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.     

Development and testing of a pedigree‐marking system using visible implant elastomer tags for selective improvement in Morone breeding programmes

The development and testing of a visible implant elastomer pedigree‐marking system was evaluated in sunshine bass, Morone chrysops×Morone saxatilis, and white bass, M. chrysops (Rafinesque). These tags were tested in sunshine bass fingerlings at one of four subdermal body locations (posterior to the eye, dorsal fin musculature, caudal fin musculature or anal fin musculature). Tag visibility decreased with increased sunshine bass growth (63% after 56 days). Visibility differed among body locations, with the caudal and anal tagging locations having lower visibility. White bass fingerlings representing eight genetic groups were then tagged at one of two body locations (left or right subdermal along the dorsal musculature) using one of four fluorescent colours and reared for 42 days in a common garden growth trial. Tag visibility in white bass was 99.5% at 14 days, 98.2% at 28 days and 94.9% at 42 days after tagging. There was a significant change in weight among the eight genetic groups of white bass fingerlings after 42 days (P=0.03). Testing of this pedigree tagging system successfully identified phenotypically different groups of white bass fingerlings.     

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.     

Infections with Philometra sp. associated with mortalities in wild-hatched captive-raised striped bass, Morone saxatilis (Walbaum)

The striped bass, Morone saxatilis (Walbaum), once represented an important resource for fisheries in the St Lawrence River (Quebec, Canada). A restoration programme, involving captive propagation, was implemented with the objective of restocking the population, which had disappeared in the late 1960s. An unusually high rate of mortality was observed during the winter of 2006 in captive-raised fingerlings that were originally collected from the Miramichi River (New Brunswick, Canada) the previous summer. Post-mortem examinations revealed extensive granulomatous and hyperplastic peritonitis associated with numerous nematodes of the genus Philometra. Given the severity of the lesions, high intensity of infection by Philometra sp. was presumed to be the primary factor in the unusual mortalities reported that winter. Observations suggest that this nematode, which was acquired in the wild, cannot establish itself in a captive environment, most likely because of the absence of the obligate intermediate host. Examination of archived specimens of striped bass showed that this parasite was probably present in the St Lawrence River population prior to its extirpation. Consequently, the introduction of infected fish into this ecosystem should not be a concern. Nevertheless, infection-related mortalities of fingerlings might affect dynamics of wild striped bass populations.     

Influence of temperature and salinity on length and yolk utilization of striped bass larvae

The effects of temperature and salinity on yolk utilization and growth of larval striped bass (Morone soxatilis) from Canadian maritime stocks were studied to determine optimal rearing conditions. Larval length increased during yolk utilization and maximum length (L_max) was attained at about 70 degree-days post-hatch. Dry weight declined during yolk utilization, whereas, larval wet weight was relatively constant and only declined when yolk was depleted. Temperature and salinity significantly affected the L_max. Temperatures exceeding 18 C resulted in lower L_max. Higher L_max values were attained at 5 % than at 1 or 10 %. Time to reach L_max was longer at 5 and 10 % than at 1 % for any experimental temperature. Time to reach L_max was 3 days post-hatch longer than times to maximum embryo dry weight. The Q₁₀ of yolk utilization was 1.71, 1.53 and 2.52 at 1, 5 and 10 %, respectively. Times to terminal yolk utilization were about 1.2 d shorter than times to L_max. Morphological changes during yolk utilization indicated rapid development of locomotory and predatory capabilities. These and other developmental strategies were compared to those of salmonids. Rearing striped bass larvae at 14 \-16C and 5 % throughout yolk utilization should result in longer larvae at initial first feeding.     

Production performance, stress tolerance and intestinal integrity of sunshine bass fed increasing levels of soybean meal

Soybean meal (SBM) is perhaps the most common fish meal (FM) alternative used in aquafeeds; however, SBM cannot fully replace FM in sunshine bass Morone chrysops × M. saxatilis feeds without impacting growth. Reduced production performance may be the result of subtle changes in morphology and/or physiological status. Accordingly, our objective was to assess growth, gastrointestinal integrity and stress tolerance of sunshine bass fed increasing amounts of SBM. Fish (approximately 14.5 g) were fed diets (14% lipid and 40% protein) containing increasing amounts of SBM at the expense of FM (30% FM, 20% FM, 15% FM, 10% FM, 5% FM and 0% FM) for 8 weeks. As expected, complete replacement of FM reduced growth. Although some signs of enteritis were noted, no significant differences in gut integrity were observed. Following 15-min low-water stress challenge, plasma glucose levels were elevated, particularly among fish fed increasing amounts of SBM. Cortisol response was similar, but statistical differences were not resolved for this parameter. Completely replacing FM in feeds for sunshine bass elicits overt reductions in growth. More subtle physiological changes may also result from FM replacement, including alterations in stress tolerance, and these may be important to consider in terms of the suitability of aquafeed formulations and optimal nutrition of sunshine bass.     

Understanding imperfect detection in a San Francisco Estuary long‐term larval and juvenile fish monitoring programme

Imperfect detection can present a significant challenge when monitoring for a rare and imperilled species. Here, a long‐term larval and early‐juvenile fish monitoring programme in the upper San Francisco Estuary was examined to evaluate its overall reliability in detecting various fish species, including the imperilled delta smelt, Hypomesus transpacificus McAllister, for which the programme was designed. Using occupancy modelling, detection probability of species with pelagic larval or juvenile life stages was found to be generally high (≥.95) based on the current sampling effort of three larval net tows per site. However, detection probability can vary considerably from year to year depending on the species’ level of larval production. Water temperature and turbidity were identified as important predictors of occurrence for young‐of‐year delta smelt, longfin smelt Spirinchus thaleichthys (Ayres) and striped bass Morone saxatilis (Walbaum), and there was evidence for fish size selectivity by the sampling gear in all three species. These results highlight the need to consider adaptively managing detection probability by increasing sampling effort in years when young‐of‐year delta smelt abundance is expected to be low, especially when information on the species’ occurrence at a particular region is critical.     

Effects of replacing fish meal with poultry by‐product meal and soybean meal and reduced protein level on the performance and immune status of pond‐grown sunshine bass (Morone chrysops × M. saxatilis)

Two primary ways to achieve low‐cost, nutritionally efficacious diets for sunshine bass (Morone chrysops × M. saxatilis) are to decrease crude protein (CP) levels and the use alternative animal or plant ingredients to partially, or totally, replace fish meal. A 459‐day feeding trial was conducted with juvenile (35 g) sunshine bass to evaluate growth, feed efficiency, size distribution at harvest, immune function status and body composition when fed diets containing soybean meal (SBM), feed‐grade poultry by‐product meal (PBM), and supplemental methionine as complete replacements for menhaden fish meal (MFM) at 300 g kg^?1 diet, while simultaneously reducing dietary crude protein (CP; 320, 360, and 400 g kg^?1). The feeding trial was conducted in 12, 0.04‐ha earthen ponds stocked at a rate of 300 per pond (3000/ac). At 400 g kg^?1 dietary protein, there were no differences in responses between fish fed the diet containing MFM or the diet in which MFM was completely replaced with PBM and supplemental methionine on a digestible protein basis. However, final mean weight, percentage weight gain, specific growth rate, and protein efficiency ratio were linearly related (P < 0.10) to dietary protein level in the diets while no significant differences were found in feed intake and feed conversion ratio. The expected odds of fish at harvest being classified into larger size categories (> 680 g) decreased as dietary protein level decreased based on ordinal logistic regression. There were no significant relationships between body compositional indices and dietary treatments. Body fat ranged from 56 g kg^?1 to 62 g kg^?1, single fillets ranged from 28% to 30%, and livers ranged from 2.45% to 2.62% of body weight across treatments. Fillet protein concentration was positively linear and quadratic for protein level in the diet but fillet moisture, lipid and ash did not differ among diets. Total serum protein, immunoglobulin and lysozyme activity decreased linearly with decreasing diet protein level. These results suggest that complete replacement of MFM with feed grade PBM and supplemental methionine is possible in diets for sunshine bass and that further reductions in dietary protein level may be possible with amino acid supplementation.     

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.