Experimental sea ranching of brook trout, Salvelinus fontinalis Mitchill

An experiment to induce anadromy in a population of wild brook trout, Salvelinus fontinalis , was conducted near Sept-Iles, Quebec, in 1978–1979. Brook trout were captured from the Matamek River, tagged and transported to the Matamek River estuary during late spring and early summer, and allowed free movement between an impassable waterfall 0.7 km upstream and the sea. Fish were recaptured in autumn as they returned to fresh water. Over two years, 34.0% of the released fish were recaptured. Best returns were in the 2+ and 3+ age classes with 38.0 and 62.1% recaptured, respectively. Straying of transplanted fish appeared to be <1%. All age classes included sea run brook trout (sea trout) but the largest percentages of sea trout occurred in older fish. Growth was better in sea trout than in fish which did not develop anadromy, presumably a function of an increased food supply at sea. Severe tagging effects stunted growth and probably suppressed anadromy, especially among younger fish. Sexual characteristics of recaptured fish indicated suppressed maturation of gonads in sea trout compared to fish remaining in fresh water and there was a shift to a larger percentage of females in the sea trout. Comparisons between our results and data on other anadromous Salvelinus species underscore the potential for sea-ranching of trout and char as a moderate effort, high yield aquaculture technique.     

Distribution of fingerling brook trout, Salvelinus fontinalis (Mitchill), in dissolved oxygen concentration gradients

A self-recording linear gradient tank and procedures are described in which individual brook trout fingerlings unstressed by recent transfer, unaccustomed surroundings or the presence of an observer could move freely in 16 oxygen concentration gradients within the limits of 1 and 8.9 mg O₂1⁻¹. They avoided oxygen concentrations below 4 mg 1⁻¹ most of the time and preferred 5 mg 1⁻¹ or higher more than half the time, which supports the field-derived belief that fish avoid oxygen concentrations below 5 mg l⁻¹ in the natural environment if they can.     

Action spectrum and quantal thresholds of retinomotor responses in the brook trout,Salvelinus fontinalis (Mitchill)

Summary The radiant energy per unit area required to trigger retinomotor responses was determined for eight wavelengths. The curve's maximum at 520 nanometres corresponds to two microwatts per steradian per square metre. The threshold requires the absorption of 7000 quanta per second per square degree of the field by the scotopic pigment.

---

Zusammenfassung Die je Einheitsbereich erforderliche Strahlungsenergie für die Auslösung der retinomotorischen Reaktion wurde für acht Wellenlängen gemessen. Das Maximum der Kurve (520 Nanometer) entspricht zwei Mikrowatt pro Steradian pro Quadratmeter. Im Bereiche des Schwellenwertes ist eine Absorption des Feldes durch das skotopische Pigment von 7000 Quanten pro Sekunde, pro Quadratgrad benötigt.

---

---

Supported by a grant from the National Research Council of Canada.     

Seasonal changes in the physiology of brook trout, Salvelinus fontinalis (Mitchill), in a sub-Arctic river system

Wild herring larvae were sampled from the Firth of Clyde, Scotland in 1980 and 1981 to assess the suitability of otolith ageing methods for herring larval studies. The ages and growth rates were estimated directly from otolith ring counts, by comparison of ring counts with the results of validation studies on reared larvae of known age, and by back-calculation. Growth rates based on otolith data were compared with indirect calculations based on length at capture. The assumption of daily ring deposition, even allowing for a period of lag before the initiation of daily ring deposition, led to incorrect predictions for age at yolk-sac absorption, and back-calculations led to overestimated growth rates, indicating that ring deposition does not begin at hatching and that light microscope counts give a rate different from one ring per day in wild herring larvae.     

Differences in low pH tolerance among strains of brook trout (Salvelinus fontinalis)*

Survival time of brook trout (Salvelinus fontinalis Mitchill) at low pH was directly related to size, and inversely related to temperature. Between pH 2.50 and 3.25 an increase in pH by increments of 0.25 each led to a 2–3 fold increase in survival time. At higher pH's (3.25–3.75) elevations in pH by the same increments each produced a 3–5 fold increase. Brook trout tested at pH 3.35 and 3.50 showed maximum survival times in June-August. Members of seven inbred lines of brook trout were tested for acid tolerance; the lines differed markedly providing strong evidence that acid tolerance is hereditary. Tests involving either intercrossed or backcrossed offspring of tolerant or intolerant parentals demonstrated intermediate survival in 12.5% of all experiments and heterosis in 66.7% of the tests. Differences in survival of inbred lines were the most marked at pH 3.25. Exposure for 1 week at pH 3.75 resulted in a 20–25% decrease in survival time of 18 fish tested at pH 2.50 and 3.00. Out of a total of 24 trout (17 g) tested at pH 3.75 two highly tolerant individuals were still alive after 6.1 weeks. Thus it is likely that a strain resistant to a pH below 4.1, the previously recorded lower limit, can be developed by selective breeding.     

The fine structure of the trout blastoderm, Salvelinus fontinalis (Mitchill)

The Speckled Trout blastoderm at the late high blastula stage is characterized by two different cell populations. The “light” blastomeres comprise one cell type while the “dark” and “medium” blastomeres appear to differ from one another only in degree and thus may be considered as the second type. “Dark” and “medium” blastomeres are irregular in shape, are located centrally and deep in the blastoderm, have an abundance of smooth endoplasmic reticulum with associated 520 Å glycogen particles and a single mitochondrial profile. The “light” blastomeres have randomly arranged glycogen particles in minimal quantities in contrast to the “medium” and “dark” blastomeres and in addition exhibit three mitochondrial profiles, which could however represent artifacts. It is postulated that in the Speckled Trout cellular differentiation has commenced by the third day of incubation at 10°C and that this is manifested visually by the appearance of two different cell populations; the more differentiated “dark” and “medium” blastomeres possibly destined to give rise to the hypoblast and the less differentiated “light” blastomeres.     

A dense cell in the epithelium of the gill lamellae of the brook trout, Salvelinus fontinalis (Mitchill)

A cell was found in freshwater brook trout which was similar to a chloride cell as it was mitochondria-rich with an extensive tubular network, but differed in having a dark cytoplasm, large round vesicles in the apical cytoplasm, and large membrane-bound bodies near the nucleus. The base of the cell was separated from the basement membrane by cytoplasm from another epithelial cell. The cell was more rarely found in trout adapted to brackish water and salt water.     

pH preference and avoidance responses of adult brook trout Salvelinus fontinalis and brown trout Salmo trutta

The pH preferred and avoided by wild, adult brook trout Salvelinus fontinalis and brown trout Salmo trutta was examined in a series a laboratory tests using gradual and steep‐gradient flow‐through aquaria. The results were compared with those published for the observed segregation patterns of juvenile S. fontinalis and S. trutta in Pennsylvania streams. The adult S. trutta tested showed a preference for pH 4·0 while adult S. fontinalis did not prefer any pH within the range tested. Salmo trutta are not found in Pennsylvania streams with a base‐flow pH < 5·8 which suggests that S. trutta prefer pH well above 4·0. Adult S. trutta displayed a lack of avoidance at pH below 5·0, as also reported earlier for juveniles. The avoidance pH of wild, adult S. fontinalis (between pH 5·5 and 6·0) and S. trutta (between pH 6·5 and 7·0) did not differ appreciably from earlier study results for the avoidance pH of juvenile S. fontinalis and S. trutta. A comparison of c.i. around these avoidance estimates indicates that avoidance pH is similar among adult S. fontinalis and S. trutta in this study. The limited overlap of c.i. for avoidance pH values for the two species, however, suggests that some S. trutta will display avoidance at a higher pH when S. fontinalis will not. The results of this study indicate that segregation patterns of adult S. fontinalis and S. trutta in Pennsylvania streams could be related to pH and that competition with S. trutta could be mediating the occurrence of S. fontinalis at some pH levels.