Effect of Female Size, Egg Size, and Water Temperature on

Effect of Fema e Size, Egg Size, and Water Temperature on ogy of Chum S Nitinat River, Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by Hunan Normal University on 06/03/13 For personal use only.

Terry D. Beacham and Clyde B. Murray Department of Fisheries and Oceans, Fisheries Research Branch, Pacific Biological Station, Nanairno, B.C. \/9T %K6

Beacharn, %. D., and @. B. Murray. 1985. Effect s f female size, egg size, and water temperature o n developmental biology of chum salmon (Owcsrhyracheas keta) from the Nitinat River, British Columbia. Can. I. Fish. Aquat. Sci. 42: 1755-1765. We incubated eggs and alevins for five churn salmon /Oncoshynchus &eta) families in each of three female size classes under controlled water temperatures of 4, 8, and 12°C. Egg survival from fertilization t o hatching was highest for eggs from small females and lowest for eggs from large females at a$! three incubation temperatures. Egg survival was highest at 8"C, and at4"C survival rates were largely determined from fertilization t o epiboly, but at 12°C the lowest egg survival rates were recorded from eye pigmentation t o hatching. There were marked differences i n egg survival rates among families. Overall survival rates from egg fertilization t o Fry emergence were most divergent between the large and small female size class at 12°C. Hatching time of the alevins and emergence time of the fry were similar among the three female size classes at each incubation temperature. AIevins hatching at4"C were the longest, but those hatching at 12°C were the heaviest. Larger females produced alevins with both more yo!k reserves and more body tissue at hatching than those from smaller females. The relation between egg weight and subsequent alevin size was dependent upon incubation temperature. At emergence, the longest and heaviest fry were produced b y the largest female size class. Des ~ u f ets des alevins v6sicul6s provenant de cinq families de saumon k6ta (Oncorhynchus keta) reparties en trois classes de ionguepr de femelles s n t kt6 gardes en incubateur dont la temperature de l'eau etait maintersue A 4, 8 et 12°C. A ces temp6ratures, la survie des eufs, de la fertilisation A If6closion, &tail plus 4Bev6e chez ceux provenant de petites fernelles, et plus faible chez ceux issus de grosses femeltes. La survie $tait plus elev6e B 8°C tandis qu'a 4"C, les taux de suwie etaient en grande partie fixes de la fertilisation B If6pibolie; B 12"C, les plus faibDes taux de survie ont et6 observ6s de la pigmentation des yeux A l'6clssion. !I y avait des diffkrences marqu6es entre les taux de survie des e u f s selon la farnille. Pour ce qui est des petites et des grosses femelles, la variabilite des taux de saarvie globaux de la fertiiisation a 0'6mergence des alevins 6tait plus 6lev6e 2i 12°C. be moment de la sortie des alevins vesicul6s et de If6mergence des aievins nageants 6tait semblable ckes les troisclasses de longueur de femelles a chaque temperature d'incubatisn. kes alevins v6sicul6s gardes A4"C etaient les plus Dongs tandis que ceux qui 6taient maintenus Al2"Cetaient Bes plus gros. Par rapport aux petites femelles, Bes grosses femelles ont produit des alevins v6sicul6s possedant de plus importantes rkseaves viteliines et plus de tissu corpsrel a lf6closion. ha relation entre le poids des ~ u f et s la taille ult6rieure des alevins vesicul6s d6pendait de la temperature B ['incubation. A %'6rnergence, les plus gros et les plus longs alevins nageant prsvenaient de la classe des plus longues femelles. Received March 6, 1985 AcceptedjesBy 76,1985 (J8136)

n British CoIumbia, chum salmon (On~&srBkyrach~s ketada)return to heis natal rivers to spawn at 3-5 yr of age (Pritchzd 1943; Rieker 1980; Beacharn and Stan 1982). Body size variation in both sexes in a spawning population may be considerable, especially for males (Beacham a d Murray 1985). Females within a spawning population may differ in postorbitalhypural length by 200rnm, and size variation among female salmon may be an important component of subsequent egg survival (Allen 1957; van den Berghe sand Gross 1984). If egg mortality is related to female size, then variation in female size may be an important component s f population dynamics of a stock. Size sf salmonid alevins and fry may be a significant Can. J . Fish. Aquat. Sci., Vok. 4 2 , 1985

Regu Be 6 mars 1985 Accept6 Be 16 juiB8et 1985

determinant of subsequent growth m d survival (Barns 1969; Fowler 1972). Size sf alevins and fry may be influenced by the size of eggs from which they originate, with lager alevins and k y derived from lager eggs (Srnimov 1975; Kazaleov 1981; Wdlance and Aasjord 19841, but this may not always be the case (Privo19nev1960; Privol'nev et al. 1964; Beacham et 261. 1985). Alevins and fry derived from large eggs we bigger because of the greater amounts of yolk in large eggs than in small ones (Smimov 1975). However, the size of alevins and fry from eggs of different size is dependent upon the efficiency of conversion of yolk to body tissue, and conversion efficiencies are dependent upon water temperatures during incubation ( M m B 966; Heming 1982). Whether or not larger eggs produce lager

Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by Hunan Normal University on 06/03/13 For personal use only.

alevins m d fry may thus be dependent upon the temperature regime during incubation. We investigated the effect of female body length on egg and devin survival under t h e e controlled temperature regimes for a Vancouver Islmd chum salmon stock. The effect of initial egg size on subsequent alevin and fry size under each temperature regime was also investigated to detemine if previous conflicting results were dependent upon the incubation temperature and perhaps stock selected for the experiment.

Materials and Methods We collected gametes from 15 male and female chum salmon from the Nitinat River on the west coast of Vancouver Island on October 3 1, 1983. Postorbital-hypural length of females was measured to the nearest millimetre and scale samples were obtained for subsequent age determination. Sperm from a single male fertilized the eggs of a single female, and after waterhardening, 30 eggs from each family were preserved in 10% f m a l i n for at least 90 d for subsequent detemination of egg size. The diameter of an egg was measured with calipers along the longest axis to the newest 0.1mm. Egg weight (milligrams) was obtained by first blotting the egg to remove excess surface moisture, and then weighing the egg on a top-loading electrobalance. Eggs were incubated in vertical stack incubators, with each tray partitioned into 20 compslhqments with a plastic divider. Three egg lots from each family were assigned to each of three stacks, with each replicate in a different tray in each stack. The trays were kept in darkness and provided with a flow of 6.9 Llmin of dechloginated Nanaims tap water. Target incubation temperatures of 4, 8, and 12°C were set for each of t h e stacks, respectively, and observed temperatures (and standard deviations) from egg fertilization to hatching were 4,0 (0.231, 8.0 (0.18), and 12.0°C (0.16), respectively. Mean water temperatures from fertilization to emergence of the fry were 4.0 (0.21), 8 -0 (0.20), and 12.0°C (0.191, respectively. Water temperatures in each stack were recorded daily. Oxygen concentrations were above 90% of air saturation at each temperature. Dead eggs were removed from each compartment and stored in Stockad's solution (Rugh 1952). All dead eggs were inspected to detemine which were unfertilized or the stage of development at which they died. We recognized three stages of development: fertilization to epibsly (stage 17 of Vernier 19691, epiboly to eye pigmentation (stage 25), and eye pigmentation to hatching (stage 30). Within 1 6 of 50% hatching, 10 alevins from each compmment (30lfmily) were preserved in 10% fomdin for subsequent detemination of length and weights. After hatching, the devins were provided with a gravel substrate, with particle size 2-3 cm in diameter. After preservation for 90 d, alevins were blotted to remove excess surface moisture, and total (fork) length was measured to the nearest 0.1 mm. Total weight of the alevin was also recorded. The yolk was then separated from the rest of the body tissue and weighed. Tissue weight was then determined by subtraction. Dead alevins were removed from each compartment and the number recorded to determine survival rates from hatching to fry emergence. We used an emergence trap (modified from Godin 1980) to detemine timing of fry emergence. We constructed the trap from a Plexiglas aquarium bottom filter complete with lid and standpipe by placing a 4-cm layer sf gravel in the bottom of the filter and fitting a layer of reinforced black plastic cut to fit over the standpipe and the gravel. A 6-mm hole was cut in the plastic

to enable fry to move out of the gravel when they emerged. These traps, each with its own air supply, were placed in 250-E tanks of water at the appropriate temperature. Thirty aslevins from each f m i l y (10lreplicate) were placed in the gravel when they were a b u t two thirds "buttoned-up', (late Vernier stage 35). The emergence traps were exposed to fluorescent lighting during the working day and natural light during the remainder of the day. The emergence traps were checked each afternoon for emergent fry. When 50% of the fry for a particular family had emerged, the remainder of the family in the stack was preserved in 10% fomdin. After preservation for 98 d, 14 fnylreplicate were unselectively drawn from the preserved sample and fry fork length, total weight, yolk weight, and tissue weight determined as for devins. Females were groupd into three size classes based upon their postorbital-hypuml length (Table 1). Ages were determined from scales. Heterogeneity of egg and alevin survival rates m o n g size classes and among families within classes was tested by likelihood ratio (G-statistic) (Sokal md Rohlf 1969)- Equality of alevin and fry lengths and weights m o n g the replicates was tested by doubly nested analysis of variance using the following model (temperatures separate): where Y = length or weight, S = size class 4 k = 1 a d 31, F = family within size class ( j = 1 and 5), R = replicate within fmily ( k = 1 and 3), m d e = e m r tern for the lth observation in subgroup ijk. All effects were considered random. Egg size differences among size classes and among families within classes were tested by a similar model without the replicate term. Equality of alevin and fry lengths and weights among temperatures, size classes, and families was tested with the following model (all effects random): where Y = length or weight, T = temperature (i = 1and 3), S = size class ( j = 1 and 3), TS = temperature and stock interaction, F = family within stock (k = 1 and 51, and e = emor tern for the Ith observation in subgroup ijk.

Results Femde and Egg Size Females were grouped into three size classes based upon their psstohital-hypural length ('"age ," "medium," and "small"), and there were significant differences in length among the classes (F = 43.99, df = 2'12, P < 0.01) (Table 1). Although there was significant variation in egg diameter among families within size classes ( F = 16.27, df = 12,435, P < 0.01), there was no significant difference among size classes relative to variation within the classes (F = 1.95, df = %,12,P > 0.05). There were significant differences in egg weight both among families within size classes (F = 3 1.98, P < 0.01) and among classes ( F = 7.19, P < 0.05). Females in the small size class had lighter eggs than those in the larger size classes. Egg diameter and egg weight were dependent upon female body length. As female body length increased, egg diameter also increased ( r = 0.56, df = 13, P < 8-05),as did egg weight ( r = 8.65, B < 0.01), but more sf the variance in egg weight was accounted for by female length than by egg diameter. Subsequent analysis of variation resulting from egg size differences is based solely on egg weights. Can. J . Fish. Aquar. Sci., Vob. 42, 1985

egg density. Eggs from luge females were less viable than those from smaller ones. Incubation temperature had a marked effect on egg survival. Egg survival was lower at 12 and 4°C than at 8°C for all three size classes (Tables 2, 3). At $"G, egg survival rates of all three hngth Age Egg diameter weight size classes were at least 96%. Differences in survival rates at Class Femde (m) (yr) (mm) (mg> 8°C and those at 4 and 12°C became larger as female size increased. For example, eggs from small-females had 88% Z 6645 Large 8'2(0-2) 303'7(12' survival rates at 12°C and 97% at 8'C, a differential of 9%, 4 8.6(Q.3) 348.9(19.8) 2 m 8.4(0.2) 315e8(14a6) whereas eggs from large females had survival rates of 77 and 3 640 4 594 4 8.2(0.2) 300.-~(7.3) 9696, respectively, a differential of 19% (Table 2). Eggs from 5 623 4 8.5(0.2) 3 1 4 . q 9.5) large females were more sensitive to temperature extremes than Mean 612.4 4.0 8.4(0.2) 316.6(12.7) were eggs - - from small females. Egg survival at 4°C was largely determined by survival rates 8.4(0.4) 332.7 (47 Medium 1 572 36$e6(47.7) from fertilization to epiboly. Egg mortality at this stage was 2 565 806(0.4) 284.0(31.5) higher at 4°C than at higher incubation temperatures (Table 2). 3 8.1 (0.3) 3 540 282.1 (21 -7) At 12'C, the lowest egg survival rates were recorded from eye 3 $.3(0.2) 4 538 283.8(27 -9) pigmentation to hatching for eggs from all three size classes of 5 534 3 7.9(0.2) Mean 549.8 3.6 8.3(0,3) 3 10.2(35.2) females. The stage of development where most mortality occurs Small 1 502 8.2(0.3) 275. (23. during incubati& is clearly bependent upon temperature. 230.2(29.0) Variability in egg survival rates among families within each 3 7.9(0.3) 2 525 268.5(24.4) size class was greatest at 4 and 12°C (Fig. B ;Table 4). Although 3 $.2(0.3) 3 532 4 510 3 8.0(0.3) 263.8(19.2) there were significant differences in egg survival rates among 5 517 3 8.4(0.3) 246.7 (22.5) the size classes at each temperature, heterogeneity in survival lvfem 5 17.2 3.0 8- 1 (0-3) 257.W23.6) rates among families within each class was greater than heterogeneity among the size classes at each temperature (Table 4). Survival rates among families within a size class could vary Survival from 45 to 100% at a given temperature (Fig. 1). Family variation in egg survival rates could be considerable, and was Egg survival from fertilization to hatching was highest for accentuated as temperatures became more extreme. eggs from small-sized females and lowest for eggs from At 8 and 12"C9alevin survival in the small size class was large-sized females at all thee incubation temperatures (Table always higher than those in the two larger classes (Table 21, but 2). Egg densities also increased from the small to the large size the differences between pairs of classes were not always class, but egg mortality rates were not related to initial loading significant (Table 4). AIevin survival increased as incubation densities. For example, within a size class, bere was no relation between family loading density and subsequent family survival temperature declined, with 188% alevin survival observed at 4°C in d l 15 families examined. The alevins that died at B 2°C within each temperature (%2"C9 large r = 0.19, medium r = 0.45, small r = 0.84; 8"C, large r = 0.92, medium r = 0.79, died a few days after hatching and were characterized by sluggish movements and a fungus infection in the gills shortly small P = 8.68; 4'C, luge r = 8.12, medium r = 0.32, small before death. P' = 0.8 1). In fact, d l correlations between loading density and subsequent survival of families within size classes were all As with eggs, variability in alevin survival rates among families within size classes was greater than variability among positive, which suggests that differences in egg survival rates the size classes (Table 4; Fig. I). Alevins from some families among the different size classes were not dependent upon initial


TABLE1 . Postorbital-hypurd length, age, egg diameter, and egg weight of 15 Nitinat River chum salmon females. Females were divided inta thee size classes. Standard deviations are given in parentheses. Thirty eggs were measured and weighed for each female.

TABLE2. Survival rates sf eggs and devins for thee size classes of Nitinat River chum salmon females incubated at controlled water temperatures of 4 , 8 , and 12°C. Times of 50%hatching sf the alevins md 50% emergence for the fry w e indicated. N is number of fertilized eggs (for egg survival rates) or alevins hatching (for devin swival rates). Standard deviations of hatching and emergence time are given in parentheses.

E%gs

Alevins Time to

Eplbsly Temperature Class

("c)

N

Fertilization to epiboly

Can. J . Fish. Aquat. Sci., Vol. 4 2 , 1985

to

eyed

Eyed t Fertilization hatch to hatch

568%

hatch (4

N

Time to Hatch Fertilization 50% to to emergence emergence emergence (a

TABLE3. LikeIihood ratio (6-test) for heterogemeity of survival rates of eggs and alevins from three size classes of Nitinat River female chum salmon. Eggs and alevins were incubated at controlled temperatures of 4, 8, and 12°C.

*P < 0.05.


Eggs

12°C vs. 8°C Large Medium Smdl

Alevins

df

G

df

3 1 1 1

1023.2*

3 I I 1

558.6*

303 .O* 161 .$*

G

2207.2" 929. I* 690.5" 587.6"

12°C vs. 4°C Large Medium Small

8°C vs. 4°C Large Medium Smdl

c h than did others, and the survival rates were survived ~ ~ u better not related to initial a l e ~ i ndensity. Overall survival rates from egg fertilization to fry emergence were most divergent between the smdl and luge size classes at 1YC. Hatching and Emergence Time Eggs derived from females of different length all hatched at the same time when groups incubated at the same water temperatures were compaed (Table 2) (all P > 0.05). Emergence timing sf the fry was also similar among the t h e size classes at each temperature (all P > 0.05). In the Nitiwat River stock, eggs fertilized at the same time and subjected to the same incubation temperatures produce fry that emerge at the same time from the emergence traps. As expected, hatching and emergence time increased with declining water temperature. Alevin Size No significant differences in alevin or fry length and weight were detected among the replicates for individual females, and the replicates were combined for further analysis. Alevins hatching at 4°C were the longest and those at 12°C were the

shortest (Table 5: Fig. 2) ( F = 60.75, df = 2,4, P < 0.01). Alevins derived from lmge females were longer than those from small ones ( F = 4.95, df = 2,16, P < 8 -05) (Table 5 ) . There were significant differences in alevin length among families within size classes ( F = 13.51, df = 12,1314, P < 0.81). Egg weight was shown previously to be significantly related to female body length (Table I), and we examined the relationship between egg weight and alevin length at each incubation temperature. Although all three correlations were positive, the only one approaching significance was at 22°C ( r = 0.45, df = 13, 0.05 < B < 0.18) (Fig. 3). The effect of egg size on subsequent alevin length was dependent upon the incubation regime used. The total weight of alevins at hatching was dependent upon both incubation temperature ( F = 23.2 1, P < 0.01) and female length ( F = 129.73, P < 0.01) (Table 5). Given the variation in egg weight among families within size classes (Table I), there were also significant differences in total weights of alevins among families within classes ( F = 86.563, P < 8.01). Total weight of alevins declined as incubation temperature declined and large females produced heavier alevins than did small ones. The-total weight of an alevin may be partitioned into the weight of the yolk and that of the body tissue. Although there significant differences in total alevin weight among incubation temperatures, with the heaviest alevins produced at 1 2 0 ~there , were no differences in alevin yolk reserves at hatching within a size class attributable to incubation temperaNre (F-= 5.30, P > 0.05) (Table 5). There were, howiver, c l e a differences in alevin yolk reserves attributable to female size ( F = 100.59, P < 0.01) and variation among families within size class ( F = 188.51, P < 0 -0I). Large females produced alevins with greater yolk reserves. As there were significant differences in total alevin weight among incubation temperatures, but not yolk weight, there must be diffe~ncesin devin tissue weight ( F = 74.8 4 , P < 0.02). Within each size class, alevins with the heaviest tissue weight were produced at 1TC, and the lightest at 4°C (Table 5). Alevins from large females also had greater tissue weights at each temperature than did those from small females ( F = 78.32, P < 0.81). Alevin tissue weight at hatching is clearly influenced by the efficiency of conversion of yolk to body tissue at the different incubation temperatures. Alevin tissue weight -at hatching was positively correlated with initial egg weight at all three incubation temperatures, but

TABLE4. Likelihood ratio (G-test) for heterogeneity of survival rates of eggs and alevins from three size classes of Nitinat River female chum salmon. Eggs and alevins were incubated at controlled temperatures sf 4, 8, and 12°C. "B < 0.05. 12°C Egg

df

G

8°C Alevin

df

6;

Egg df

6

Alevin df

Total

4°C

Egg

df

G

6;

Alevin df

G

Egg df

Standardized measure

Alevin df

G

6

Egg

Alevjin

Among sizes 2 Within sizes 12 Large 4 Medium 4 Small 4 Luge vs. medium 1 Large vs. small 1 Medium vs. small I Total

14 Can. J . Fish. Aquat. Sci., VoE. 42, 698.5

1758

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