Behavioral interactions between coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus shawytscha) and prey fish species

Abstract— The predator-prey behavioral interactions between two salmon species, coho salmon ( Oncorhynchus kisutch ) and chinook salmon ( Oncorhynchus tshawytscha ), and their prey species were examined under laboratory conditions. These behaviors were studied to determine the bases for prey selection by salmon in Lake Michigan and ultimately facilitate predictions on shifts or changes in salmon diets. Chinook and coho salmon captured all prey items in the open water portion of the aquarium, and they had similar attack behaviors. Average attack swimming speeds varied from 2.6 to 3.6 m/s, and average escape swimming speeds varied from 2.6 to 2.9 m/s. There were no significant differences in attack swimming speeds and escape swimming speeds. There was a significant difference in median reactive distances between the prey captured and those that escaped. There was no reactive distance (0.00 m) for 96% and 98% of the successfully captured prey by chinook and coho salmon, respectively. Only 4% and 10% of the unsuccessful attacks by chinook and coho salmon, respectively, had no reactive distance (0.00 m). Salmon would repeatedly attack a school and capture individuals separated from the school. Alewives, bloaters and fathead minnows were easy prey because they remained in the open water portion of the aquarium and stayed in schools until only a few individuals remained. The schooling behavior of spottail shiners and emerald shiners was an effective anti-predation tactic against salmon attacks. After some experience with yellow perch, salmon were reluctant to attack them and would often break off attacks on them. When coho salmon were presented with different proportions of bloaters and yellow perch, they significantly attacked and captured bloaters in preference to yellow perch.     

Survival of smaller sport caught chinook, Oncorhynchus tshawytscha (Walbaum), and coho, Oncorhynchus kisutch (Walbaum), salmon from Lake Michigan and its management implications

Abstract The survival of small-sized (<50.8 cm) chinook salmon, Oncorhynchus tshawytscha (Walbaum), and coho salmon, Oncorhynchus kitsutch (Walbaum), caught by sport fishing was determined to assess the potential for increasing the size limit for these fish. Fishermen were recently catching smaller salmon than in the 1970s, but salmon growth rates had not changed. To be an effective management option, the survival rate of hooked and returned fish must be high. The overall survival rates were high: 76% for chinook salmon and 70% for coho salmon. There was no significant difference in survival of the coho salmon with size of hook used ( P = 0.31). Any mortality among fish was generally acute; fish hooked deep in the mouth or gills generally bled and died shortly after capture. Fish hooked in the gills had a significantly greater mortality ( P = 0.0002). The overall high survival rate for these species was the result of a small proportion of fish being hooked in the gills or deep in the mouth. Since the survival rate of the salmon was high, the size limit could be increased to allow smaller fish to grow to sizes preferred by sport fishermen.     

Possibility of anisakid larvae infection in farmed salmon

SUMMARY: Nematodes belonging to the family Anisakidae including Anisakis simplex and Pseudoterranova decipiens are known to cause anisakiasis when their live larvae are ingested by humans. We estimated the possibility of anisakid infection to salmonids, farmed in sea net-pens at Onagawa Bay, Miyagi, Japan, in 1992, 1998 and 1999, by direct examination of the edible muscle and examination of the contents of the alimentary canal. From direct examination of the muscle, no nematode was found in the 249 farmed coho salmon Oncorhynchus kisutch and 40 farmed rainbow trout Oncorhynchus mykiss . In contrast, third-stage larvae of Anisakis simplex were found in seven of 14 wild coho salmon caught in Russia and all the 40 wild chum salmon Oncorhynchus keta caught at Nemuro and Kesennuma in 1998. The stomach and intestines of 521 farmed coho salmon and 40 farmed rainbow trout were examined carefully for the existence of possible carrier organisms such as crustaceans, fish or squid. Such carrier organisms were not found in the stomach and intestines of farmed fish. Thus, we conclude that the possibility of anisakid infection is very low in farmed salmonids.     

Estimates of genetic and phenotypic parameters for length and weight of marine net-pen reared coho salmon (Oncorhynchus kisutch Walbaum)

Heritabilities and genetic and phenotypic correlations were estimated for length and weight of two brood years (BY 1977 and BY 1978) of coho salmon [Oncorhynchus kisutch (Walbaum)] during the marine net-pen phase of rearing. The estimates were calculated from length and weight measurements on progeny resulting from a nested mating design and measurements at approximately 4 and 7 months after entering sea water. Point estimate for heritabilities based on the sire component for BY 1977 were low to moderate (0.02–0.19) and did not differ significantly from zero. On the other hand, BY 1978 estimates ranged from 0.31 to 0.62 and, with two exceptions, were significantly different from zero. The latter estimates may have been inflated by inclusion of variances from non-additive sources, but still indicated that differences in the genetic potential for increased growth between the two year classes may be substantial. Genetic correlations between length and weight within sampling periods were consistently high (0.95–1.00), indicating that pleiotropic gene action or close linkage among genes affects length and weight. Genetic correlations between body size traits (length and weight) between sampling periods varied considerably but suggested a potential for indirect selection gains. Genetic correlation approximations derived using family means or ranks appeared to provide reliable estimates and may be useful when environmental influences cause a significant deviation from normality.     

Dosage-dependent differences in the effect of aromatizable and nonaromatizable androgens on the resulting phenotype of coho salmon (Oncorhynchus kisutch)

This study was conducted to investigate whether aromatization to estrogen could be the cause for the paradoxical feminization of gonads of sexually-undifferentiated fish after treatment with androgen at either high doses or for long periods. The aromatizable androgen 17-methyltestosterone (MT) and the nonaromatizable androgen 17-methyldihydrotestosterone (MDHT) were administered to groups of newly hatched coho salmon (Oncorhynchus kisutch) in a single 2h immersion at concentrations ranging from 6.25 to 6,400µg/l. The effects of treatment were evaluated by determining the resultant proportion of males in each experimental group. The effects of steroid administration on the final mean weight, length and condition factor were also determined. An increase in all these three variables was observed in the groups treated with the higher doses of MT. Regarding the resultant sexual phenotype, the response to both androgens was similar at the majority of doses tested. However, at the highest dose, the proportion of females increased with respect to that of males for MT, but not for MDHT. Since the major difference between the two androgens tested is their capacity to be aromatized, it seems that aromatization to estrogen, rather than inhibition of the biosynthesis of endogenous androgen, may explain the paradoxical feminization encountered.     

Homing behaviour of juvenile coho salmon (Oncorhynchus kisutch) within an off-channel habitat

Abstract – Although homing behaviour has been observed in juvenile Atlantic salmon, brown trout and resident cutthroat trout, this behaviour has not been well studied in juvenile Pacific salmon. We examined the site fidelity and homing behaviour of juvenile coho salmon ( Oncorhynchus kisutch ) by marking and relocating them within an off-channel habitat. Over 80% of displaced fish returned to the area from which they were originally collected. The proportion of fish that returned to the original location did not vary significantly among three sampling dates. However, we found that this proportion decreased over time in a brackish lagoon when we statistically analysed the data reported by Day (1966) . Our results suggest that juvenile coho salmon exhibit strong site fidelity and are able to return to their home ranges after displacement. These behaviours are likely to be important for the winter survival of juvenile coho salmon.     

Effect of thyroid-stimulating hormone on the physiology and morphology of the thyroid gland in coho salmon,Oncorhynchus kisutch

Activity of the thyroid gland of the coho salmon,Oncorhynchus kisutch, was assessed by physiological, histological and ultrastructural criteria after treatment with graded doses of bovine thyrotropin (bTSH) in January and March. Average plasma thyroxine (T₄) levels increased from about 0.8 ng/ml in saline-injected controls to about 15 ng/ml in fish treated with four intraperitoneal injections of 0.8 lU bTSH. Light-microscope observations of one m-thick sections stained with methylene blue and azure II, showed that bTSH treatment increased epithelial height in both presmolts and smolts. Ultrastructural manifestations of increased activity owing to bTSH treatment were also seen, along with evidence of follicle proliferation. Cytoplasmic organelles and secretory granules increased in numbers with increased dosage of bTSH.     

银鲑(oncorhynchus kisutch)形态性状测量

通过对银鲑的形性状测量 ,初步进行了银鲑的种质研究。结果表明银鲑的形态性状如下 :全长 /体长为 1 1 2± 0 0 2 ,头长 /眼径为 4 46± 0 45 ,体长 /体高为 4 49± 0 32 ,尾柄长 /尾柄高为 2 2 9± 0 30 ,体长 /头长为 4 0 4± 0 2 1 ,体长 /叉长为 0 94± 0 0 3 ,头长/头高为 1 2 8± 0 0 8,体长 /尾柄长为 5 2 3± 0 30 ,头长 /吻长为 3 33± 0 2 7,头长 /眼间距为 2 68± 0 2 0 ,背鳍 1 0～ 1 3 ,腹鳍 1 0～ 1 1 ,胸鳍 1 3～ 1 6 ,臀鳍 1 2～ 1 7,侧线鳞 1 2 1～1 4 4 ,幽门盲囊 45～ 83 ,鳃耙 1 9～ 2 3,脊椎骨 58～ 66。     

Sex-specific growth pattern during early life history in masu salmon, Oncorhynchus masou

Abstract –  To examine whether or not sex-specific growth occurs in fry of masu salmon Oncorhynchus masou , 90 half-sibling fry chosen from three different classes of egg size (small, medium and large) and emergence time (period from fertilisation to first feeding; early, middle and late) were raised in a tank for 60 days. In all four replications, male fry grew faster than females. The difference in growth between sexes was greater among siblings hatched from larger eggs. Fast-growing, young male masu salmon show a precocious form that tends to mature without migrating to sea. Slower growing males tend to show the anadromous form, which is only shown in females. Sex-specific life histories may influence the sex-specific growth patterns during early life history.