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A 1.5-acre barrier net, used to enclose large numbers of juvenile Pacific salmon ( Oncorhynchus spp.) for rearing in backwaters along the Columbia River, USA, is described. This type of enclosure may provide additional rearing options to fishery managers.
Six paired lots of yearling lake trout ( Salvelinus namaycush ) reared at densities of 41,000 and 51,000 fish per raceway during their last 9 months in the hatchery were stocked in Lake Ontario. Poststocking survival of the high-density (HD) and low-density (LD) fish was not different for the 1982 year-class. However, for the 1983 year-class, mean survival was significantly different between HD and LD fish ( P < 0.01). Mean survival of HD fish was only 76% that of LD fish ( P < 0.01), and most of the mortality attributable to rearing conditions had apparently occurred within 2 months after stocking. Mean size at stocking was not different for HD and LD fish of the 1982 year-class, but for the 1983 year-class, the LD fish were 6% longer and 22% heavier than the HD fish. Mean lengths and weights of LD and HD fish were not different in samples collected in Lake Ontario at age 2 and older. Size at stocking was not likely the factor that caused the difference in survival. Rather, the rearing conditions (probably water exchange rate in relation to number of fish in the raceway) that resulted in slower growth of the HD fish of the 1983 year-class also caused them to be poorer physiologically than the LD fish. The number of yearling lake trout per rearing unit that will result in maximum contribution to populations in the Great Lakes after stocking may be lower than the rearing densities customarily used at some hatcheries.
Benzocaine is a promising candidate for registration with the U.S. Food and Drug Administration for use as an anesthetic in fish culture, management, and research. A method for the removal of benzocaine from hatchery effluents could speed registration of this drug by eliminating requirements for data on its residues, tolerances, detoxification, and environmental hazards. Carbon filtration effectively removes many organic compounds from water. This study tested the effectiveness of three types of activated carbon for removing benzocaine from water by column filtration under controlled laboratory conditions. An adsorptive capacity was calculated for each type of activated carbon. Filtrasorb 400 (12 × 40 mesh; U.S. standard sieve series) showed the greatest capacity for benzocaine adsorption (76.12 mg benzocaine/g carbon); Filtrasorb 300 (8 × 30 mesh) ranked next (31.93 mg/g); and Filtrasorb 816 (8 × 16 mesh) adsorbed the least (1.0 mg/g). Increased adsorptive capacity was associated with smaller carbon particle size; however, smaller particle size also impeded column flow. Carbon filtration is a practical means for removing benzocaine from treated water.
We conducted several seasonal aquarium experiments to determine survival and body chemistry changes of Atlantic salmon ( Salmo salar ) after 24‐h exposures to salinities of 0, 16.5, 33, and 40‰ at 10°C. Fish transferred directly to test aquaria from an ozonated, 100‰ closed water‐reuse system at 18°C were compared with fish acclimated to single‐use water at 10°C for 1–3 weeks before salinity challenges in solutions of sea salt. In the initial (December and January) challenges, all Atlantic salmon from the closed system with a fork length of at least 200 mm survived exposure to 16.5 and 33‰ salinity, but not 40‰; fish 135 mm long or shorter did not survive exposure to 33‰ salinity. In later experiments, prior acclimation of fish to single‐use water at 10°C helped protect them against exposure to high salinity (i.e., 33 and 40‰) at 10°C. Few fish that were moved directly from the water‐reuse system into test aquaria lived for 24 h in 33 or 40‰ salinity. Atlantic salmon contained less water at 33‰ than at 16.5‰ or in fresh water, but carcass water content did not differ within salinity treatments between fish previously held at 18°C and those acclimated to 10°C and single‐use water. At each salinity, serum sodium concentration tended to rise less in those fish acclimated to the singleuse system than in those transferred directly from the reuse system to the aquaria. The exposure of Atlantic salmon to an elevated acclimation temperature (18°C) in the water‐reuse system exacerbated the disruption of their ionic exchange at exposures to 33 and 40‰ sea salt. A trace of copper (27 μg/L) in the reused water also may have reduced the salinity tolerance of these fish.
Fingerling lake trout ( Salvelinus namaycush ) were reared for 35 d in water with total dissolved gas pressures of 46, 78, 108, or 159 mm Hg above ambient conditions (▵P). Within each gas pressure treatment, daily feeding rations were (1) 1.7% of the total weight offish in the heaviest of three replicates, (2) 1.7% of the weight of fish in each individual tank, or (3) 0.9% of the weight in each tank (underfeeding). Signs of gas bubble trauma were first observed as hemorrhagic spots on the eyes of some fish reared at ▵P = 46, and external evidence of trauma increased as ▵P increased. All fish sampled at ▵P = 159 showed signs of gas bubble disease; the most common were eye hemorrhage and bubble formation inside the mouth. Mortality was 11% or less among fish reared at gas levels up to ▵P = 108. Mortality was as high as 55% at ▵P = 159, but did not differ among feeding treatments. Net weight gain by fish was low at ▵P = 159 because of both high mortality and slow growth. Growth was slowest for underfed fish at all gas levels, and underfed fish consistently showed increasing injury as gas pressures increased. Calculation of feeding rate on the basis of fish weight in individual tanks allowed the most cost‐efficient food distribution. Culture of lake trout at ▵P < 46 is recommended.
Three feeding experiments were conducted with early‐feeding fry of rainbow trout ( Oncorhynchus mykiss ; initial mean weight, 0.10–0.12 g) to determine their need for lecithin contained in soy lecithin (SL), with and without supplemental choline. The source of assay protein was an isoelectric form (RP 100) of isolated soy protein (ISP) in experiment 1, a sodium protein ISP (RP 101) in experiment 2, and an ether‐extracted herring meal in expenment 3. Duration of the feeding trials was 20 weeks for experiment 1 and 16 weeks for experiments 2 and 3. Analysis of variance showed that supplemental SL and choline each increased body weight gain, survival, and body fat, and improved feed conversion (amount fed/weight gain). The extent of beneficial effects varied with type of diet fed. Fish fed either of the ISPs needed at least 4% supplemental SL, either with or without 0.3% choline, for highest survival, but survival of all fish fed extracted herring meal was high. Although choline alone enhanced growth, at least 4% SL, either with or without choline, was necessary for maximum growth.
A comparison of three techniques for the capture of impounded juvenile American shad ( Alosa sapidissima ; 50–100 mm total length) showed a 1‐m‐diameter entrainment net to be an order of magnitude more efficient than a black rectangular tank, which relied on a light source to attract the fish at night. A third technique, pond drawdown, was by far the most efficient, but it also resulted in high (>50%) short‐term mortality. American shad captured by the first two techniques were transported a short distance and placed in circular holding tanks (1.22 or 2.44 m in diameter). After initial treatment with 0.5% sea salts for 1 d and continued culture in 13–15°C water, these fish schooled and fed normally within 1 week, and there was no mortality within 48 h after transfer. Weekly overall mortality rates ranged from 1.8 to 8.4%. Regression analysis showed a significant inverse relation between weekly mortality and number of fish per tank, suggesting that relatively large numbers offish in transport or holding tanks may reduce mortality by promoting stress‐mitigating schooling behavior.
The anesthetic benzocaine was tested for efficacy and safety for spawning-phase chinook salmon (Oncorhynchus tshawytscha) and Atlantic salmon (Salmo salar) at federal fish hatcheries. Tests were conducted in the existing hatchery water supplies (soft water; temperatures, 10–13 °C. Crystalline benzocaine was dissolved in ethanol (1 g/30 mL), and aliquots of that stock solution were added to the water in test tanks. Benzocaine concentrations of 25–30 mg/L anesthetized most fish in less than 3.5 min, and most fish recovered in less than 10 min after 15 min of exposure. Safety margins were narrow; both species tolerated 30 mg/L for about 20 min, but 25 min of exposure caused deaths. For 15 min exposures, concentrations of 35 mg/L for chinook salmon and 40 mg/L for Atlantic salmon were lethal.
A 16‐week feeding experiment was conducted to measure the effects of supplemental dietary aluminum (0, 25, 50, 100, 500, 1,000, 1,500, and 2,000 mg/kg diet) on growth, survival, feed conversion, and proximate composition of Atlantic salmon ( Salmo salar ), mean weight 4.8 g. No significant differences ( P > 0.05) in growth, survival, or feed conversion were found among fish fed the different levels of aluminum. Body fat increased significantly in fish fed aluminum at the rate of 2,000 mg/kg of diet. Total ash was significantly lower in fish fed 1,000–2,000 mg aluminum/kg of diet than in those fed smaller amounts. Differences in concentration of individually measured minerals (aluminum, copper, iron, manganese, and magnesium) were not significant in either carcass or vertebrae of experimental fish. Supplemental dietary aluminum (up to 2,000 mg/ kg of diet) had no measurable beneficial or obvious adverse effect on fingerling Atlantic salmon.
Fry of rainbow trout ( Oncorhynchus mykiss ) were fed, from first feeding (mean weight, 0.12 g), basal diets containing either a nonautoclaved (raw) sodium proteinate form of isolated soy protein (ISP) or the same ISP autoclaved at 0.56 kg/cm 2 and l 10°C for 30 min. In the three‐way factorial, 16‐week study, I measured the effects of autoclaving ISP on the growth, survival, and chemical composition of rainbow trout at three levels of soy lecithin (0, 4, and 8%) and two levels of choline (0 and 0.3%). Fish fed raw ISP grew no faster with or without choline than did those fed the basal diet, but those fed heated ISP with choline showed a quantitatively small but significant advantage in weight gain. Whereas fish fed 4% lecithin with raw ISP more than tripled weight gain compared with fish fed the basal diets, fish fed 4% lecithin with heated ISP grew seven times as fast as those fed no lecithin or choline. Rainbow trout fed choline and 4% lecithin with heated ISP (but not raw ISP) grew significantly faster than those fed heated ISP and 4% lecithin alone. The higher level (8%) of lecithin promoted no more growth than the 4% lecithin with either raw or heated ISP. Among rainbow trout fed heated ISP, 4 and 8% supplemental lecithin – either with or without choline – reduced mortality to the same level, but 8% lecithin was the only concentration that significantly reduced the mortality of fish fed raw ISP. The results of calorimetry and determination of nitrogen with larger (235–375 g) rainbow trout individually held in metabolism chambers indicated that autoclaved ISP enhanced the growth and survival responses offish to lecithin by increasing digestible protein and energy and metabolizable energy. This higher amount of bioavailable energy and protein increased the deposition of body fat.
Benzocaine was tested as an anesthetic on juvenile and mature adult striped bass ( Morone saxatilis ). Concentrations of 55 mg/L at 22°C to 80 mg/L at 11°C effectively anesthetized fish in about 3 min. Recovery was more rapid as temperature increased. Fish survived concentrations of twice the effective concentration and exposure times up to 60 min at the effective concentration. Striped bass required higher concentrations for anesthetization than had been previously demonstrated for salmonid fishes, but safety margins for both concentration and exposure time were wider than for the salmonids.
A 4‐week trial was conducted to determine the optimal feeding level in percent body weight of a commercially prepared, practical diet for early feeding fry of Atlantic salmon ( Salmo salar ) in an ozonated water reuse system at 17–18°C. Triplicate groups of swimup (0.19‐g) fry were fed one of seven levels of Biodiet starter diet calculated for hatchery constants of 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, and 8.5. Feeding levels (percent body weight) were derived at the start of the study and again at 2 weeks by dividing mean body length, in inches, into the respective hatchery constant. Mean body weight and body fat content increased significantly with each increment in level of feeding through a hatchery constant of 6.5. after which there was no further increase. Body protein decreased as feeding increased through hatchery constant 6.5; ash content decreased through hatchery constant 5.5. Results indicated that young Atlantic salmon fed at low feeding rates (2.47–5.44% body weight) in the water reuse system were underfed, but fish fed at 5.46–8.41% body weight grew at a favorable rate.
To examine lake trout ( Salvelinus namaycush ) in the field for cataract and noncataract eye abnormalities, we developed a procedure with a circular 1.7‐power illuminated magnifying lamp. A box in which the lamp is mounted facilitates its transport and provides a support base for the lamp during use in the field. A classification system was developed for assigning nuclear cataracts to four stages based on cataract size as a percentage of the total cross‐sectional area of the lens. When the method was used by newly trained technicians to screen 200,000 fall lake trout fingerlings into cataract and noncataract groups, the error rates were 1.7 and 7.7%, respectively. A technician could examine up to 2,800 fingerlings, 1,300 yearlings, or 700 3‐year‐old fish per day.
The floating towable cage described in this report was used successfully to hold and transport Atlantic salmon ( Salmo salar ) in estuarine waters. These rugged and versatile cages, constructed from readily available, inexpensive materials, were tied singly and in clusters to floating docks in fresh and brackish water, where they withstood strong currents, winds, floods, and tides for 2.5 months without visible damage.
Lake trout ( Salvelinus namaycush ) and Atlantic salmon ( Salmo salar ) fed 30 mg β‐estradiol/kg of feed for 100 d from first feeding had liver and kidney pathology similar to but much less severe than that previously reported for rainbow trout ( Oncorhynchus mykiss ). Mortality was not affected. Both lake trout and Atlantic salmon treated with estradiol weighed significantly less than control fish at the end of the treatment period and at 200 d posttreatment. Testosterone‐treated fish of both species weighed less than control fish at the end of the treatment period. By day 200 posttreatment, testosterone‐treated and untreated lake trout weighed the same, but testosterone‐treated Atlantic salmon were heavier than control fish. Estradiol treatment produced an all‐female population of Atlantic salmon but not of lake trout. Testosterone at 5 mg/kg feed increased the ratio of males to females in both species.
Triplicate 150‐fish lots of first‐feeding fry of rainbow trout ( Oncorhynchus mykiss ; initial mean weight, 0. 12 g) were fed casein–gelatin‐based diets containing 0, 200, 400, 800, 1,000, 2,000, 4,000, or 8,000 mg choline/kg of feed for 12 weeks to determine their need for dietary choline. Although the growth rates of fry were suboptimal, results showed that fry needed no more than 4,000 mg choline/kg casein–gelatin diet for maximum growth and 2,000 mg/kg for maximum body fat and minimum protein. Survival was significantly lower for fish fed 800 mg choline/kg of diet than for those fed greater amounts of the nutrient. These results suggest that the dietary choline requirement of early feeding salmonids is greater than that previously reported for older salmonids. The amount of choline needed by fishes apparently decreases with age or size.
First‐feeding Atlantic salmon ( Salmo salar ) were fed different levels (0, 2, 4, 6, and 8% of diet) of feed‐grade lecithin with and without 0.3% supplemental choline in a diet containing a sodium proteinate form of autoclaved isolated soybean protein. After 14 weeks at 9.2°C, Atlantic salmon fed 6% lecithin with or without added choline had gained the most weight. Fish fed supplemental choline without lecithin gained significantly more weight ( P ≤ 0.05) than did fish fed the basal diet, but choline did not increase weight gain at any level of lecithin. Feed conversion (weight fed/weight gain) improved with increasing lecithin up to 4% and improved even more for fish fed 6% lecithin and 0.3% choline. Only 4% lecithin with or without choline was needed to yield the highest concentration of body fat, but carcass dry matter was highest and ash and protein were lowest in fry fed 8% lecithin alone or 6% lecithin and 0.3% choline. Neither lecithin nor choline influenced mortality, which was low in all groups. Results indicate that 6% dietary feed‐grade lecithin promotes maximum weight gain by swim‐up Atlantic salmon fry fed autoclaved isolated soybean protein as the primary protein.
Laboratory simulation of water temperature regimes that occur in subarctic rivers through winter necessitates the ability to maintain near‐freezing conditions. A heat‐exchanging apparatus is described that provided a convenient means of simulating the range of temperatures (0.5–12°C) that incubating eggs of salmon ( Oncorhynchus spp.) typically experience in south‐central Alaskan watersheds. The system was reliable, easily maintained precise temperatures at our coldest test levels, and was used over several years with few mechanical complications.