Selective breeding for the hybrid striped bass (Morone chrysops, Rafinesque ×M. saxatilis, Walbaum) industry: status and perspectives

The hybrid striped bass (HSB) farming industry has considerable potential for growth into domestic retail markets, but expansion of this industry is limited by high production costs that dictate high prices for HSB. It is widely recognized within the industry that selective breeding of an improved HSB will be required to increase production efficiency and reduce market prices. A National Program of Genetic Improvement and Selective Breeding for the HSB Industry has been initiated and some progress has been made toward domestication of the parent species of the hybrid. However, uncertainty remains as to which breeding procedures will most rapidly yield sustainable genetic gains in key production traits. This paper consolidates and reviews general information on the biology of temperate basses (genus Morone) relevant to selective breeding of improved HSB. The topics covered include control of reproduction, geographic distribution of stocks and population genetic variation. This is followed by a brief review of the current application of selective breeding techniques, including those based on molecular markers. Finally, we discuss potential avenues for genetic improvement of HSB in a selective breeding program.     

Dietary vitamin E requirement of hybrid striped bass (Morone chrysops female × M. saxatilis male)

This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg⁻¹ from Na₂SeO₃ and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg⁻¹ as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg⁻¹ dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg⁻¹ had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg⁻¹. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg⁻¹ dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.     

Non-destructive measurement of sunshine bass, Morone chrysops (Rafinesque) ×Morone saxatilis (Walbaum), body composition using electrical conductivity

Abstract. We describe a rapid, non-destructive method for determining lean body mass (LBM; i.e. total body mass — total lipid mass) and lipid content in live fish. This method provides non-invasive determination of body composition by measuring the total body electrical conductivity (TOBEC) of an animal placed within a low-frequency electromagnetic field. This principle is governed by the different electrical properties of body fat and fat-free tissues. Relationships between TOBEC analysis and body composition were examined using juvenile sunshine bass (hybrid striped bass, Morone chrysops (Rafinesque) ♀× M. saxatilis (Walbaum) ♂) in a size range of 24–124g. Whole-body conductivity was significantly correlated to LBM, lipid, protein, water, and ash content. Analyses of an independent group of fish indicated TOBEC to be a reliable indicator of body composition. This method should prove useful for deriving body composition data at various phases of an experiment or a life cycle, rather than a single point in time as with destructive methods.     

Tank culture of larval sunshine bass, Morone chrysops (Rafinesque)×M. saxatilis (Walbaum), at three feeding levels

Sunshine bass, a hybrid of female white bass Morone chrysops (Rafinesque) and male striped bass M. saxatilis (Walbaum), fingerling production occurs almost exclusively in ponds. To increase production and maintain year‐round production in temperate climates, indoor tank culture is required. While tank production of fingerlings has been demonstrated, little is known about feeding requirements. Sunshine bass larvae, stocked at 75 L^?1 in 100 L of brackish water, were fed sequentially with rotifers Brachionus plicatilis cultured with a Nannochloropis algae paste and enriched with highly unsaturated fatty acids, decapsulated Artemia nauplii, and a microencapsulated commercial diet. The larvae in one treatment (three replicates) were initially fed rotifers at a daily rate of 20 mL^?1, then nauplii at an initial rate of 2 mL^?1, and then the commercial diet at 1 g. Larvae in two other treatments received two and three times as much food daily. The highest feeding rate resulted in a survival (52.9%) that was significantly higher than the survival rate (22.4%) of larvae fed the least. The total biomass produced was the highest in the treatment receiving the most food. The lowest feeding rate produced the least fish, but they were the heaviest. The intermediate feeding rate produced the shortest fish (11.3 mm).     

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.     

Survival of juvenile striped bass (Morone saxatilis) and Morone hybrid bass (Morone chrysops × Morone saxatilis) increased by addition of calcium to soft water

CaCl₂ was used to increase the total hardness of water in three ponds from 20 to 45–100 mg/l as CaCO₃ 5 days before harvest. CaCl₂ was also used to increase hardness from 10 to 70–200 mg/l as CaCO₃ in water used for holding and transporting fish after they were harvested from ponds. All groups of fish in water containing additional calcium had 80–99% survival compared with 16% survival for a group of fish without additional calcium in the water before or after harvest. Addition of 1% NaCl to the water did not increase survival.     

Differentiation of striped bass, Morone saxatilis (Walbaum), from a hybrid: effectiveness of training

Abstract The ability of consumers and fishermen to distinguish-between wild striped bass, Morone saxatilis (Walbaum), and its hybrids may be important to marketing farm-raised fish and managing wild stocks. The ability of randomly selected persons to distinguish between wild and hybrid specimens was examined and it was found that a significant improvement in recognition occurred with only minimal training. Average correct response of 70% without training rose to nearly 90% after training. Moreover, the respondents' sex and age were important factors in determining successful identification.     

Dietary cholesterol and lecithin have limited effects on growth and body composition of hybrid striped bass (Morone chrysops × M. saxatilis)

The effects of cholesterol and lecithin on growth and body composition of juvenile hybrid striped bass ( Morone chrysops  ×  M. saxatilis ) were investigated by feeding juvenile hybrids (initial weight 5.0 g) diets containing cholesterol at either 0 or 1% and lecithin at either 0, 2, 4, or 6% in a 2 × 4 factorial design. Each of the eight diets was fed to fish in triplicate 38-L aquaria maintained as a brackish water recirculating system for 8 weeks. Weight gain, feed efficiency, muscle ratio and hepatosomatic index were not significantly ( P  > 0.05) affected by dietary supplementation of cholesterol or lecithin. Supplementation of the diet with lecithin at 4 and 6% significantly ( P  < 0.05) decreased intraperitoneal fat accumulation regardless of dietary cholesterol level. Neither muscle nor liver lipid levels were significantly altered by dietary supplementation of cholesterol or lecithin although both liver and plasma lipid classes were affected. Dietary cholesterol decreased concentrations of liver and plasma free fatty acids and liver phospholipids while increasing concentrations of liver triglycerides and plasma phospholipids. Dietary lecithin did not consistently affect plasma and liver lipid classes although changes in phospholipid levels approaching significance ( P =0.0502 and P =0.0513, respectively) were observed. Thus it is concluded that dietary supplementation with cholesterol or lecithin had no substantial beneficial effects on growth or body composition of juvenile hybrid striped bass.     

Selenium nutrition of hybrid striped bass (Morone chrysops × M. saxatilis) bioavailability, toxicity and interaction with vitamin E

Two concurrent 12-week feeding trials were conducted to evaluate the bioavailability of inorganic sodium selenite and organic seleno-DL-methionine and to investigate the potential interaction between selenium and vitamin E in juvenile hybrid striped bass. In experiment 1, purified diets utilizing casein, gelatin and an amino acid premix as protein sources with a basal selenium concentration of 0.11 mg Se   kg⁻¹ were supplemented with either Na₂SeO₃ to provide selenium concentrations of 1.19, 2.00, 5.17 and 21.23 mg Se kg⁻¹ or with seleno-DL-methionine to provide 0.90, 1.26 and 2.55 mg Se kg⁻¹ and fed to juvenile hybrid striped bass in aquaria. A second experiment evaluated potential interactions by feeding these purified diets with or without supplemental vitamin E or sodium selenite, singularly or in combination. No overt selenium deficiency signs were exhibited by fish in either of the experiments; however, signs of selenium toxicity including retarded weight gain (WG), reduced feed intake and feed efficiency ratio (FER) as well as increased mortality, were observed in fish fed the diet containing more than 20 mg Se kg⁻¹. Whole-body selenium and whole-body selenium retention were linearly influenced by sodium selenite and selenomethionine. However, there was no significant effect of dietary selenium, vitamin E or their interaction on WG, FER and survival. Slope-ratio analysis showed that bioavailability of seleno-DL-methionine as a selenium source for juvenile hybrid striped bass was significantly ( P  < 0.01) higher (3.3-fold) than sodium selenite.     

Chemiluminescent responses of striped bass, Morone saxatilis (Walbaum), phagocytes to strains of Yersinia ruckeri

Abstract. Seventeen strains of Yersinia ruckeri were examined for plasmid DNA by means of agarose gel electrophoresis of partially cleared lysates. All 10 serotype I strains examined contained a 70 Megadalton (Mdal) plasmid, whereas only one of the 7 serotype II strains examined contained a plasmid of about 2–3 Mdal. Yersinia ruckeri exhibited distinctive colonial morphology and serological reactivities which suggested a possible correlation with plasmid content. The luminol-enhanced Chemiluminescent (CL) responses of striped bass, Morone saxatilis (Walbaum), phagocytes to different strains of Y. ruckeri were also studied. Some variability was observed; however, the greatest phagocyte CL responses were elicited by serotype II strains without the plasmid while serotype I strains harbouring the plasmid consistently elicited weak CL responses from phagocytes.     

Amino acid availability from animal, blended, and plant feedstuffs for hybrid striped bass (Morone chrysops × M. saxatilis)

The refinement of hybrid striped bass feed formulations has been progressing rapidly. There is still, however, limited information available regarding nutrient digestibility and amino acid availability from common feedstuffs. A pair of experiments was conducted to determine the protein digestibility and amino acid availability to sunshine bass from an assortment of commercially available animal protein feedstuffs, blended animal products and plant protein feedstuffs in extruded diets. The feedstuffs tested were blood meal, poultry by‐product meal, fish solubles, Pro‐Pak 60, Pro‐Pak 65, ProCon 65RDB, and 60FMC for the animal protein feedstuffs and brewer's yeast, canola meal, peanut meal, and sunflower meal for the plant protein feedstuffs. Test diets consisted of a mixture of nutritionally complete reference diet and test ingredient. Triplicate tanks of fish were fed their respective diets for 7 days prior to collection of faeces by stripping. Apparent digestibility coefficients of protein (ADC‐CP) in the animal products ranged from 47% for 60FMC to a high of 70% for fish solubles. ADC‐CPs for animal products were not different across products. Blood meal, poultry by‐product meal, Pro‐Pak 60, Pro‐Pak 65, and ProCon had intermediate ADC‐CPs of 63, 55, 63, 57 and 52%, respectively. ADC‐CP in plant feedstuffs ranged from 43% for canola meal to 80% for peanut meal. Brewer's yeast, canola meal, and sunflower meal had intermediate ADC‐CPs at 54, 43 and 69%, respectively. Apparent amino acid availability coefficients were variable across animal products and did not necessarily correlate to the ADC‐CPs for a given feedstuff. Isoleucine availability was low in blood meal at 38% compared with 59% or better for the remaining amino acids. Lysine, tyrosine and phenylalanine availability from fish solubles was low at 31, 35 and 44%, respectively. Amino acid availability from Pro‐Pak 60 was consistently higher across all amino acids for the animal products and blends tested. Of the plant products tested, peanut meal was the best performing feedstuff relative to amino acid availability.     

杂交条纹鲈苗种培育及成鱼养殖技术

杂交条纹鲈目前有两种 ,一种为六十年代中期在美国南加州生产的“原始杂交”种即用条纹狼鲈的卵与金眼狼鲈的精子人工杂交而得 ,另一种为雌性的金眼狼鲈与雄性的条纹狼鲈杂交种“阳光鲈”。条纹鲈和杂交条纹鲈为目前美国的主要养殖鱼类之一 ,主要用于游钓业及餐饮业。杂交条纹鲈因其具有显著的杂交优势 :生长速度快、个体大、抗病力强并具有集群摄食习性 ,易驯化饲养、起捕率高 ,且肉质白嫩、无肌间刺、营养价值高等特点 ,目前己成为淡水养殖的优良品种。我国台湾、沿海省份及内陆地区都已相继引进了杂交条纹鲈。根据我省近年来养殖该鱼的经…     

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.     

Reproduction of striped bass, Morone saxatilis (Walbaum), broodstock: monitoring maturation and hormonal induction of spawning

Abstract Levels of gonadal steroid hormones were quantified in an adult striped bass, Morone saxatilis (Walbaum), broodstock during their gametogenic cycle. Blood plasma concentrations of Estradiol (E₂) and testosterone in females, or 11-ketotestosterone(11-KT) and testosterone (T) in males, were used as indicators of maturation. In both sexes, hormone levels were low in summer but increased significantly by late October to intermediate levels which were then maintained until late January. They then increased again rapidly to maximum pre-spawning values attained in late February or March, and subsequently decreased during the spawning period (April and May) with an increased incidence of spent fish with low hormone levels. The changes in blood hormone concentrations coincided with annual changes in photoperiod and water temperature that may be useful landmarks for maturation in captive broodstock. Mature females were implanted with pellets containing a dose of approximately 20 μg/kg body weight of [D-Ala⁶-Pro⁹-Net]-LHRH (GnRHa) in a matrix of cholesterol (CH) and cellulose. In April, they had not yet begun final oocyte maturation (FOM) and were too immature for conventional induction of spawning by injection with human chorionic gonadotropin (hCG). In early April, females given two 95% CH (slow hormone-release) GnRHa pellets (95/95) or females given one 80% CH (fast hormone-release) GnRHa pellet and one 95% CH GnRHa pellet (80/95) spawned within 13 days treatment (n= 4) with good egg fertility (76 ± 7% of total) and hatch rates (62 ± 15% of fertile). Females given dual fast-release GnRHa pellets (80/80) or control (Sham) pellets did not spawn or show evidence of increased oocyte diameter or development. In late April, four of six females given the 80/95 GnRHa pellet combination spawned within 9 days. Three fish produced fertile eggs (54 ± 18%). one spawned overripe eggs, and the remaining two increased oocyte diameter and maturation. Three corresponding controls did not spawn, and two of these showed clear signs of atresia within 11 days. In early May, some females were undergoing early FOM and were mature enough to be spawned by hCG injection. Three were given a single 80% CH GnRHa pellet and spawned within 6 days of treatment to produce fertile eggs (44 ± 6%). Of two other females given dual 80% CH GnRHa pellets, one spawned infertile eggs and the other failed to spawn within 9 days. GnRHa implants show promise as a technique for inducing spawning of captive striped bass broodstock although the optimum hormone delivery systems, dosages and release rates should be verified for fish at specific maturational stages.     

Dietary threonine requirement of juvenile hybrid striped bass (Morone chrysops♀×M. saxatilis♂)

Two growth studies were conducted to determine the dietary threonine requirement of reciprocal cross hybrid striped (sunshine) bass. Semipurified diets were prepared with crystalline amino acids and lyophilized fish muscle to supply 350 g crude protein kg⁻¹ diet. The basal diet contained 4.9 g threonine kg⁻¹ from fish muscle, and test diets were supplemented with graded levels of L-threonine. In the first experiment, fish initially averaging ≊ 9.8 g each were fed diets containing threonine levels of 4.9, 7.5, 10.0, 12.5, 15.0 and 17.5 g kg⁻¹ dry diet for 7 weeks. Weight gain, feed efficiency and protein efficiency ratio (PER) were significantly ( P < 0.01) influenced by dietary threonine level. Based on weight-gain responses, a threonine requirement (± SE) of 8.4 (± 0.8) g kg⁻¹ dry diet was determined, and dietary threonine levels of 10.0 g kg⁻¹ diet or greater resulted in the highest levels of free threonine in plasma.
Based on the results of the first experiment, a second feeding trial was conducted with diets containing threonine levels of 4.9, 6.5, 8.0, 9.5, 11.0 and 12.5 g kg⁻¹ dry diet. Fish initially averaging ≊ 3.0 g each were fed each diet for 8 weeks. Weight gain, feed efficiency and PER values of fish were markedly improved, with increases in dietary threonine up to 8.0 g kg⁻¹ dry diet. Regression analysis of weight gain, feed efficiency and PER data using the broken-line model resulted in threonine requirement estimates of 9.7, 8.5 and 8.6 g kg⁻¹ dry diet, respectively. Based on these data, the threonine requirement of juvenile sunshine bass was determined to be ≊ 9.0 g kg⁻¹ dry diet or 26 g kg⁻¹ of dietary protein.     

Therapeutic and prophylactic immunization against Streptococcus iniae infection in hybrid striped bass (Morone chrysops×Morone saxatilis)

Vaccination strategies have traditionally been used as preventative or prophylactic measures against disease (prophylactic immunization) in uninfected fish. Alternatively, therapeutic or remedial measures, such as antibiotic administration, are commonly employed to treat disease in infected fish. Vaccination as a therapeutic measure (therapeutic immunization), however, has not been adequately explored in sub‐clinically infected fish. Therapeutic and prophylactic immunization with three Streptococcus iniae vaccines, formalin‐killed whole S. iniae cells (FKC vaccine), concentrated S. iniae extracellular products (greater than 2 kDa) (ECP vaccine) and a combination of killed cells and extracellular products (FKC+ECP vaccine), were tested in hybrid striped bass, Morone chrysops×Morone saxatilis, previously naturally infected with S. iniae. Fish (mean weight 10.0 g) were injected intraperitoneally (IP) or intramuscularly (IM) with one of each of the vaccines, tryptic soy broth (TSB‐control) or non‐injected (non‐injected control) to evaluate therapeutic effects (Trial 1). Survivors of the natural infection and ECP and FKC+ECP vaccine immunization and another lot of non‐injected control fish were immersion challenged with 1.47 × 10⁶ CFU of S. iniae mL^?1 at 44 days post‐immunization to evaluate vaccine efficacy (Trial 2). Hybrid striped bass (1.0 g) were also IM injected with S. iniae ECP vaccine at an aquaculture facility and immersion challenged with 1.47 × 10⁶ CFU of S. iniae mL^?1 12 weeks post‐immunization (Trial 3). The ECP and FKC+ECP vaccines, regardless of injection route, significantly (P<0.001) increased survival in asymptomatic, sub‐clinically infected fish thereby providing therapeutic merit. Hybrid bass immunized IP or IM had mean per cent survival values ranging from 78 to 96 at 44 days post‐immunization (Trial 1) and 69–97 post challenge (Trial 2). Survival of fish injected with TSB or immunized with FKC vaccine was significantly lowered and ranged from 12 to 13 by IP injection and 40 to 50 by IM injection and thus, the FKC vaccine had no therapeutic effect. The survival of hybrid striped bass IM immunized with S. iniae ECP vaccine in field Trial 3 was 91 and the RPS was 83. These results demonstrate that therapeutic immunization using S. iniae ECP and FKC+ECP vaccines can control a natural S. iniae infection. Furthermore, S. iniae ECP or FKC+ECP vaccines can also be used prophylacticly to protect hybrid striped bass against subsequent pathogen challenge.