Diel microhabitat use of age-0 bull trout in Indian Creek, Washington

Abstract – We studied diel microhabitat use at the focal point of age‐0 bull trout, Salvelinus confluentus, in Indian Creek, Washington during mid‐summer and fall of 1997. Microhabitat variables included water depth and velocity, distance from the stream bottom, habitat and refuge use, substrate type, and substrate embeddedness. Age‐0 fish were located over fines and gravel substrates in shallow, low‐velocity water near stream margins, but were located in shallower water at night. Bull trout were highly associated with loose substrate, and used the substrate interstices for refuge cover. Diurnal bull trout counts decreased and no age‐0 fish were observed after 15 September at water temperatures below 6.1 °C. Nocturnal counts remained relatively constant throughout the study. Our results suggest that age‐0 bull trout surveys be conducted at night when summer water temperatures begin to decline.     

花羔红点鲑人工繁殖和仔鱼培育技术研究

对花羔红点鲑人工繁殖和仔鱼培育技术进步了研究，并探讨了亲鱼大小与绝对繁殖力、受精卵发育时间与温度、成熟卵大小与初次摄食仔鱼大小等问题以及人工养殖群体对野生种群的影响。     

Muscle carotenoid concentrations in sexually maturing and immature Arctic charr, Salvelinus alpinus (L.)

Muscle carotenoid concentrations were measured in immature and maturing 2+ Arctic charr, Salvelinus alpinus (L.), sampled from April until ovulation started in November. In immature fish, muscle carotenoid concentration increased steadily and had reached about 10 mg kg^?1 by the end of the experiment. In mature fish of both sexes, pigment concentrations decreased during the autumn and muscle carotenoid concentrations were significantly lower than in the immature fish during the latter stages of the trial. No significant difference in muscle pigmentation was observed between sexes. Carotenoid concentrations were lowest in the cranial region of the fillet, but decreased in all parts of the fillet when the charr became mature. In females, the decrease seemed to be most marked in the caudal region. At the termination of the experiment, fillets accounted for about one-half of the carotenoid content in mature fish of both sexes. High concentrations of pigment were recorded in the skin and fins of mature males. In mature female charr, pigment was almost equally distributed among skin, fins and ovaries     

Importance of fatty acids in broodstock diets with emphasis on Arctic char (Salvelinus alpinus) eggs

The importance of long-chain polyunsaturated fatty acids, especially the eicosanoid precursors, is addressed in this paper. It has been generally recognized that eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) are of significant importance in fish reproduction while arachidonic acid (AA, 20:4n-6) has often been overlooked. The ratio between C20 fatty acids EPA and AA might be important for many physiological functions depending on the species evolution and its requirements. Arctic char (Salvelinus alpinus) has a much more pronounced freshwater history and therefore different fatty acid requirements than the other commonly farmed salmonids such as salmon (Salmo salar), brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). Therefore there is reason to formulate a feed that is more suitable for farming of this freshwater species. In this study, freshwater wild-origin char eggs were compared to farmed eggs of char. The ratio n-3/n-6 of total phospholipids of eggs was much lower in the wild fish, 3.5 versus 13.5, and the hatching rate of eggs from natural environment was much higher (20–70% vs. >80%). We conclude that feed based on marine raw product does not fulfill the requirements for essential fatty acids for freshwater char and we suggest that AA is supplemented to the broodstock diet and that at least linoleic acid (18:2n-6) is included in the on-growth diet formulas to lower the n-3/n-6 fatty acid ratio.     

Feed intake and growth of Arctic charr, Salvelinus alpinus (L.), fed diets supplemented with oxytetracycline and squid extract

This study examined the long-term effects of a potential feeding deterrent, oxytetracycline (OTC), and a putative feeding stimulant, squid extract, on feed intake, growth and dry matter (DM) digestibility in Arctic charr, Salvelinus alpinus (L.). Fish were fed one of four diets for 9 weeks: 1. commercial feed formulation (basic); 2. BM (basic plus 20 g kg⁻¹ OTC); 3. BMS (BM plus 10 g kg⁻¹ squid extract); 4. BS (basic plus 10 g kg⁻¹ squid extract). The feed intake of Arctic charr was not reduced by the addition of OTC to the basic feed, and addition of squid extract to the medicated feed did not enhance feed consumption. DM digestibility and growth tended to be reduced in groups of fish fed diets supplemented with the antibiotic (BM and BMS). This suggests that OTC may have interfered with nutrient digestion and absorption. OTC does not seem to be a feeding deterrent for Arctic charr, possibly indicating that the charr is a rather unselective feeder. Because the medicated feeds were readily accepted, there may be little to be gained by addition of feeding stimulants to these types of feeds for charr.     

Effect of androgens on seawater adaptation in Arctic char,Salvelinus alpinus

Sexually immature two-year old Arctic char (Salvelinus alpinus) were implanted with Silastic capsules containing testosterone or 11-ketoandrostenedione in early spring. Seawater adaptability of the hormone-treated and sham-operated fish was tested periodically from May to August using a 48h seawater challenge test with 25‰ seawater. The sham-operated control fish displayed a seasonal pattern in seawater adaptation, showing a good hypoosmoregulatory ability until mid June followed by a marked increase in plasma sodium and magnesium levels in July and August. Gill Na⁺-K⁺-ATPase activity decreased concurrently with the observed decrease in seawater adaptability. Over the same period the androgen-treated fish displayed a similar pattern in seawater adaptability, however, in May and June the plasma sodium levels were significantly higher in both androgen-treated groups compared to the control group. Plasma magnesium regulation was impaired in both androgen-treated groups in August. Gill Na⁺-K⁺-ATPase activity in the testosterone-treated fish was lower in June compared to the control fish, whereas the activity was not affected by 11-ketoandrostenedione treatment. The results show that while androgens impair the hypoosmoregulatory capacity in Arctic char, the seasonal pattern of seawater adaptability is not affected.     

Factors affecting habitat selection by a small spawning charr population, bull trout, Salvelinus confluentus: implications for recovery of an endangered species

Bull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ‘to ensure the long‐term persistence of self‐sustaining bull trout populations’. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization.     

白斑红点鲑精子形态和超微结构的研究

应用扫描和透射电镜观察了白斑红点鲑(Salvelinus leucomaenis)精子的形态和超微结构。白斑红点鲑精子由头部、中段和尾部组成。头部呈椭球形,主要结构是细胞核,核前端无顶体,后端有植入窝,植入窝较深,凹入细胞核的1/3,核中染色质致密,存在着不规则的网络状间隙;中段包括中心粒复合体和袖套,中心粒复合体主要由近端中心粒和远端中心粒组成,近端中心粒为典型的9组三联微管结构,与远端中心粒相互垂直,远端中心粒向下延伸形成轴丝。袖套与细胞核后端相连,含有丰富的线粒体和囊泡,部分线粒体彼此融合,形成复合线粒体,囊泡有两种;白斑红点鲑精子尾部细长,主要结构是轴丝,为典型的9+2微管结构,轴丝被许多囊泡包围,质膜向外突出形成上下对称,但大小不同的两个侧鳍。