Atlantic salmon (Salmo salar) eggs and alevins were raised under conditions where the temperature was systematically varied either at fertilization, at the eyed egg stage, or at hatching. Mortality was more than 20% in eggs started immediately after fertilization at constant incubation temperatures < 4 °C as compared with 5% or less at temperatures > 4 °C. Alevins that eyed at 8 °C and higher were progressively smaller the higher the temperature. The optimum temperature from fertilization to eye pigmentation was near 6 °C. Eyed eggs reared at lower temperatures until hatching were larger than those hatched at higher temperatures. This size differential was maintained until the yolk was completely absorbed at all posthatching temperatures investigated. Sudden decreases in temperature at the eyed egg and hatching stages induced severe edema of the alevin yolk sac, resulting in slower growth and increased mortality.
Hatching of Atlantic salmon (Salmo salar) eggs was delayed or prevented if they were exposed to water of lowered pH (4.0–5.5) after eye pigmentation had developed. Hatching subsequently could be induced by returning eggs to normal pH levels (6.6–6.8). Perivitelline pH fell rapidly to near ambient levels when eggs were exposed to low pH. It is suggested that the observed effects on hatching were due to inhibition of the hatching enzyme, chorionase.Key words: Atlantic salmon, eggs, pH, perivitelline fluid, chorionase
Striped bass, Morone saxatilis (Walbaum), larvae, although physoclistous as adults, initially need to inflate their swimbladders by passing ingested air through a pneumatic duct to the swimbladder. Failure to inflate the swimbladder results in swimbladder atrophy, dysfunctional buoyancy control, deformities, and poor larval survival and growth. The present investigation studied the effects of light intensity, tank colour and photoperiod on the initial swimbladder inflation success of striped bass. In the first experiment, newly hatched larvae were reared for 2 weeks in black or white 350‐L circular tanks exposed to incandescent lighting at 163 or 10 lux. Larvae were fed Artemia from 6 days post‐hatching (dph). The standard length, and oil globule and yolk areas were measured. Swimbladder condition and evidence of feeding were recorded. To study the effects of photoperiod on inflation, larvae were reared in black tanks exposed to either 8 h:16 h or 16 h:8 h light:dark photoperiods at 139 lux. Striped bass inflated their swimbladders between 6 and 9 dph at 17 oC. Inflation success was significantly higher in black tanks (65%) compared with white tanks (42%), but light intensity did not significantly affect swimbladder inflation. Larval growth and food consumption were better in black tanks, primarily because this treatment resulted in more larvae with inflated swimbladders, although larvae with uninflated swimbladders in black tanks were longer at 12 dph than larvae with inflated swimbladders in white tanks. Larvae that successfully inflated their swimbladders fed earlier and exhibited better growth than larvae with noninflated swimbladders. Larvae reared at higher light intensities used up yolk reserves faster. Exposing striped bass larvae to 8 h:16 h light:dark photoperiods resulted in higher inflation rates (55%) compared to larvae reared at 16 h:8 h light:dark photoperiods (30%). Therefore, black tanks and short photoperiods are preferable for early rearing of striped bass larvae to maximize swimbladder inflation success.
The responses of 11 fish species to a continuous pH gradient (usually pH 4–10) were observed to obtain information on avoidance–preference behavior. Under uniform pH conditions, all species were found most frequently near the ends of the apparatus, particularly near the inflow. Imposition of a pH gradient altered the distribution for most species, with the region of lowest pH usually being avoided. Estimated low pH avoidance thresholds were 4.1 for yellow perch, 4.5 for white sucker, 4.7 for brook charr, 5.1 for banded killifish, 5.2 for Arctic charr, 5.4 for common shiner and blacknose dace, 5.5 for threespine stickleback, 5.7 for creek chub, and 5.9 for rainbow trout. Preferred pH ranges were usually 5–7 to 7–9. The distribution of rainbow trout in calcium gradients was not significantly different from that in uniform calcium conditions. Avoidance thresholds of the various species were generally similar to pH levels limiting natural distributions as derived from various lake and stream surveys.
Temperature preference of newly feeding fry of two species of Salmo, three species of Salvelinus, and seven hybrids were determined in a horizontal gradient. Fry of species in the genus Salmo and intergeneric hybrids with female parent in Salmo selected significantly higher temperatures (13.0–15.0 °C, P < 0.05) than did fry of species and hybrids of the genus Salvelinus (9.0–11.5 °C). No significant differences were obtained among species and hybrids within either of the two groups described above. Preferred temperatures of fingerlings (after 3 mo of feeding) of two species and two hybrids within Salvelinus were determined in a vertical temperature gradient. Brook trout preferred 17.5 °C, and lake trout 10.8 °C. The two hybrids (brook trout × lake trout and lake trout × brook trout) preferred intermediate temperatures (14.7 and 14.4 °C). Rainbow trout fingerlings selected 14.7 °C. Key words: temperature, preference, Salmo, Salvelinus, hybrids, gradients
Carleton Un,ivers'ity, Ottawa, Ont. PnrensoN, R. H., eNo J. M. AxoonsoN. 1969. Influence oJ temperature change on spontaneous I'ocomotor actiuity ond. oxygen consulnption of Atlantic salmon, Sal,mo salar, acclimated to two tenxperatures. J. Fish. Res. Bd. Canada 26: 93-109.Measurements of the effect of rapid change in temperature on the spontaneous activity and oxygen consumption were made on Atlantic salmon underyearlings acclimated to 6 or 18 C. The new levels of imposed temperature ranged from 6 to 30 C for both acclimations. At similar test temperatures the calculated standard metabolic rate of the fish acclimated to 6 C was higher than that of the fish acclimated to 18 C, up to about 23 C, where the two curves relating oxygen consumption and temperature intersect. Spontaneous activity could be separaled into two phases, a transient phase occurring during the actual period of temperature change, and a stabilized phase. The transient phase was characterized by a peak in activity which was found to be correlated with the rate, rather than the amount, of the temperature change, In general, the peak was higher for fish acclimated to 18 C. The relation between activity in the stabilized phase and test temperature was characterizedby a plateau or maximum in the general region of the previously determined selected temperature. Except at the coldest test temperature (6 C), the fish acclimated to 6 C were more active in the stabilized phase than were the fish acclimated to 18 C at similar test temperatures. Complete acclimation for both metabolism and activity, between 6 and 18 C, requires about 2 weeks, regardless of the direction of the temperature change.
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