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The vasa gene, encoding an ATP-dependent RNA helicase, and the nanos-2 gene, an RNA-binding protein, are essential for germ cell origination, migration, maintenance, and development in vertebrates and invertebrates. The expression levels of the vasa and nanos-2 genes have not yet been investigated or reported in crappie species. These two genes were partially sequenced and characterized, and their expression patterns were analyzed using reverse-transcription quantitative polymerase chain reaction (RT-qPCR) according to age and sex. The vasa sequences of white crappie (WC) females and males showed significant similarity with the vasa homologs of largemouth bass (Micropterus salmoides; 93.1–93.98%) and smallmouth bass (M. dolomieu; 91.95–92.77%), indicating its conserved nature within the Family Centrarchidae. The vasa sequence of black crappie (BC) females showed significant similarity with the vasa homologs of white crappie (91.67%), largemouth bass (96.10%), smallmouth bass (96.10%), spotted scat (Scatophagus argus; 97.37%), mandarin fish (Siniperca chutasi; 96.15%), Japanese sea bass (Lateolabrax japonicus; 94.87%), lumpfish (Cyclopterus lumpus; 91.95%), southern bluefin tuna (Thunnus maccoyii; 94.74%), large yellow croaker (Larimichthys crocea; 92.21%), and Nile tilapia (Oreochromis niloticus; 92.21%). The nanos-2 sequences of WC females, WC males, and BC females showed significant similarity with the nanos-2 of largemouth bass (92.92–96.36%), smallmouth bass (92.92–96.36%), and mandarin fish (92.66–94.34%). The expression of vasa in BC females was significantly higher at age-2 than at age-1, while WC males and females presented no significant age-related differences. Neither species had a significant difference in nanos-2 gene expression with age. The expression levels of vasa and nanos-2 were significantly higher in WC males than females. [ABSTRACT FROM AUTHOR]

Flavobacterium covae (columnaris) is the most detrimental bacterial disease affecting the largemouth bass (Micropterus salmoides Lacépède) aquaculture industry. In the current study, fish received an intraperitoneal injection of either 1× PBS (100 μL), LPS in PBS (100 μL, 10 μg/mL), or F. covae (100 μL, 2.85 × 1011 CFU/mL) to simulate immunological challenges. After 24 h post‐injection, liver tissue from the control and treated groups were then collected for transcriptome analysis. Results of the Gene Ontology (GO) and KEGG pathway analyses for the F. covae and LPS‐injected groups found differentially expressed genes (DEGs) enriched primarily in toll‐like receptors (TLRs), cytokine–cytokine receptors, complement and coagulation cascades, and the PPAR signalling pathways. This suggests that the liver immune system is enhanced by these five combined pathways. Additionally, the DEGs TLR5, MYD88, and IL‐1 were significantly upregulated in F. covae and LPS‐injected fish compared to the controls, whereas IL‐8 was downregulated. The upregulation of TLR5 was unexpected as F. covae lacks flagellin, the protein that binds to TLR5. Additionally, it is unknown whether the TLR5 is upregulated by LPS. Further research into the upregulation of TLR5 is warranted. These results provide insight into immune responses and associated pathways contributing to the immune system in the liver during columnaris infection and induced response to LPS in largemouth bass. [ABSTRACT FROM AUTHOR]

Investigations were conducted to develop a general protocol for the isolation and in vitro culture of ovary‐derived cells from black crappie, Pomoxis nigromaculatus, and white crappie, P. annularis. Five digestive enzymes: 500 U/mL collagenase type I, 500 U/mL collagenase type IV, 0.05% trypsin‐EDTA, 0.25% trypsin‐EDTA, and 1X TrypLE™ Express were evaluated for live cell isolation. The isolated cells were cultured in 10 or 20% fetal bovine serum (FBS) in L‐15 growth media. In addition, four incubation temperatures (15°C, 20°C, 25°C, and 30°C) were also evaluated. The number of live cells obtained from the 0.25% trypsin and TrypLE™ Express treatments was significantly higher than other treatments. No difference in cell growth was observed between the two FBS treatments. Cells isolated using TrypLE™ Express and 0.25% trypsin reached 80% to 90% confluency in 12.5 cm2 cell culture flasks within 5 days of inoculation at 20 and 25°C. At 15°C, 10 days were required to reach 80%–90% confluency. Morphologically, cells incubated at 15°C, 20°C, and 25°C appeared healthier than cells incubated at 30°C, where irregular cell shape and substrate detachment were observed. We concluded TrypLE™ Express and 0.25% trypsin were optimal for cell dissociation and isolation of crappie ovarian cells. An incubation temperature of 20°C–25°C was favorable for cell culture in L‐15 media supplemented with either 10% or 20% FBS. [ABSTRACT FROM AUTHOR]

This study was carried out to test the suitability of biofloc technology to improve the productivity of the fathead minnow, Pimephales promelas, a commercially important baitfish in North America. Biofloc growth was induced in treatment tanks by periodic additions of a carbon source (glucose) to maintain a C : N ratio of 12:1. Control tanks (no aeration and no carbon addition) accommodated densities equivalent to 1 million fish/ha, while treatment tanks (biofloc) had densities of 1, 2, 4, and 8 million fish/ha. Fish were fed 4% body weight using a 32% protein commercial diet. There were no significant differences in condition of fish harvested from control and treatment densities ( P < 0.05). However, fish growth indicators such as final individual weight, feed conversion efficiency, and specific growth rate were significantly impaired at higher stocking densities. Survival rate was significantly lower in the 8 million/ha treatment ( P < 0.05). Results were indicative of possible production efficiencies of twofold higher in biofloc systems stocked at or below 4 million/ha compared with traditional ponds. Although biofloc systems maintained the desired water-quality parameters, biofloc microbial biomass did not seem to significantly enhance feed conversion and specific growth rates of fathead minnows. [ABSTRACT FROM AUTHOR]

Alternative management strategies will be required to produce hybrid catfish (♂Ictalurus punctatusX ♀Ictalurus furcatus) year-round to provide continuous market supply. Hybrid catfish fingerlings were stocked at 9,880 head/ha singly or in co-culture with sub-marketable (mean weight = 454 ± 16 g) hybrid catfish carried over the winter from a previous year’s multi-size trial. Economic analyses compared cost of production ($/kg of market-size fish produced) and cash flow of single- and multiple-batch production of hybrid catfish for a single- and two-year period. Gross total and marketable yields were significantly greater in the mixed-size treatment as compared to the single-size treatment, in spite of the significantly greater percentage of market-size fish (84%) in the single-size treatment than in the mixed-size treatment (71%). Cost of production ($/kg) was 4% to 10% lower in the multi-size treatment in the single-year analysis, but 18% to 20% lower when the full two-year cycle was assessed. Cash flow and cash flow risk were improved substantially with the multi-size treatment primarily because the overwintered sub-market-size fish from the previous year reached market size three to four months earlier than in the single-size treatment. [ABSTRACT FROM PUBLISHER]

The main objectives of this study were to approximate the maximum yield and evaluate size dispersion of stocker size largemouth bass, Micropterus salmoides reared in a semi-closed recirculating system for 60 days. Fingerlings with an average body weight of 36.7 g were utilized for the study. An experimental system consisting of 18 square plastic tanks (165 L) equipped with a radial flow settler, a sump, a moving bed filter, a centrifugal pump, a rapid sand filter, a down-flow oxygen saturator and a UV sterilizer was utilized for the trial. The system was operated semi-closed, accounting for a daily exchange rate of 30-50% of total system water volume. Experimental stocking densities were 4.5, 9.1, 18.8, 36.5, 54.6 and 73 kg m−3 with three replicates per treatment. At the end of the experimental trial, largemouth bass showed acceptable feed conversion (1.00-1.48), specific growth rate (1.16-1.45% day−1) and survival rate (81.8-96.6%) in all treatments, displaying the highest performance at an initial stocking density range of 18-36 kg m−3. Based on a piecewise regression model with breakpoint analysis, maximum yield of largemouth bass fingerlings should not exceed 70 kg m−3. As stocking density increased, relatively more underweight fingerlings were produced with a higher uniformity of fatness. [ABSTRACT FROM AUTHOR]

Most hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, producers stock 18- to 19-cm fingerlings in single-batch production. While stocking smaller fingerlings would be less expensive, the economic trade-offs of using smaller fingerlings is unknown. Two sizes of hybrid catfish fingerlings (13-cm and 19-cm) were stocked in single-size treatments at 9884 head/ha and a multi-size treatment with each size stocked at 9884 head/ha (total 19,768 head/ha). In the 13-cm and 19-cm single-size treatments, 87 and 98%, respectively, reached market size in one season. In the multi-size treatment, 77% of all fish stocked reached market size, demonstrating that more than half of the 13-cm fish reached market size in this treatment. Gross, net, and marketable yields were significantly greater in the multi-size treatment when compared to the 13-cm or 19-cm single-size treatments, but were not significantly different between the two single-size treatments. The 19-cm single-size treatment resulted in greater break-even prices and economic risk than the other two treatments. This study demonstrated that 13-cm hybrid catfish fingerlings can be raised economically in both single- and multi-size production systems in the southern USA. [ABSTRACT FROM AUTHOR]