A preliminary study of dietary protein requirement of juvenile marbled flounder (Pseudopleuronectes yokohamae)

An 8-week feeding trial was conducted to determine the optimal dietary protein level for juvenile marbled flounder. Five semi-purified test diets were formulated to contain different protein levels (CP) including 42.7%, 47.4%, 53.3%, 58.8%, and 64.5% (dry matter), named as CP42.7, CP47.4, CP53.3, CP58.8, and CP64.5, respectively. Five hundred and twenty-five juveniles (6.0 ± 0.1 g) were randomly distributed into 15 tanks (300 L tanks), resulting in 35 fish per tank (n = 3 tanks). Fish were fed the test diets 5 times per day until satiation. The CP58.8 resulted in the highest gain in weight and the best efficiency in feed utilization among the tested protein levels (P < 0.05). Fish fed the CP58.8 diet showed significantly higher whole-body protein and lipid contents than the fish that were fed the other diets (P < 0.05). Fish fed the CP53.3, CP58.8, and CP64.5 diets showed a significantly higher dorsal-muscle lipid content than the fish that were fed the CP42.7 and CP47.4 diets (P < 0.05). The one-slope straight broken-line regression analysis on the results of the thermal growth coefficient and feed conversion ratio indicated that the estimated optimum dietary protein level was 58.8%. Taken together, it is suggested that the dietary protein level of 58.8% is optimal for better growth and high efficiency in feed utilization for the juvenile marbled flounder.     

Comparison of Tank Treatments with Copper Sulfate and Potassium Permanganate for Sunshine Bass with Ichthyobodosis

Abstract

The biflagellated, single-celled parasite Ichthyobodo necator can cause significant losses among fish populations, particularly those cultured in tanks. Treatments of KMnO₄ and CuSO₄ were evaluated against a naturally occurring I. necator infestation on sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) raised in tanks. Four-hour static treatments with 3 mg of KMnO₄/L of water (2.5 mg/L above the determined KMnO₄ demand) or 2 mg of CuSO₄/L of water (total alkalinity = 207 mg/L; total hardness = 95 mg/L) were randomly applied to 4 tanks/treatment (23 fish/tank); the same treatments were reapplied 2 d later. Four tanks were used as positive controls. By 2 d posttreatment (after the second treatment), only 17.4% of the untreated control fish survived, and a sample of the remaining fish was heavily infested with I. necator. All remaining control fish were dead by 5 d posttreatment. The KMnO₄ treatment significantly curtailed the initial mortality (survival = 92.4%) and slightly reduced the high parasite loads at 2 d posttreatment. However, fish mortalities increased dramatically over the next 3 d (survival at 5 d posttreatment = 37.5%), and parasite loads from sampled fish remained high. The CuSO₄ treatment was effective in significantly lowering the parasite load (almost eliminating I. necator) and maintaining a high fish survival (87.5%) by 5 d posttreatment. The findings in this study clearly demonstrate that CuSO₄ is a viable treatment for ichthyobodosis in tanks.     

Determination of florfenicol dose rate in feed for control of mortality in Nile tilapia infected with Streptococcus iniae

A dose titration study was conducted to determine the dosage of florfenicol (FFC) in feed to control Streptococcus iniae-associated mortality in Nile tilapia Oreochromis niloticus. Six tanks were assigned to each of five treatments: (1) not challenged with S. iniae and fed unmedicated feed; (2) challenged with S. iniae by injection and fed unmedicated feed; (3) challenged with S. iniae and given FFC at 5 mg/kg of body weight (bw) in medicated feed; (4) challenged with S. iniae and given 10 mg FFC/kg bw; and (5) challenged with S. iniae and given 15 mg FFC/kg bw. Treatment was initiated the day after inoculation, and feed was administered for 10 d. Cumulative mortality was 0% in the unchallenged, untreated group; 35.8 +/- 4.4% (mean +/- SE) in the challenged, unmedicated group; 19.2 +/- 2.7% in the 5-mg/kg treated group, 12.5 +/- 3.8% in the 10-mg/kg group, and 2.5 +/- 1.1% in the 15-mg/kg group. The cumulative mortality was significantly less in each challenged, FFC-treated group than in the challenged, unmedicated controls (5 mg/ kg: P = 0.0156; 10 mg/kg: P = 0.0007; 15 mg/kg: P < 0.0001). The efficacy of the 10- and 15-mg/kg FFC dosages was studied in a separate dose confirmation study. Fish in all tanks were injected with S. iniae. At 4 h postinoculation, 10 tanks were assigned to each of three feed treatments: (1) unmedicated feed; (2) 10 mg FFC/kg bw; and (3) 15 mg FFC/kg bw. Cumulative mortality was 20.5 +/- 2.0% in the challenged, unmedicated group; 11.0 +/- 2.1% in the 10-mg/kg group; and 5.5 +/- 2.4% in the 15-mg/kg group. Mortality was significantly less in the medicated groups than in the challenged, unmedicated control group (10 mg/kg: P = 0.0270; 15 mg/kg: P = 0.0007). Fish in both studies were necropsied, cultured for bacteria, and examined for gross lesions. The minimum inhibitory concentration of FFC against S. iniae in both studies ranged from 0.5 to 1.0 microg/mL. Florfenicol was palatable, safe, and efficacious for control of Nile tilapia mortality due to S. iniae infection.     

Effects of metomidate hydrochloride sedation on blood glucose and marketability of transported threespot gourami Trichogaster trichopterus

Our objectives were to determine whether sedation with metomidate hydrochloride (hereafter, "metomidate") during transportation of threespot gourami Trichogaster trichopterus would prevent an increase in blood glucose levels and improve fish marketability (i.e., based on appearance and behavior) in comparison with unsedated controls. Threespot gourami are obligate air-breathers that possess a labyrinth organ, enabling the fish to respire air above the water surface; these fish should be lightly sedated during transport. Fish were transported for approximately 24 h via truck and domestic airline. Blood was sampled at 0, 2, 6, and 12 h posttransport ation, and appearance and behavior were observed at 0, 2, 4, 6, and 12 h and 7 d posttransportation. Metomidate concentrations tested were 0.0 (control), 0.1, 0.2, 0.3, and 0.4 mg/L. At the concentrations tested, metomidate neither inhibited elevations in blood glucose nor improved marketability. Fish that were transported with 0.3-mg/L metomidate were less marketable based on behavioral indices, and fish that were transported with 0.4-mg/L metomidate had higher glucose levels than control fish. Use of metomidate as a transport sedative for threespot gourami should be considered with caution and may be problematic at the concentrations tested; however, further research examining additional indices of stress may clarify metomidate use for this species.     

Survey of Pathogens in Hatchery Chinook Salmon with Different Out-Migration Histories through the Snake and Columbia Rivers

The operation of the Federal Columbia River Power System (FCRPS) has negatively affected threatened and endangered salmonid populations in the Pacific Northwest. Barging Snake River spring Chinook salmon Oncorhynchus tshawytscha through the FCRPS is one effort to mitigate the effect of the hydrosystem on juvenile salmon out-migration. However, little is known about the occurrence and transmission of infectious agents in barged juvenile salmon relative to juvenile salmon that remain in-river to navigate to the ocean. We conducted a survey of hatchery-reared spring Chinook salmon at various points along their out-migration path as they left their natal hatcheries and either migrated in-river or were barged through the FCRPS. Salmon kidneys were screened by polymerase chain reaction for nine pathogens and one family of water molds. Eight pathogens were detected; the most prevalent were Renibacterium salmoninarum and infectious hematopoietic necrosis virus. Species in the family Saprolegniaceae were also commonly detected. Pathogen prevalence was significantly greater in fish that were barged through the FCRPS than in fish left to out-migrate in-river. These results suggest that the transmission of infectious agents to susceptible juvenile salmon occurs during the barging process. Therefore, management activities that reduce pathogen exposure during barging may increase the survival of juvenile Chinook salmon after they are released.

Received May 27, 2010; accepted January 17, 2011     

Effects of Metomidate Hydrochloride Sedation on Blood Glucose and Marketability of Transported Threespot Gourami Trichogaster trichopterus

Abstract

Our objectives were to determine whether sedation with metomidate hydrochloride (hereafter, “metomidate”) during transportation of threespot gourami Trichogaster trichopterus would prevent an increase in blood glucose levels and improve fish marketability (i.e., based on appearance and behavior) in comparison with unsedated controls. Threespot gourami are obligate air-breathers that possess a labyrinth organ, enabling the fish to respire air above the water surface; these fish should be lightly sedated during transport. Fish were transported for approximately 24 h via truck and domestic airline. Blood was sampled at 0, 2, 6, and 12 h posttransportation, and appearance and behavior were observed at 0, 2, 4, 6, and 12 h and 7 d posttransportation. Metomidate concentrations tested were 0.0 (control), 0.1, 0.2, 0.3, and 0.4 mg/L. At the concentrations tested, metomidate neither inhibited elevations in blood glucose nor improved marketability. Fish that were transported with 0.3-mg/L metomidate were less marketable based on behavioral indices, and fish that were transported with 0.4-mg/L metomidate had higher glucose levels than control fish. Use of metomidate as a transport sedative for threespot gourami should be considered with caution and may be problematic at the concentrations tested; however, further research examining additional indices of stress may clarify metomidate use for this species.

Received February 16, 2011; accepted December 18, 2011.     

Production of Ceratonova shasta Myxospores from Salmon Carcasses: Carcass Removal Is Not a Viable Management Option

Severe infection by the endemic myxozoan parasite, Ceratonova (synonym, Ceratomyxa) shasta, has been associated with declines in and impaired recovery efforts of populations of fall-run Chinook Salmon Oncorhynchus tshawytscha in the Klamath River, California. The parasite has a complex life cycle involving a polychaete worm host as well as a salmon host. Myxospore transmission of this parasite, from salmon to polychaete, is a life cycle step during which there is a potential for applied disease management. A 3-year data set on prevalence, intensity, and spore characteristics of C. shasta myxospores was obtained from adult Chinook Salmon carcasses surveyed in the main stem of the Klamath River and three of its tributaries, Bogus Creek and the Shasta and Trinity rivers. Annual prevalence of myxospore detection in salmon intestines ranged from 22% to 52%, and spore concentration values per intestinal scraping ranged from 3.94 × 10² to 1.47 × 10⁷ spores. A prevalence of 7.3% of all carcasses examined produced >5.0 × 10⁵ spores, and these carcasses with “high” spore counts accounted for 76–95% of the total spores in a given spawning season. Molecular analysis of visually negative carcasses showed that 45–87% of these samples had parasite DNA, indicating they contained either low spore numbers or presporogonic stages of the parasite. Myxospores were rarely found in carcasses of freshly spawned adults but were common in decomposed carcasses of both sexes. The date of collection or age (based indirectly on FL) did not influence detection. The longer prespawn residence time for spring-run Chinook Salmon compared with that for fall-run Chinook Salmon in the Trinity River was associated with higher spore loads. The dye exclusion method for assessing spore viability in fresh smears indicated an inverse relationship in spore integrity and initial spore concentration. A carcass-removal pilot project in Bogus Creek for 6 weeks in the fall of 2008 (907 carcasses removed) and 2009 (1,799 carcasses removed) failed to measurably influence the DNA quantity of C. shasta in targeted waters. Combined with the high numbers of carcasses that contributed myxospores, we therefore deemed that this labor-intensive approach is not a viable management option to reduce the infectivity of C. shasta in Chinook Salmon in the Klamath River.

Received January 23, 2015; accepted September 28, 2015     

Toxicity of Ammonia and Nitrite to Sunshine Bass in Selected Environments

Abstract

The effects of environmental calcium and salinity on toxicities of ammonia and nitrite for sunshine bass (female Morone chrysops × male M. saxatilis) were investigated, and the effects of pH, sodium chloride, and calcium chloride on uptake and depuration of ammonia and nitrite were characterized. The concentration of un-ionized ammonia-nitrogen (UIA-N) lethal to 50% of the fish within 96 h (96-h LC50) ranged from 0.32 to 0.60 mg/L and increased significantly with increased concentration of environmental calcium over the range tested (5–80 mg/L). The acute toxicity of UIA-N was not affected by salinity over the range tested (1–24 g/L), and the 96-h LC50 was 0.70 ± 0.04 mg UIA-N/L (mean ± SE) over all salinities tested. The rate and degree of ammonia uptake was greater at elevated environmental pH. Environmental pH did not affect the rate of depuration of ammonia. Environmental calcium did not affect nitrite toxicity, and the 96-h LC50 of nitrite-nitrogen (nitrite-N) was 12.8 ± 1.6 mg/L (mean ± SE) over all calcium concentrations tested. The 96-h LC50 of nitrite-N for fish acclimated to a salinity of 1 g/L was 35.0 ± 2.3 mg/L (mean ± SE), whereas LC50s of nitrite-N for fish acclimated to salinities of or higher than 8 g/L were greater than 100 mg/L (the highest exposure level). The addition of chloride to freshwater environments reduced the accumulation of nitrite in the plasma. Chloride was more effective in reducing the accumulation of nitrite in the plasma when added as calcium chloride rather than as sodium chloride. This study indicates that sunshine bass are relatively sensitive to both ammonia and nitrite. Tolerance to ammonia can be increased in freshwater environments by increasing calcium levels or decreasing environmental pH. Tolerance to nitrite can be increased by addition of chloride to freshwater environments or through the use of saltwater environments.     

Lack of Protection following Re-Exposure of Chinook Salmon to Ceratonova shasta (Myxozoa)

The recent identification of multiple genotypes of the salmonid parasite Ceratonova shasta with different virulence levels in Chinook Salmon Oncorhynchus tshawytscha suggests that it is possible to immunize fish against subsequent infection and disease. We hypothesized that exposure of Chinook Salmon to the less-virulent parasite genotype (II) prior to the more virulent parasite genotype (I) would decrease disease and/or result in fewer mature parasites compared with fish only infected with the more virulent genotype. To test this hypothesis, fish were challenged in a combination of field and laboratory exposures, and we measured infection prevalence, percent morbidity, and mature parasite production. Neither mortality nor mature parasite production were reduced when fish were exposed to genotype II prior to genotype I compared with fish exposed only to genotype I, suggesting that protection against C. shasta using a less-virulent genotype of the parasite does not occur.

Received June 9, 2014; accepted September 19, 2014     

Assessment of diclofenac LC50 reference values in juvenile and embryonic stages of the zebrafish (Danio rerio)

The aim of the study was to compare the acute toxicity of diclofenac to juvenile and embryonic stages of the zebrafish (Danio rerio). Acute toxicity tests were performed on the aquarium fish Danio rerio, which is one of the model organisms most commonly used in toxicity testing. The tests were performed using a semi-static method according to OECD guideline No. 203 (Fish, acute toxicity test). Embryo toxicity tests were performed in zebrafish embryos (Danio rerio) in compliance with OECD No. 212 methodology (Fish, short-term toxicity test on embryo and sac-fry stages). The results were subjected to a probit analysis using the EKO-TOX 5.2 programme to determine 96hLC50 and 144hLC50 (median lethal concentration, 50% mortality after a 96 h or 144 h interval, respectively) values of diclofenac. The statistical significance of the difference between LC50 values in juvenile and embryonic stages of Danio rerio was tested using the Mann-Whitney non-parametric test implemented in the Unistat 5.1 programme. The LC50 mean value of diclofenac was 166.6 +/- 9.8 mg/L in juvenile Danio rerio, and 6.11 +/- 2.48 mg/L in embryonic stages of Danio rerio. The study demonstrated a statistically higher sensitivity to diclofenac (P < 0.05) in embryonic stages compared to the juvenile fish.     

The Use of Lufenuron to Treat Fish Lice (Argulus sp) in Koi (Cyprinus carpio)

Fish lice can cause significant morbidity and death in heavily infested fish. In addition to being a mechanical irritant when sucking blood, Argulus sp have been shown to be the vector for other fish diseases. Koi carp from a pond environment were presented with multiple raised dark spots on their dorsa and sides. The primary differential disease diagnosis was an Argulus sp. Parasites removed from the affected fish were examined under a dissection microscope, and the definitive diagnosis was determined to be Argulus sp infestation. Treatment with lufenuron (Program; Novartis, Greensboro, NC USA) was initiated with one 409.8-mg tablet per 1,000 US gallons (3,785 L) of water for a concentration of approximately 0.1 mg/L. This treatment was repeated once per week for 5 weeks. The fish have been monitored for 13 months after the initial treatment, and thus far, there has been no reappearance of Argulus sp within the aquatic environment.     

Preliminary Assessment of the Tolerance and Efficacy of Florfenicol against Edwardsiella ictaluri Administered in Feed to Channel Catfish

Abstract

A tolerance study was conducted to determine the palatability of florfenicol to channel catfish Ictalurus punctatus. Four tanks of fish (20 fish/tank) were assigned to each of five treatments distinguished by the amount of florfenicol given in feed per kilogram of body weight, namely, 0, 10, 20, 40, or 100 mg. Fish were fed at a rate of 2.5% of body weight per day for 10 consecutive days. On day 11, all surviving fish were euthanatized, counted, and weighed as a group. Florfenicol- medicated feed was palatable to fish at doses of 10, 20, 40, and 100 mg for 10 consecutive days. All 400 fish were necropsied and examined by histopathology, and no treatment-related changes were observed. In a separate exploratory efficacy study, four tanks (20 fish/tank) were assigned to each of the following treatments: (1) not challenged with Edwardsiella ictaluri and fed unmedicated feed, (2) challenged with E. ictaluri and fed unmedicated feed, (3) challenged with E. ictaluri and fed florfenicol at 10 mg per kilogram of body weight, (4) challenged and fed florfenicol at 20 mg/kg, and (5) challenged and fed florfenicol at 40 mg/kg. Treatment was initiated the day after inoculation, and feed was administered by hand for five consecutive days at 2.5% of body weight. The cumulative mortality observed over a 17-d period in treatment groups 1–5 was 2.5, 57.5, 0, 1.25, and 1.25%, respectively. All 400 fish were necropsied and examined by histopathology. The results indicate that florfenicol was effective in controlling mortality from enteric septicemia of catfish with no adverse treatment-related tissue changes. Florfenicol was palatable, safe, and efficacious in controlling mortality due to infection by E. ictaluri in channel catfish.     

The Effect of High Total Ammonia Concentration on the Survival of Channel Catfish Experimentally Infected with Flavobacterium columnare

Abstract

Ammonia concentrations in water can affect the severity of Flavobacterium columnare infections in fish. Two trials lasting 7 d each were conducted to determine the effect of a single immersion flush treatment of total ammonia nitrogen (TAN; 15 mg/L) on the survival of channel catfish Ictalurus punctatus infected with F. columnare; the chemical was added while the water flowed continuously through the tanks. Both trials consisted of four treatments: (1) no ammonia exposure and no bacterial challenge (control), (2) ammonia exposure only, (3) bacterial challenge only, and (4) both ammonia exposure and bacterial challenge. Two hours after exposure to ammonia, the highest un-ionized ammonia level was 0.43 mg/L. The percent un-ionized ammonia is based on TAN, temperature, and pH. Caudal fins from three fish in each treatment were sampled at 24 h posttreatment to be analyzed by quantitative real-time polymerase chain reaction (qPCR). No significant difference in survival (mean ± SE) was noted between the channel catfish in treatment 1 (95.2 ± 1.2%) and those in treatment 2 (95.6 ± 1.0%); however, survival in both treatments 1 and 2 differed significantly from that in treatments 3 (8.5 ± 4.5%) and 4 (41.8 ± 12.7%). Treatment 4 catfish had significantly higher survival than treatment 3 catfish. Quantitative PCR data showed that treatment 4 fish had significantly less F. columnare (7.6 × 10⁵) than did treatment 3 fish (1.2 × 10⁷), and treatment 2 fish (8.5 × 10³) had significantly less bacteria than did treatment 1 fish (6.9 × 10⁴), indicating that ammonia limited the F. columnare infection. The highest mean concentration of the bacteria (3.9 × 10⁷) was found on moribund fish. The ammonia concentrations tested did not negatively influence fish survival but interfered with the infection process. An in vitro assay was also conducted to evaluate the direct effects of ammonia on F. columnare.

Received September 15, 2010; accepted May 7, 2011     

Effectiveness of Praziquantel Bath Treatments against Bothriocephalus acheilognathi in Grass Carp

Abstract

Many states ban the importation of fish infected with the Asian tapeworm Bothriocephalus acheilognathi. Treatment with an effective tapeworm parasiticide prior to shipment would allow fish to be imported that might otherwise be rejected. In this study, extended praziquantel bath treatments of infected grass carp Ctenopharyngodon idella were tested to determine their efficacy against Asian tapeworms. Preliminary praziquantel treatments of 0.7 mg/L or more for an exposure period of 24 h at grass carp densities of 69 g/L were effective in eliminating all tapeworms from 22-g fish. When the treatment duration was lowered to 12 h, a praziquantel concentration of 2.8 mg/L was required for effective treatment. In replicated studies, significantly reduced tapeworm numbers (0–5 tapeworms per treated fish compared with 30+ tapeworms per control fish) were observed following 24-h exposures to praziquantel at 0.5, 0.7, 1.0, and 1.5 mg/ L. Tapeworm elimination occurred only at the maximum concentration of 1.5 mg/L when 88-g grass carp were stocked at a density of approximately 6 g/L. When fish density was raised to 60 g/L, the 1.5-mg/L treatment did not eliminate all tapeworms: 4 of 30 fish contained a single tapeworm.     

Effect of Nanophyetus salmincola and Bacterial Co-Infection on Mortality of Juvenile Chinook Salmon

The freshwater trematode Nanophyetus salmincola has been demonstrated to impair salmonid immune function and resistance to the marine pathogen Vibrio anguillarum, potentially resulting in ocean mortality. We examined whether infection by the parasite N. salmincola similarly increases mortality of juvenile Chinook Salmon Oncorhynchus tshawytscha when they are exposed to the freshwater pathogens Flavobacterium columnare or Aeromonas salmonicida, two bacteria that juvenile salmonids might encounter during their migration to the marine environment. We used a two-part experimental design where juvenile Chinook Salmon were first infected with N. salmincola through cohabitation with infected freshwater snails, Juga spp., and then challenged with either F. columnare or A. salmonicida. Cumulative percent mortality from F. columnare infection was higher in N. salmincola-parasitized fish than in nonparasitized fish. In contrast, cumulative percent mortality from A. salmonicida infection did not differ between N. salmincola-parasitized and nonparasitized groups. No mortalities were observed in the N. salmincola-parasitized-only and control groups from either challenge. Our study demonstrates that a relatively high mean intensity (>200 metacercariae per posterior kidney) of encysted N. salmincola metacercariae can alter the outcomes of bacterial infection in juvenile Chinook Salmon, which might have implications for disease in wild fish populations.

Received February 24, 2015; accepted September 7, 2015     

Bacterial Analysis of Fertilized Eggs of Atlantic Salmon from the Penobscot,Naraguagus, and Machias Rivers,Maine

Serious losses have occurred at the U.S. Fish and Wildlife Service, Craig Brook National Fish Hatchery, East Orland, Maine, among eggs that were taken from Atlantic Salmon Salmo salar, which were held as captive broodfish during their returns to the Penobscot River, Naraguagus River, and Machias River to spawn. Bacterial isolations were attempted from external surfaces and the internal contents of individual eggs. Externally and in all cases, Pseudomonas fluorescens was the predominant bacterium associated with the surface of all eggs. These bacteria were resistant to a surface treatment of 1,667 ppm formalin for 15 min and, therefore, the monoclonal nature of P. fluorescens on egg surfaces was considered to result from its ability to resist the germicidal activity of formalin administered for antifungal treatments. Flavobacterium psychrophilum, the cause of bacterial coldwater disease, was isolated from the interior of 23.6, 18.1, and 29.2% of the dead Atlantic Salmon eggs from Penobscot River egg lots A-98, A-100, and A-101, respectively, and concentrations of this pathogen ranged from 1.0 × 10³ to >5 × 10⁸ CFU per gram of dead egg. Flavobacterium psychrophilum was also isolated from 8.3, 26.7, and 10.0% of the dead eggs from Naraguagus River egg lots N-158, N-161, and N-163, respectively, in which concentrations of this organism ranged from 1.0 × 10³ to 7.5 × 10⁸ CFU per gram of egg. This bacterium was also isolated from within 18.3% and 3.3% of the dead eggs from Machias River egg lots M-128 and M-142, respectively, and its concentrations ranged from 1.0 × 10³ to 1.5 × 10⁸ CFU per gram of egg. The finding of F. psychrophilum from within these eggs is indicative of this pathogen's widespread and persistent prevalence in Atlantic Salmon in New England.

Received December 19, 2014; accepted May 4, 2015     

Characterization and Inhibition of Nitrite Uptake in Shortnose Sturgeon Fingerlings

Abstract

Efforts are underway to culture the endangered shortnose sturgeon Acipenser brevirostrum for possible reintroduction. As part of a larger project to develop culture techniques for this species, the uptake of nitrite was evaluated in fingerlings (16.5 ± 4.85 g; mean ± SD). Plasma nitrite concentrations increased significantly with exposure time (0–5 d) and dose (0–4 mg nitrite-N/L). Shortnose sturgeon fingerlings were able to concentrate nitrite in their plasma to more than 63 times the environmental concentration. Chloride, as either sodium chloride or calcium chloride, partially inhibited nitrite uptake. However, calcium chloride was a better inhibitor. After previous exposure (2 d at 2.13 ± 0.080 mg nitrite-N/L) plasma nitrite-N decreased from 165.5 to 36.7 mg/L during a 3-d simultaneous exposure to 2.13 ± 0.080 mg nitrite-N/L and treatment with 40 mg chloride/L as calcium chloride. The addition of calcium chloride to the water appeared to be an effective means of preventing nitrite uptake and treating nitrite toxicity in hatchery-reared shortnose sturgeon fingerlings.     

Replacing fish oil and astaxanthin by microalgal sources produced different metabolic responses in juvenile rainbow trout fed 2 types of practical diets

Dietary fish oil supplementation provides n-3 long-chained polyunsaturated fatty acids for supporting fish growth and metabolism and enriching fillet with eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; c22:6n-3). Two experiments were performed as a 3 × 2 factorial arrangement of dietary treatments for 16 wk to determine effects and mechanisms of replacing 0%, 50%, and 100% fish oil with DHA-rich microalgae in combination with synthetic vs. microalgal source of astaxanthin in plant protein meal (PM)- or fishmeal (FM)- based diets for juvenile rainbow trout (Oncorhynchus mykiss). Fish (22 ± 0.26 g) were stocked at 17/tank and 3 tanks/diet. The 100% fish oil replacement impaired (P < 0.0001) growth performance, dietary protein and energy utilization, body indices, and tissue accumulation of DHA and EPA in both diet series. The impairments were associated (P < 0.05) with upregulation of hepatic gene expression related to growth (ghr1and igf1) and biosynthesis of DHA and EPA (fads6 and evol5) that was more dramatic in the FM than PM diet-fed fish, and more pronounced on tissue EPA than DHA concentrations. The source of astaxanthin exerted interaction effects with the fish oil replacement on several measures including muscle total cholesterol concentrations. In conclusion, replacing fish oil by the DHA-rich microalgae produced more negative metabolic responses than the substitution of synthetic astaxanthin by the microalgal source in juvenile rainbow trout fed 2 types of practical diets.     

Blood chemistry values of juvenile red pacu (Piaractus brachypomus)

Abstract: Blood samples were collected from 29 juvenile red pacu ( Piaractus brachypomus ), ornamental freshwater fish, to establish baseline blood chemistry values. Mean (minimum-maximum) values, obtained by automated bichromatic analysis and ion selective electrode analysis, were as follows: sodium, 150.4 (146–159) mmol/L; potassium, 3.93 (2.7–5.0) mmol/L; chloride, 138.7 (128–150) mmol/L; total CO₂, 7.5 (6–10) mmol/L; albumin, 0.86 (0.5–1.0) g/dL; lactate dehydrogenase, 237.8 (65–692) IU/L; aspartate aminotransferase, 49.1 (0–125) IU/L; creatinine, 0.31 (0.2–0.4) mg/dL; calcium, 10.80 (9.5–12.5) mg/dL; anion gap, 6.89 (1.2–12.5) mmol/L; and phosphorus, 7.29 (4.1–8.9) mg/dL.     

Comparative single‐dose pharmacokinetics of orally administered florfenicol in rainbow trout (Oncorhynchus mykiss,Walbaum, 1792) at health and experimental infection with Streptococcus iniae or Lactococcus garvieae

This study evaluates changes in the pharmacokinetic behavior of a single oral dose of florfenicol in rainbow trouts experimentally infected with Lactococcus garvieae or Streptococcus iniae. One hundred and fifty fish were randomly divided into three equal groups: 1—healthy fish, 2—fish inoculated with S. iniae (2.87 × 10⁷ CFU/ml, i.p.), and 3—fish inoculated with L. garvieae (6.8 × 10⁵ CFU/ml, i.p.). Florfenicol was administered to all groups at 15 mg/kg by oral gavage. Blood sampling was performed at 0, 2, 3, 6, 8, 12, 24, 48, 72, and 120 hr after drug administration to each group, and plasma concentration of florfenicol was assayed by HPLC method. The MICs of florfenicol were 1.2 μg/ml and 5 μg/ml against L. garviae and S. iniae, respectively. Healthy fish showed higher values for most of the PK/PD parameters as compared to fish infected with L. garvieae which was reversed in fish infected with S. iniae. Fish infected with L. garvieae showed decreased relative bioavailability accompanied by increased volume of distribution at steady‐state (Vd_ss) and total body clearance (Cl_B)_. Infection with S. iniae increased the peak concentration of drug after administration (Cmax) and decreased elimination half‐life (T_{1/2 β})_, central compartment volume (V_c), and Vd_ss. In conclusion, infection with these bacteria can affect the pharmacokinetic behavior of florfenicol in rainbow trouts as shown by decreased bioavailability and increased total body clearance and volume of distribution in L. garvieae infection and decreased volume of distribution accompanied by increased Cmax in S. iniae‐infected fish.