyronine on the growth and survival of larval striped bass (Morone saxatilis)

This study was carried out to test the effect of triiodothyronine (T₃) on the growth and survival of larval striped bass (Morone saxatilis). Growth and survival of striped bass held in 5 ppt seawater and treated with various doses of T₃ were measured beginning at 5 and 16 days after hatching. Body content of T₃ was measured by radioimmunoassay. T₃ dissolved in the 5 ppt seawater was taken up by larval striped bass in a dose-dependent manner, and affected the growth and survival of the fish. At 5 days after hatching, T₃ at 100 ng ml^–1 and 50 ng ml^–1 retarded the growth of larval striped bass and caused a lower survival rate than T₃ at 25 ng ml^–1 or the control treatment. At 16 days after hatching, T₃ at 100 ng ml^–1 retarded the growth of larval fish and caused a higher mortality. T₃ at 10 ng ml^–1 and 1 ng ml^–1 did not show any effect on either survival or growth. Body content of T₃ returns to control levels within days following end of treatment. The results indicate that exogenous T₃ can be detrimental to the growth and survival of larval striped bass.     

Genetic effects on carcass-quality traits in hybrid striped bass (Morone chrysops♀×Morone saxatilis♂)

A 10 × 10 factorial mating design was used to examine the genetic effects on various carcass‐quality traits in hybrid striped bass (Morone chrysops♀×Morone saxatilis♂). A total of 448 offspring were raised in a ‘common‐garden’ environment and carcass‐quality traits were assessed at 389 days post fertilization; parentage of each fish was inferred from genotypes at 5–10 nuclear‐encoded microsatellites. There was a significant effect of dam and sire on body weight and fillet weight and a significant effect of dam on viscera weight and condition factor. When carcass‐quality traits were standardized to body weight, there was a significant effect of dam, sire and dam × sire interaction on viscera percentage (proportion of viscera weight to body weight). Phenotypic correlations between body weight and non‐standardized carcass‐quality traits were high (r_p=0.80–0.92), whereas phenotypic correlations between body weight and standardized carcass‐quality traits were low (r_p=0.13–0.19). Genetic correlations between body weight and fillet weight (dams and sires), and body weight and viscera weight (dams only) were significant and positive, while the genetic correlations between body weight and viscera percentage (dams and sires) were significant and negative. Significant general combining ability values for favourable carcass‐quality traits in the same breeder (dam or sire) occurred only in one or two of 20 (dams and sires) used in this study, suggesting that simultaneous improvement in multiple traits in hybrid striped bass may require evaluation of large numbers of candidate breeders. The effect of sex on body weight and all non‐standardized carcass‐quality traits was significant and appeared to be due to faster growth in females. These results indicate that selection for faster growth of hybrid striped bass would lead to a correlated increase in fillet weight and viscera weight but not necessarily to an increase in the proportion of fillet and waste product generated. The significant dam, sire and dam × sire interaction effects on viscera percentage and the negative genetic correlations between body weight and viscera percentage indicate that selection for reduced proportion of viscera relative to body weight might be feasible.     

Whole cell inactivated autogenous vaccine effectively protects red Nile tilapia (Oreochromis niloticus) against francisellosis via intraperitoneal injection

Francisella noatunensis subsp. orientalis is a pathogen of tilapia and other warm‐water fish for which no vaccines are commercially available. In this study, a whole cell formalin‐inactivated vaccine was developed for the first time using the highly virulent isolate STIR‐GUS‐F2f7 and the oil‐based adjuvant Montanide? ISA 763A VG. The efficacy of the vaccine was assessed in red Nile tilapia via intraperitoneal (i.p.) injection using homologous experimental infection and correlates of protection such as seral antibody production and bacterial loads in the spleen. For immunization, fish were i.p. injected with 0.1 ml of the vaccine, the adjuvant alone or PBS. At 840 degree days post‐vaccination, all fish were i.p. injected with 4.0 × 10³ CFU/fish of pathogenic bacteria. The RPS at the end of the trial was 100% in the vaccinated group with significantly higher survival than in the adjuvant and control groups. The RPS in the adjuvant group was 42%, and no significant difference was seen in survival between this and the PBS group. Moreover, significantly higher antibody titres in the serum and significantly lower bacterial loads in the spleen were detected in the vaccinated fish by ELISA and qPCR, respectively. These findings highlight the potential of autogenous vaccines for controlling francisellosis in tilapia.     

Growth performance,blood biochemical parameters,immune response,and antioxidant defense of Asian seabass (Lates calcarifer) fingerlings exposed to monovalent and bivalent vaccines against Streptococcus iniae and Vibrio harveyi

The present study investigated the effects of monovalent and bivalent vaccines against Streptococcus iniae and Vibrio harveyi on growth performance, blood biochemical parameters, immune system, and antioxidant defense of Asian seabass (Lates calcarifer) fingerlings. Fish were exposed to seven experimental groups containing phosphate buffer saline (control), S. iniae vaccine by injection, S. iniae vaccine by immersion method, V. harveyi vaccine by injection, V. harveyi vaccine by immersion method, S. iniae/V. harveyi vaccines by immersion method, and S. iniae/V. harveyi vaccines by injection in triplicate for 60 days. Vaccination resulted in a significant alteration of the final weight (FW), feed conversion ratio (FCR), daily weight gain (DWG), relative growth rate (RGR), glucose, lysozyme, and complement levels at 60 days post-vaccination. Also, serum glutathione activity significantly increased in group SVIM (S. iniae/V. harveyi vaccines by immersion method) compared to the control group at 60 days post-vaccination. The level of MDA in serum was significantly decreased in SIN (S. iniae vaccine by injection) and SVIM groups compared to the control group 60 days post-vaccination where the value of this parameter was significantly higher in VIM (V. harveyi vaccine by immersion method) and SVIN (S. iniae/V. harveyi vaccines by injection) groups. The results of this study suggest that exposure to monovalent and bivalent vaccines against S. iniae and V. harveyi could alter the growth performance, nonspecific immune response, and antioxidant defense of Asian seabass fingerlings.

     

Development of attenuated erythromycin‐resistant Streptococcus agalactiae vaccine for tilapia (Oreochromis niloticus) culture

Streptococcus agalactiae is an important pathogen in fish, causing great losses of intensive tilapia farming. To develop a potential live attenuated vaccine, a re‐attenuated S. agalactiae (named TFJ‐ery) was developed from a natural low‐virulence S. agalactiae strain TFJ0901 through selection of resistance to erythromycin. The biological characteristics, virulence, stability and the immunization protective efficacy to tilapia of TFJ‐ery were determined. The results indicated that TFJ‐ery grew at a slower rate than TFJ0901. The capsule thickness of TFJ‐ery was significantly less (p < 0.05) than TFJ0901. When Nile tilapia were intraperitoneally (IP) injected with TFJ‐ery, the mortality of fish was decreased than that injected with TFJ0901. The RPS of fish immunized with TFJ‐ery at a dose of 5.0 × 10⁷ CFU was 95.00%, 93.02% and 100.00% at 4, 8 and 16 weeks post‐vaccination, respectively. ELISA results showed that the vaccinated fish produced significantly higher (p < 0.05) antibody titres compared to those of control at 2 or 4 weeks post‐vaccination. Taken together, our results suggest that erythromycin could be used to attenuate S. agalactiae, and TFJ‐ery is a potent attenuated vaccine candidate to protect tilapia against S. agalactiae infections.     

Dietary tryptophan requirement of hybrid striped bass (Morone chrysops × M. saxatilis)

Requirements for six of the 10 indispensable amino acids (IAA) have not been quantified for hybrid striped bass. In this study, we estimate the requirement for l ‐tryptophan by nonlinear regression analysis of several growth indicators. Fifteen isocaloric, isonitrogenous diets were formulated to contain 1.0, 1.3, 1.6, 1.9, 2.2, 2.5, 2.8, 3.1, 3.4, 3.7, 4.0, 5.0, 6.0, 10.0 or 14 g l ‐tryptophan kg^?1 diet and fed to reciprocal cross hybrid striped bass for 7 weeks. After 5 weeks, survival of fish receiving the basal diet was 40% while surviving fish fed this diet were in poor health. Survival of fish receiving 1.3 g Trp kg^?1 diet declined to 70% by termination of the trial. Survival in other treatments was 100%. Fish weight gain was 100% or greater for fish receiving 1.6 g Trp kg^?1 diet or more. Hepatosomatic index, muscle ratio and intraperitoneal fat (IPF) ratio also responded to dietary tryptophan concentration. IPF was inversely related to dietary tryptophan concentration. The dietary tryptophan requirement was estimated to be between 2.1 and 2.5 g kg^?1 diet (6–7 g kg^?1 protein), depending on response variable, using four‐ and five‐parameter saturation kinetics models. These findings will increase the precision of diets formulated for hybrid striped bass.     

Physiology of seawater acclimation in the striped bass,Morone saxatilis (Walbaum)

Several experiments were performed to investigate the physiology of seawater acclimation in the striped bass, Morone saxatilis. Transfer of fish from fresh water (FW) to seawater (SW; 31–32 ppt) induced only a minimal disturbance of osmotic homeostasis. Ambient salinity did not affect plasma thyroxine, but plasma cortisol remained elevated for 24h after SW transfer. Gill and opercular membrane chloride cell density and Na⁺,K⁺-ATPase activity were relatively high and unaffected by salinity. Average chloride cell size, however, was slightly increased (16%) in SW-acclimated fish. Gill succinate dehydrogenase activity was higher in SW-acclimated fish than in FW fish. Kidney Na⁺, K⁺-ATPase activity was slightly lower (16%) in SW fish than in FW fish. Posterior intestinal Na⁺,K⁺-ATPase activity and water transport capacity (J_v) did not change upon SW transfer, whereas middle intestinal Na⁺,K⁺-ATPase activity increased 35% after transfer and was correlated with an increase in J_v (110%). As salinity induced only minor changes in the osmoregulatory organs examined, it is proposed that the intrinsic euryhalinity of the striped bass may be related to a high degree of “preparedness” for hypoosmoregulation that is uncommon among teleosts studied to data.     

Early growth and survival of striped bass, Morone saxatilis (Walbaum), and its phenotypically similar hybrid (M. saxatilis × M. chrysops) using an otolith marking method

An experiment using differently marked larval striped bass, Morone saxatilis (Walbaum). and its hybrid (M. saxatilis x M. chrysops (Rafinesque)) was performed in two grow-out ponds. Larval striped bass were immersed in oxytetracycline solution to mark their otoliths; hybrids received no treatment. Larvae from both groups were mixed and stocked at 8 days post hatch into the ponds. Striped bass and hybrid larvae grew to a significantly larger size at 35 days in one pond. In both ponds, hybrid lengths at 35 days after hatch were significantly greater than striped bass lengths. However, the magnitude of the size difference between hybrids and striped bass was twofold greater (10%) in one pond than in the other (5%). The proportion of striped bass juveniles at 35 days differed from the initial stocking proportion (0.53) only in one pond, where hybrids showed 12% greater survival than striped bass. Results suggested that the relative survival of hybrids was influenced by growth conditions in the ponds. Based on the ease of protocol and analysis of the marking experiment, we recommend its use to (1) investigate relative performance between genetic groups of young fish in common environments; and (2) predict the effects of introductions of genetically altered fishes.