Rick J. Cordes

Observations on Hydrogen Peroxide Control of Saprolegnia spp. during Rainbow Trout Egg Incubation

Abstract Daily treatments of 250, 500, and 1,000 mg hydrogen peroxide/L for 15 min were evaluated for fungal control on incubating eggs from two strains of rainbow trout Oncorhynchus mykiss. Observed infection rates and egg clumping were extensive enough in incubator trays receiving treatments of 250 or 500 mg hydrogen peroxide/L to make egg and fry handling difficult. The 1,000 mg/L treatment provided fungal control similar to daily formalin treatments of 1,667 mg/L for 15 min. Despite the differences in infection rates and clumping, egg survival was not affected by any of the treatments used.

Reproductive Performance of Inland Fall Chinook Salmon

Abstract Reproductive performance data were collected for inland fall chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, in 1988 and 1998. This population exists outside the native geographical range of chinook salmon and completes its entire life cycle in freshwater. Female weights and lengths, total fecundity, relative fecundity (eggs/mm), egg size, and egg survival were all considerably less than reported for anadromous chinook salmon stocks in their native range. Mean weight of spawning females was 2.73 kg in 1988 and 2.01 kg in 1998. Total fecundity was not significantly different at 2,892 eggs in 1988 and 2,496 eggs in 1998. Egg survival to the eyed stage averaged 37.7% in 1988 and 43.8% in 1998 and ranged from 0% to 96%. Relative fecundity (eggs/kg), egg size, and egg survival to the eyed stage were similar for each year. Relative fecundity (eggs/mm of total length) declined from 1988 to 1998. Total fecundity was linearly related to fish length in 1998 and in both years combined....

Use of Formalin during Incubation of Eyed Eggs of Inland Fall Chinook Salmon

Abstract The influence of daily formalin treatments on eyed egg and fry mortality was evaluated during the incubation of eyed eggs of inland fall chinook salmon Oncorhynchus tshawytscha. A 3–5% increase in survival was observed in trays of eggs treated with formalin at 1,667 mg/L for 15 min daily from egg eye-up until just before hatch compared with incubation trays from which dead eggs were manually removed to control Saprolegnia. Egg survival in trays receiving both daily formalin treatments and manual egg removal did not differ significantly from those trays receiving only formalin treatments. Significant reductions in mortality were observed prehatch when formalin was used, and there was no difference in mortality from hatch to fry swim-up. Both formalin treatments and the hand-picking of dead eggs adequately controlled visible fungal development from egg eye-up to hatching.

Bacterial Numbers from Landlocked Fall Chinook Salmon Eyed Eggs Subjected to Various Formalin Treatments as Determined by Scanning Electron Microscopy and Bacteriological Culture Methods

Abstract This study compared two methods of enumerating bacteria adhered to the external membrane of eggs of landlocked fall Chinook salmon Oncorhynchus tshawytscha that were subjected to different formalin treatment regimes from egg eye-up to fry hatch. Bacterial numbers were recorded by either directly counting bacteria via a scanning electron microscope (SEM) or via established bacterial culture methods that provided the number of colony-forming units. Treatment regimes consisted of a daily 15-min exposure to formalin at either 500 mg/L or 1,667 mg/ L or no formalin initially followed by exposure to a 1,667-mg/L dose starting 7 d after eye-up. A control group did not receive any formalin treatments throughout the experiment. No significant correlation was observed between the number of colony-forming units (CFUs) per square millimeter of egg membrane determined by plate culture and the number of bacteria per square millimeter counted with the SEM. Bacterial numbers determined by the SEM were 40–120 tim...

Bacterial Populations during Inland Fall Chinook Salmon Egg Culture in Vertical-Flow Tray Incubators

Abstract Bacterial samples were collected from water flowing through vertically stacked trays during the incubation of eggs of inland fall chinook salmon Oncorhynchus tshawytscha. Bacteria numbers gradually increased until the eyed stage of egg development and then decreased after removal of dead eggs. Bacterial abundance peaked during hatching and declined thereafter. Throughout incubation, bacterial abundance increased from the top to the bottom of the stack. Mechanical picking of dead eggs at the eyed stage led to a decrease in bacteria numbers. Removal of dead eggs and fry by hand picking resulted in a temporary increase in bacteria population, with a return to prepicking levels after 30 min. Egg survival at the eyed stage of development was inversely related to tray position, decreasing from top to bottom of the incubation stack. Survival from the eyed stage to fry swim-up was not affected by tray location. If high egg mortality is anticipated, hatchery managers may want to consider changes in egg re...

Use of Formalin during Incubation of Rainbow Trout Eyed Eggs

Abstract The influence of daily formalin treatments on eyed egg and fry mortality was evaluated during the incubation of eyed eggs of Cleghorn strain rainbow trout Oncorhynchus mykiss in vertical-flow incubators. The study was initiated in 1995 and replicated yearly through 1998. In 1997 and 1998, significant (P < 0.05) increases in survival were observed in trays of eggs treated with formalin at 1,667 mg/L for 15 min daily from egg eye-up until just before hatch compared with incubation trays where dead eggs were manually removed for control of Saprolegnia sp. In 1996, 1997, and 1998, significant mortality reductions were observed prehatch when using formalin. A significant improvement in survival from hatch to fry swim-up occurred only in 1998. No significant differences in survival occurred during any life stage in 1995. Yearly differences in formalin influences are attributed to changes in the age of broodfish, spawning frequency, and sample sizes. Both formalin treatments and hand picking of dead egg...

Soft-Egg Disease in Landlocked Fall Chinook Salmon Eggs: Possible Causes and Therapeutic Treatments

Abstract Soft-egg disease was observed in the spawn from 5 of 15 landlocked fall chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, with the percentage of prematurely hatching fry per spawn ranging up to 42.0%. Soft-egg disease was only identified in eggs collected from presumed 4-year-old salmon, and its occurrence is hypothesized to be at least partially caused by maternal dietary stress during egg development. Egg mortality after the appearance of soft-egg symptoms was significantly less in the incubation trays receiving daily hydrogen peroxide treatments at 1,000 or 2,000 mg/L for 15 min and trays receiving either daily or twice-daily formalin treatments at 1,667 mg/L for 15 min, compared with the trays that received either iodophor treatments or no therapeutic treatment at all.

Bacterial Populations during Rainbow Trout Egg Culture in Vertical-Flow Tray Incubators

Abstract Bacterial samples were collected from water flowing through vertically stacked trays during incubation of eggs of rainbow trout Oncorhynchus mykiss. An initial peak in bacteria numbers occurred at the eyed egg stage with a subsequent decline after mechanical picking of dead eggs. A second peak, greater in magnitude and duration than the first, began at hatching and lasted for approximately 10 d before decreasing. A final peak was observed just before fry removal from the incubators at swim-up. Throughout incubation, bacterial abundance increased from top to bottom of each incubator stack. Mechanical picking of dead eggs at the eyed stage led to decreased bacteria numbers. Egg survival at the eyed stage and survival to fry swim-up were not influenced by tray position.

BAFFLE USAGE IN COVERED RACEWAYS

Abstract Baffle usage was examined during culture of rainbow trout Oncorhynchus mykiss in covered raceways at McNenny State Fish Hatchery, Spearfish, South Dakota. Baffles had no noticeable impact on fish growth, feed conversion, or mortality. However, rainbow trout reared in baffled raceways had greater pectoral and pelvic fin erosion than fish raised in unbaffled systems. Dorsal fins, though apparently unaffected by baffles, decreased in proportionate length after just 46 d of rearing. Outflows of total suspended solids were similar in baffled and unbaffled raceways. Baffles are effective tools to move fish waste, maintain raceway cleanliness, and help hatcheries meet pollutant outflow regulations. However, the decrease in fish quality, as measured by fin erosion, should be considered before baffles are used.

Use of Formalin Treatments During Incubation of Eyed Eggs of Brown Trout

Abstract To test the efficacy of formalin in controlling the fungus Saprolegnia, we administered daily formalin treatments (1,667 mg/L for 15 min) to embryos (eyed eggs to hatch) of brown trout Salmo trutta and compared their survival with that of untreated embryos. The study was conducted each year from 1996 to 1998. In all 3 years, embryo survival to hatch in both groups was greater than 90%. Survival to hatch was not significantly improved in the treated trays of eggs compared with the untreated trays, where dead eggs were manually removed for Saprolegnia control. Both formalin treatments and hand-picking of dead eggs adequately controlled visible fungal development. Although not essential for fungal control, formalin treatments on high-quality brown trout eggs from the eyed stage of embryo development through hatch are recommended to provide reductions in hatchery labor, but only if they can be administered safely.