Freshwater Juveniles Research Articles

Identification of Hatchery and Naturally Spawning Stocks of Columbia Basin Spring Chinook Salmon by Scale Pattern Analyses

Abstract Scale pattern analysis (SPA) was used to differentiate hatchery and natural-origin stocks of spring-run chinook salmon Oncorhynchus tshawytscha of age 1.2 (= age 4; spent one winter as juveniles in fresh water and two winters in the ocean; one winter of egg incubation is implied) from the Snake, Wenatchee, and Deschutes subbasins of the Columbia River basin. Linear discriminant analyses indicated that hatchery and natural-origin stocks within each subbasin could be identified with a relatively high degree of accuracy. High classification accuracies were also obtained by comparing pooled hatchery stocks from the three Columbia River subbasins with pooled natural-origin stocks from those same subbasins. For a composite mixed-stock analysis, samples of unknown origin were obtained from Bonneville Dam, a site on the lower Columbia River where a mixed population of spring chinook salmon stocks is found. This analysis, which was done with a classification model based on pooled hatchery and natural-orig...

Influence of size, winter duration and density on sexual maturation of Atlantic salmon (Salmo salar) juveniles in Little Codroy River (southwest Newfoundland)

Factors affecting sexual maturation of Atlantic salmon (Salmo salar L.) juveniles in fresh water were analysed under wild conditions in Little Codroy River (southwest Newfoundland). Large size after the first year of life and short winters favoured maturation of age 1 + male parr. Incidence of maturing 1+ males was greater where high densities of parr (>0.2 individuals m 2; fish >6cm fork length) were recorded in the second season of growth. These results were discussed according to current knowledge on early maturation in Atlantic salmon.

Acute nitrite toxicity and methemoglobinemia in juvenile milkfish ( Chanos chanos Forsskal)

Nitrite was about 55 times more toxic to milkfish juveniles in fresh water than in 16% brackish water: the 48-h median lethal concentrations were 12 mg NO 2N/l (95% confidence limit=7.4–19.6) and 675 mg NO 2N/l (95% confidence limit = 435.8–1,045.4) respectively. Methemoglobin levels were higher for a given concentration of nitrite in milkfish kept in fresh water than in the brackish water. Methemoglobin decreased to a normal level within 24–26 hours of the removal of nitrite.

Sensitivity of Alaskan Freshwater and Anadromous Fishes to Prudhoe Bay Crude Oil and Benzene

The sensitivity of various species and life stages of Alaskan freshwater and anadromous fishes to benzene and the water-soluble fraction of Prudhoe Bay crude oil was determined with 96-hour toxicity tests. Freshwater juveniles of the six salmonid species tested had similar sensitivities. Median tolerance limits (TLmˈs) of these salmonids for crude oil ranged from 2.7 to 4.4 mg/liter; TLmˈs of benzene ranged from 11.7 to 14.7 μl/liter. Threespine sticklebacks and, to a lesser extent, slimy sculpins were more tolerant than salmonids and had larger TLmˈs: Threespine sticklebacks had a crude-oil TLm of 10.4 mg/liter and a benzene TLm of 24.8 μl/liter; slimy sculpins had a crude-oil TLm of 6.44 mg/liter and a benzene TLm of 15.4 μl/liter. Eggs of pink salmon and coho salmon were quite tolerant to crude oil (TLm > 12 mg/liter) and benzene (TLm = 339–542 μl/liter). Emergent fry were the most sensitive freshwater stage (crude-oil TLm = 8.0 mg/liter; benzene TLm = 12.3–17.1 μl/liter). Out-migrant salmonids tested in seawater were twice as sensitive as out-migrant salmonids tested in fresh water, apparently because of the additional stress of entering seawater and the physiological changes associated with this transition. Freshwater TLmˈs were 2.3–8.0 mg/liter for crude oil and 10.8–17.1 μl/liter for benzene. Corresponding seawater sensitivities were 1.1–3.6 mg/liter for crude oil and 5.5–8.5 μl/liter for benzene.

Potassium, sodium, magnesium and calcium contents of Chinook salmon tissues during various stages of the life cycle

1. 1. The potassium, sodium, magnesium and calcium contents of plasma, red cells, brain, heart, muscle, liver, kidney and gills have been measured in Chinook salmon ( Oncorhynchus tshawytscha) during four stages of the life cycle: (1) while juveniles in fresh water, (2) after 2 weeks in seawater, (3) as mature adults in the ocean, and (4) after 3–4 months of fasting at the spawning grounds. 2. 2. Although plasma cation concentrations changed with each alteration in ionic environment, a remarkable constancy of cellular cation composition is maintained except for the juveniles in seawater. 3. 3. The normal potassium/nitrogen ratio in the muscle of spawning salmon is inconsistent with the hypothesis that pathological hyperadrenocorticism occurs at this stage.