Fry Size Research Articles

Comparative developmental biology of pink salmon, Oncorhynchus gorbuscha, in southern British Columbia

Eggs and alevins from 21 families of pink salmon, Oncorhynchus gorbuscha, from five odd‐year broodline stocks spawning in southern British Columbia were incubated under controlled water temperatures of 4° C, 8° C and 12° C. There were significant differences in egg survival among stocks and among families within stocks at all incubation temperatures, but the differences were greatest at 4° C. Alevin survival was at least 97% for each stock at each temperature. The most northern spawning stocks had higher egg survival at 4° C than did the others. Hatching time of the alevins and emergence time of the fry were similar for all five stocks. Alevins hatching at 8° C were longer than those hatching at 4°C or 12°C, but there were no stock differences in alevin length or tissue weight. Stocks with larger eggs produced alevins of greater total weight and more yolk. Emergent fry from Vancouver Island stocks had the greatest tissue weight at 12° C, but Fraser River fry were heaviest at 8° C. There were significant differences among families within stocks for alevin and fry size parameters, suggesting that family variation should be accounted for in studies of salmonid developmental biology.

Effect of egg size on incubation time and alevin and fry size in chum salmon (Oncorhynchus keta) and coho salmon (Oncorhynchus kisutch)

Variability in hatching time, time of exogenous yolk absorption ("button up") of alevins, alevin size, and fry size was investigated with respect to initial egg size for chum salmon (Oncorhynchus keta) and coho salmon (Oncorhynchus kisutch). There was no significant difference with respect to egg size in hatching time of the alevins (stage between hatching and emergence from the redd) or time of exogenous yolk absorption for either species. For both species, alevins hatching from large eggs were longer and had greater amounts of yolk than those hatching from small eggs. Tissue weights of the alevins were not different. The differences in size between these two groups of alevins were maintained throughout the alevin stage and were greater at exogenous yolk absorption than at hatching. Fry (newly emerged, free-swimming young) derived from large eggs had greater tissue weight at exogenous yolk absorption than those derived from small eggs.

Comparison of Three Instream Incubation Techniques for Coho Salmon

Abstract As part of a strategy to rear salmonids semi-naturally, three instream incubation techniques were evaluated in 2 successive years in a diversion channel of the Big Qualicum River on Vancouver Island in British Columbia. Fertilized coho salmon (Oncorhynchus kisutch) eggs were (1) placed on screens above a single layer of gravel in fish- and light-tight boxes (shallow matrix), (2) interspersed with cleaned gravel in enclosed areas of existing riffles (deep matrix), and (3) interspersed with gravel in small screen cages (baskets) buried in the center of cleaned areas of the riffles. The shallow-matrix units were the least effective, mortality was extensive, and fry size, stage of development, and efficiency of yolk conversion were all relatively inferior. The basket technique was best in the second year, when mean survival was 68%, fry lengths were the largest, rate of development the fastest, and yolk conversion the most efficient. Performance of the deep-matrix boxes was intermediate in effectiven...

Weight and Length Variability of Swim-Up Atlantic Salmon Fry as an Indicator of Incubation Efficiency

Abstract Evaluations of length, weight, and volumetric displacement data of swim-up Atlantic salmon fry (Salmo salar) from two deep-substrate incubators indicate similarities of average fry size between the two incubators but discrepancies in average fry size among subdivisions within each incubator. Observed differences are thought to be due to deficiencies in water circulation within the incubation medium at the time of hatching. Modifications to basic incubator design are suggested to overcome these water circulation deficiencies.

Logging Impacts and Some Mechanisms that Determine the Size of Spring and Summer Populations of Coho Salmon Fry (Oncorhynchus kisutch) in Carnation Creek, British Columbia

Natural patterns in emergence times, seaward movements, instream distributions, densities, and growth of coho salmon fry (Oncorhynchus kisutch) between March and September are contrasted with patterns observed during and after logging in the Carnation Creek watershed. After streamside logging in 1976–77, fry emerged up to 6 wk earlier and moved seaward more quickly than during years before logging. These observations are attributed to higher water temperatures during the winter and to emergence during a period of more frequent freshets. Increased fry movement from the stream could result in habitat being underutilized. In sections affected by intense streamside logging, the deposition of "fine" logging debris led to increased fry densities during the summers of 1977 and 1978. After major freshets in November 1978, which removed this fine debris and affected channel morphology in these sections, fry densities declined below those observed prior to logging. Growth rate of fry was inversely correlated with density in all stream sections. Growth rates, after correction for density, tended to be greater in all sections after the adjacent streamside was logged. Larger fry and more variable numbers of fry remained in the stream in September after logging than before logging. Their increased size is attributed to the longer growing season afforded by earlier emergence. This complex of interacting factors determines the number and size of fry in autumn and it can influence the production of smolts the following spring.

Quality of Chum Salmon Fry Improved by Incubation over Artificial Substrates

Abstract Chum salmon (Oncorhynchus keta) fry were incubated over one of three artificial substrates and compared with a control group incubated over flat bare screen. Fry incubated over substrate were significantly larger in both mean weight and length (P < 0.001) than fry incubated without substrate. Fry size varied slightly among substrate groups but varied significantly due to tray position. Condition factors indicated that fry incubated over substrate completed yolk absorption sooner than fry incubated without substrate. We theorize that this is the result of lower levels of dissolved oxygen being immediately available to the alevins because they are less uniformly dispersed in the incubation container without substrate. Low levels of dissolved oxygen are known to retard yolk absorption in other salmonid alevins. Among the three substrate groups, Vexar was determined to be more time and cost effective than the other types of substrate tested.

Significance of Sequential Feeding Patterns of Juvenile Rainbow Trout in a Large Lake-Fed River

Abstract Rainbow trout fry Salmo gairdneri, feeding during the day in a large river below a lake, far more frequently attacked drifting organisms than substrate-associated organisms. Recently emerged fry struck at prey more frequently than did older fry. Zooplankton from the lake upstream were the prey most frequently consumed by small fry, whereas larger aquatic and terrestrial insects were the major food of larger fry. Of those zooplankters fed upon by small fry, large calanoid copepods (mainly Epischura nevadensis) and Daphnia galeata mendotae were selectively consumed and smaller Bosmina longirostris rarely consumed, as would be expected of size-selective predators, but large Cyclops bicuspidatus were also under-represented in fry stomachs. There was a seasonal increase in size of prey consumed. The relative prey size (size of prey consumed divided by fry size) increased throughout the year, except from fall to winter when fry growth was slow. It is suggested that the sequential change in feeding patt...

Nonlinear Relation Between Smolts and Adults in Babine Lake Sockeye Salmon (Oncorhynchus nerka) and Implications for Other Salmon Populations

Data on sampling variability in smolt abundance for Babine Lake sockeye salmon (Oncorhynchus nerka) are combined with a previous analysis to calculate a more accurate estimate of the degree of nonlinearity in the relation between smolts and adults. Results indicate significant within-stock nonlinear mortality, large variability in mortality which tends to obscure any smolt-to-adult relation, or both. Analysis of age structure data identifies the first 15 mo of marine life as the period when most of this nonlinear or relation-masking mortality occurs. I also calculate the amount of smolt measurement error below which other salmon stocks are classed as having nonlinear marine survival. A distinct separation between even and odd brood year marine survival of Babine Lake sockeye suggests interactions with pink salmon. Juvenile pink salmon (O. gorbuscha) abundances correlate positively with residuals in Babine Lake sockeye survival for the same seaward migration year. This suggests a depensatory mortality effect which occurs later in the marine life stage than the possible within-population compensatory effect. Depensation is plausible because the size of pink fry equals that of sockeye smolts by August in coastal waters, permitting mutual swamping of predators. The paper concludes with implications for further enhancement.Key words: density dependence, marine survival, measurement error, enhancement, depensation, nonlinear, variability

ティラピアＴｉｌａｐｉａ ｎｉｌｏｔｉｃａの雄性ホルモン処理による雄化の実用化試験

The purpose of the present investigation is to solve some practical problems concerning the complete masculinization in Tilapia nilotica by the oral administration of androgen with special regard to the size of fry at the start of treatment and to the dose of hormone. For this purpose, fry of each of three groups were daily fed on diets containing methyltestosterone (MT) at doses of 50 and 100 μg/g diet for 30 days starting on the day of capture, 5th and 10th day of capture from the pond rearing the adult fish. The complete masculinization of genetic female could be brought about in the 2 groups in which MT at dose of 50 and 100 μg/g diet was administered to fry (under 12.0mm in total length) for 30 days from the day of the capture, though a few ovaries were discernible in both groups on the 16th day after the end of treatment. Remaining 4 groups treated with the same doses of hormone for 30 days from the 5th and 10th day of the capture resulted in the occurrence of intersexual gonads and ovaries. In most cases, these inter-sexual gonads were ovarian in nature in the anterior region, while they were apparently testicular in the posterior region.

Effects of Hatchery Procedures on Later Return of Atlantic Salmon to Rivers in Maine

Abstract The hatchery procedures used at Craig Brook (Maine) National Fish Hatchery in rearing and stocking Atlantic salmon (Salmo salar) into rivers in Maine were tabulated according to 85 variables related to strain, hatching, fry size, growth, water temperature, water volumes, type of feed, disease treatment, living space, stocking date, river conditions, and treatment during transit. Variables in the rearing regime were compared with returns of adult salmon by standard multiple regression statistics to identify possible reasons for variability in the survival rate of hatchery lots planted in different years and rivers. Only 5 of 493 multiple regressions were significant (P = 0.025), and these were associated with water flow and amount of living space during the last few months of life in the hatchery, or with relative water level in the rivers receiving smolts.

The effects of maternal age, relative hatching time and density of stocking on growth rate of fry in the European and Chinese races of the common carp

The effects of genetic and environmental factors (maternal age, relative hatching time and density) and their interactions on the growth rate of carp fry were evaluated. It was confirmed that relative size of fry immediately after hatching is a major determinant of further growth rate, but that the cause of the initial advantage (hereditary or environmental) is of little importance. A theoretical model was developed to express the quantitative relationships between the interacting genetic and environmental factors.

Anomalous Positions of the Plerocercoid of Ligula intestinalis (Linnaeus 1758)

The position of the plerocercoid in the body cavity of rudd Scardinius erythrophthalmus was investigated. It is shown that in 6 fish out of 880 fry examined at one month old, plerocercoids occurred in the pericardial cavity and dorsal muscle tissue whereas in 733 immature fish and 220 adult fish the plerocercoid was recovered only from the body cavity. The anomalous positions of the plerocercoids are discussed, and it is suggested that the small size of the rudd fry and the short duration of the plerocercoid in the body cavity prevented site recognition, and may have resulted in the anomalous positions.

Co&lt;sup&gt;60&lt;/sup&gt;腹腔内標識によるニジマス稚魚の天敵の追跡

At about noon of May 1st, 1960, 191 individuals of rain-bow trout fry, in which 39 fish had a Co60 pin radiation source (about 100μc) inserted in the abdominal cavity of each, were liberated close to the midpoint of the same stream that was used in the last Zn65 injection experiment (Fig. 1). Since that afternoon, the vicinity around the stream was monitored by Crystal Scintillation Survey Meter (11/2 NaI Crystal) and by G-M Survey Meter at least once a day, and the locations where the radiation sources were detected, were recorded on the map. (Fig. 1) The recovery of these Co60 marked fry and the Co60 pins outside the liberated fry was done first from 9th to 11th of May and secondly from 26th to 29th of July. By these efforts, 36 pieces of Co60 pins were recovered in total. 1) 21 individuals of living fry carrying the Co60 pins inside their body (F in Fig. 1), 2) 10 pieces of the pins found on the bottom sand of the stream (S), 3) 5 pieces of the pins found in the holes under rocks (R). About the 10 pieces of Co60 pins found on the bottom sand, it was thought to be caused by the predation and the excretion of adult trouts. If it was really so, the adult trouts had taken about 1/4 of the liberated fry within 8 days. About the 5 pieces of the pins found in the holes under huge rocks, we could not think of any cause other than the result of the predation and the excretion of Japanese water shrew, Chimarrogale platycephala, nested in the experimental area (Fig. 2 and 3). The quantity of predation during 8 days by this mammal was estimated as about 1/8 of total fry liberated. However, the predation by a wild bird, Cinclus pallasii, the most powerful predator in the last year's experiment, was not recognised, though a couple of this birds with two youngs were very often found flying in the experimental area. One of the reason why the bird did not predate the fry, was thought to be that the size of fry liberated in this year (average 8 gr.) was much larger than that of last year (average 1.2 gr. for small sized group and 2.7 gr. for large sized group). Moreover, it might be caused by that the distance from the point of liberation to the nest of this bird in this year was farther than that of last year. The nest was found just above the point of liberation in last year, but was not found in and near the experimental area this year.

Erratum to : Egg Diameter and Size of Fry of the Rainbow Trout

Erratum to : Egg Diameter and Size of Fry of the Rainbow Trout

The Growth of Brown Trout (Salmo Trutta Linn.)

ABSTRACT Groups of trout fry of the same parentage were grown in environments where the following factors were controlled : temperature, amount and intensity of illumination, rate of water flow, aeration and chemical composition of the water, amount of living space and quality of food supply. They were allowed to eat as much as they would, and individual weights were recorded during the first 8 months after the beginning of feeding. There was soon an increase in the range of individual weight in each group of fry, and thereafter the larger fry grew faster than smaller ones. When the larger fry were removed, the smaller ones grew at an increased specific rate, and when larger fry were added, the smaller ones grew more slowly. It is suggested that a ‘size hierarchy’ was established within each group, and an individual’s specific growth rate depended on its position in the order of decreasing weight. There was an optimum degree of crowding for maximum productivity. Compared with the fry in this group, the specific growth rates of individuals in larger, more crowded groups depended on the number of fish of larger size, while in smaller, less crowded groups, individuals grew at rates depending on the proportion of fish which were larger and smaller. Alevin weight had little effect on the specific growth rates of fry. There were differences between the growth histories of fry derived from alevins of the same weight and descended from the same father but different mothers (all of the same stock, age and size). The specific growth rates decreased as the fry grew older, but there was no correlation between body weight and specific growth rate, except for the size hierarchy effect within each group. This effect had a greater influence on the size of individual fry than had either alevin weight or heredity.