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.     

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.     

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.     

The effect of exogenously administered recombinant bovine somatotropin on intestinal phytase activity and in vivo phytate hydrolysis in hybrid striped bass Morone chrysops × M. saxatilis

It has been recently demonstrated that hybrid striped bass Morone chrysops × M. saxatilis exhibit intestinal phytase activity, an enzyme capable of liberating inorganic orthophosphate from the phytate molecule, thereby making phytate phosphorus (PP) available for absorption and utilization by the fish. However, it was also determined that hybrid bass were able to digest only 1–2% of dietary PP. Therefore, an experiment was conducted to determine if exogenously administered recombinant bovine somatotropin (rbST) would increase intestinal phytase activity in hybrid striped bass to a level that would improve PP availability. The results indicate that exogenous rbST treatment, administered either through intraperitoneal injection or orally, does increase intestinal brush border membrane protein concentration. While injection with rbST led to significant increases in both specific brush border membrane and total intestinal phytase activity, oral rbST administration did not cause similar increases. Total P and PP digestibility were not influenced by rbST administration. While treatment with rbST does have the potential to enhance intestinal phytase activity in hybrid striped bass, it does not appear to increase PP digestibility. This observation limits the hormone's utility as an effective technique for improving PP bioavailability to this species.     

Trophic dynamics of a reservoir fishery following an introduction of a top predator: Insights from stable carbon and nitrogen isotopes

Trophic dynamics and conceptual niche spaces of top piscivores were assessed using stable isotope analysis following the introduction of hybrid striped bass Morone saxatilis (Walbaum) × Morone chrysops (Rafinesque) into an established reservoir fishery devoid of gizzard shad, Dorosoma cepedianum (Lasueur). Hybrid striped bass were initially stocked into Three Mile Lake, Iowa as an attempt to biologically control pervasive yellow bass, Morone mississippiensis Jordan & Eigenmann, populations. From the analyses, it concluded that hybrid striped bass predominately targeted prey fish located in the littoral habitats of the reservoir and did not selectively consume yellow bass as intended. Bayesian isotope mixing models described the diets of hybrid striped bass to include a variety of prey fish, predominantly consisting of young bluegill Lepomis macrochirus and yellow bass. Food resource overlap among hybrid striped bass, largemouth bass, Micropterus salmoides Lacépède, and walleye, Sander vitreus (Mitchill), appeared substantial based on the isotopic niche overlap model. Results from this case study, in conjunction with the hindsight that yellow bass populations became prolific even with stockings of hybrid striped bass, suggest that their use to control yellow bass populations may not be a viable management strategy in southern Iowa.     

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.     

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.     

Sedation by Orally Administered Ketamine in Goldfish,Carassius auratus; Hybrid Striped Bass,Morone hybrid saxatilis×M. chrysops; and Ocellated River Stingray,Potamotrygon motoro

With the continued popularity of pet aquaculture and concurrent demands for advances in veterinary medicine of fish species, a need exists for a reliable, safe, and environmentally noncontaminating method of sedation. With appropriate sedation, fish can be more safely transported or handled for veterinary care. Sedation can minimize stress or physical damage caused by handling and capture, and prepare fish for the deeper planes of anesthesia necessary for more extensive handling, longer transport, or invasive procedures. This study assessed the efficacy of ketamine as a sedative when administered orally to three species of fish: common goldfish, Carassius auratus, ocellated river stingray, Potamotrygon motoro, and hybrid striped bass, Morone saxatilis×Morone chrysops. A practical application opportunity that became available at the end of the study demonstrated the use of oral ketamine in the transport of a single arapaima, Arapaima gigas.     

Comparison of Growth Between Morone Hybrids (Palmetto and Sunshine) in Earthen Ponds

Palmetto bass are produced by crossing the female striped bass, Morone saxatilis, with the male white bass, Morone chrysops; whereas, the sunshine bass is the reciprocal cross. The hybrid striped bass industry typically rears sunshine bass in earthen ponds, because of the ease of handling, availability, and early maturation of the white bass female broodstock. Growth performance has been assumed similar between the crosses. Under commercial pond conditions, sunshine bass (19.8 ± 0.4 g (mean ± SEM)) and palmetto bass (23.2 ± 0.3 g) were grown to market size (617.0 ± 17.2 g sunshine and 620 ± 3.6 g palmetto) within 15 mo, yielding 4532.6 kg/ha. The net production between the crosses was not significantly different and averaged 4373.4 kg/ha. Feed conversion ratio (FCR) of sunshine bass (FCR 1.70) was better (P = 0.0158) than palmetto bass (FCR 1.76). Commercial processing metrics of each cross demonstrated significant differences, with sunshine bass exhibiting lower frame waste (P = 0.0457) than palmetto bass, probably due to fish body shape or conformational differences at this size. Without growth performance differences between the hybrids, there might be an advantage to rearing sunshine bass due to the slightly better FCR and increased skinless boneless fillet yield.     

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.     

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.     

The Modification of Poultry By-product Meal for Use in Hybrid Striped Bass Morone chrysops×M. saxatilis Diets

Abstract— A pair of experiments were performed to assess amino acid supplementation of pet food grade poultry by‐product meal for utilization as the sole protein source for hybrid striped bass Morone chrysops×M. saxatilis. The first experiment determined the available amino acids from menhaden fishmeal and poultry by‐product meal for hybrid striped bass. The second experiment determined the efficacy of supplementing poultry by‐product meal with amino acids based on an ideal amino acid profile of hybrid striped bass muscle. The positive control diet contained 40% digestible protein solely from menhaden fishmeal and the negative control diet contained 40% digestible protein solely from pet food grade poultry by‐product meal. The negative control diet was additively supplemented with lysine, methionine, threonine, and leucine at 1.16,0.57,0.31 and 0.47% of the diet, respectively. Lysine supplementation alone did not improve fish performance based on any measured response. Moreover, the negative control diet and the lysine supplemented diet had lower weight gain and feed efficiency than the positive control diet. Supplementation of the diet containing pet food grade poultry by‐product with lysine and methionine; lysine, methionine, and threonine; or lysine, methionine, threonine, and leucine improved weight gain and feed efficiency above that of the negative control diet. The diet containing poultry by‐product supplemented with lysine, methionine, and threonine produced weight gains statistically indistinguishable from those of the positive control diet. Protein and energy retention efficiencies also improved with supplementation of at least lysine and methionine and were statistically indistinguishable from those observed in fish fed the positive control diet. Supplementation with lysine and methionine reduced the hepatosomatic index to levels similar to those found in fish fed the menhaden fishmeal diet. Intraperitoneal fat levels were similar among treatments (6.1‐6.6%) with the exception that fish fed the diet supplemented with lysine, methionine, and threonine exhibited lower (5.5%) fat levels. Supplementing the poultry by‐product meal diet with only lysine and methionine increased muscle ratio to levels equivalent to those found in fish fed the positive control (fishmeal) diet. In conclusion, amino acid supplementation of pet food grade poultry by‐product meal can be used to replace fishmeal in diets for hybrid striped bass without a reduction in fish performance.     

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.     

Transmission of infectious pancreatic necrosis virus in striped bass, Morone saxatilis (Walbaum)

Abstract. Infectious pancreatic necrosis virus (IPNV) did not cause increased mortality in experimentally challenged striped bass, Morone saxatilis (Walbaum). Fry became transiently infected after waterborne challenge but fingerlings were resistant to that route. However, striped bass fingerlings readily became chronic virus carriers following ingestion of IPNV-contaminated food. Vertical transmission was not demonstrated using either IPNV-carrier striped bass adults or IPNV-exposed sex products.     

Dietary Zinc Requirement of Hybrid Striped Bass,Morone chrysops×Morone saxatilis,and Bioavailability of Two Chemically Different Zinc Compounds

Zinc is a trace mineral element that plays an essential role in numerous biochemical processes, and has been shown to affect growth and health of several fish species. However, the dietary zinc requirement of hybrid striped bass has not been defined. Therefore, a feeding trial was conducted to determine the dietary requirement for zinc by this fish and to compare zinc bioavailability of two chemically different forms (zinc sulfate and zinc proteinate). Six experimental diets were formulated with purified ingredients and supplemented with ZnSO₄ to provide total zinc concentrations of 7, 12, 16, 26, 42, and 80 mg/kg diet which were determined by analysis. Each diet contained 32% crude protein, 6% lipid, and approximately 14.2 kJ of digestible energy per gram. The experimental diets were fed twice daily for 10 wk to triplicate groups of 15 hybrid striped bass initially weighing 0.86 ± 0.05 g/fish in 38‐L glass aquaria, connected as a recirculating system. Finally, after the feeding period, the fish were evaluated for weight gain, feed efficiency, protein efficiency ratio, and survival, as well as blood serum zinc, bone zinc, and hematocrit. All fish thrived during the feeding trial and not even the fish fed the basal diet displayed any apparent deficiency signs, although weight gain steadily increased with escalating levels of dietary zinc up to 42 mg/kg diet. On the basis of the most responsive indicators–bone zinc and serum zinc–the minimum dietary zinc requirement of hybrid striped bass was determined to be 17.0 and 17.3 mg Zn/kg diet, respectively, based on broken‐line regression. This estimate is similar in magnitude to dietary zinc requirements reported for other fish species. In addition, the bioavailability of zinc proteinate versus that of ZnSO₄ was estimated by deriving the ratio of the slopes of the regression lines fitted to bone zinc and serum zinc data. This analysis indicated that hybrid striped bass utilized zinc proteinate ～1.7 times more efficiently than ZnSO₄.     

Evaluation of Three Soybean Products in Diets Fed to Juvenile Hybrid Striped Bass Morone saxatilis×M. chrysops

Juvenile hybrid striped bass Morone saxatilis×M. chrysops were fed practical diets containing graded levels of either solvent-extracted soybean meal, roasted soybeans, or raw, unprocessed soybeans. Two separate 10-wk studies were conducted; within each study, there were two separate evaluations of soy products. In the first study, weight gain and feed efficiency of fish fed 45% or higher levels of soybean meal were significantly lower than fish fed the positive control diet, while weight gain and feed efficiency of fish fed 30% soybean meal were not significantly different than fish fed the control diet. Fish fed the lowest level of unprocessed soybean (20%) exhibited significantly depressed weight gain and feed efficiency compared to fish fed the control diet. In the second study, weight gain and feed efficiency of fish fed 40% roasted soybeans were significantly lower than fish fed the control diet, but weight gain and feed efficiency of fish fed 20% roasted soybeans were not significantly lower than fish fed the control diet. In both studies, whole body proximate composition values were significantly different among treatments. Whole-body lipid concentrations were significantly higher in fish fed certain levels of soy products, but only at levels above those eliciting depressions in weight gain and feed efficiency. A further evaluation of solvent-extracted soybean meal was conducted with incorporation levels of 20–40% of the dry diet in gradations of 5% with a nutritionally complete mineral premix. Weight gain and feed efficiency of fish fed any level of soybean meal in that study were not significantly different from fish fed a positive control diet. Whole body proximate components were not significantly different between treatments. Unprocessed soybeans apparently have little potential as an ingredient in diets fed to juvenile hybrid striped bass; roasting, or heat treatment, improves their use. Solvent extracted soybean has the potential of supplying the majority of crude protein in diets fed to juvenile hybrid striped bass. Incorporation of complete mineral premixes seems beneficial with higher levels of solvent-extracted soybean meal.     

Hypoxia affects performance traits and body composition of juvenile hybrid striped bass (Morone chrysops × M. saxatilis)

Performance traits and body composition of juvenile hybrid striped bass (Morone chrysops × M. saxatilis) in response to hypoxia were evaluated in replicate tanks maintained at constant dissolved oxygen concentrations that averaged 23.0 ± 2.3%, 39.7 ± 3.0% and 105.5 ± 9.5% dissolved oxygen saturation. Fish were fed a commercially formulated feed daily to apparent satiation. Total feed intake and fish growth and yield increased linearly in response to increased dissolved oxygen concentration. Nutrient utilization was reduced significantly only at the greatest level of hypoxia. With the exception of whole body protein content, whole body compositional indices and nutrient retention efficiencies were linearly related to dissolved oxygen concentration. Results demonstrate that as hypoxia becomes more severe, juvenile hybrid striped bass feed intake is reduced, which affects growth and nutrient retention.     

Ration of 20:3 (n-9) to 20:5 (n-3) in Phospholipids as an Indicators of Dietary Essential Fatty Acid Sufficiency in Striped Bass,Morone saxarilis,and Palmetto Bass,M. saxatilis x M. chrysops

The effects of feeding different sources of brine shrimp nauplii with different fatty acid compositions on growth, survival, and fatty acid composition of striped bass, Morone saxarilis and palmetto bass (M. saxatilis x M. chrysops) were determined. The sources of brine shrimp were Chinese (CH), with a high percentage of 20:5(n-3), eicosapentaenoic acid (EPA), and Colombian (COL), San Francisco Bay (SFB), and Great Salt Lake (GSL), with low percentages of EPA but high percentages of 18:3(n-3), linoienic acid. None of the brine shrimp sources contained a measurable amount of 22:6(n-3), docosahexaenoic acid (DHA). After enrichment with menhaden oil to increase the content of EPA and DHA, the GSL brine shrimp nauplii were also fed to hybrid striped bass.Growth and survival of fish larvae fed brine shrimp nauplii with high percentages of EPA and DHA (CH and GSLE) were higher (P < 0.05) than those of fish fed brine shrimp with a low percentage of EPA (COL, SFB, and GSL). The ratio of 20:3(n-9) eicosatrienoic acid (ETA), to DHA in polar lipids (phospholipids) of fish, traditionally used as an indicator of essential fatty acid (EFA) sufficiency of the diet, was not a reliable indicator of essential fatty acid sufficiency of diets for larval striped bass and hybrid striped bass. However, the ratio of ETA to EPA appears to be an appropriate indicator. An ETA-to-EPA ratio in phospholipids of less than 0.10 is consistent with an EFA sufficient diet.     

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.