Larger Fry Research Articles

Revisiting the restricted movement paradigm: the dispersal of Atlantic salmon fry from artificial redds

The restricted movement paradigm (RMP) asserts that stream fishes are sedentary, living much of their lives within a single reach. To test the RMP, we implanted eyed Atlantic salmon eggs (Salmo salar) into a total of 19 artificial redds, in seven salmon-free streams, in 6 years, and estimated summer fry dispersal through electrofishing surveys. As expected, most fry dispersed downstream, but an average of 35% moved upstream. Surprisingly, fry moved just as far upstream as downstream (medians = 403 and 404 m, respectively). Fry were larger at lower densities and farther from redd sites, consistent with density-dependent growth, and larger upstream than downstream, possibly indicating that larger fry were better able to move upstream against the current. Dispersal distances were normally distributed around all but two of 19 redds, and half of the downstream dispersal curves were best described by unimodal distributions, consistent with a homogeneous movement strategy. Our data suggest that salmon fry were more mobile and move upstream more than previously thought, which should facilitate their stocking or reintroduction to new habitats.

Unnatural selection of salmon life histories in a modified riverscape.

Altered river flows and fragmented habitats often simplify riverine communities and favor non‐native fishes, but their influence on life‐history expression and survival is less clear. Here, we quantified the expression and ultimate success of diverse salmon emigration behaviors in an anthropogenically altered California river system. We analyzed two decades of Chinook salmon monitoring data to explore the influence of regulated flows on juvenile emigration phenology, abundance, and recruitment. We then followed seven cohorts into adulthood using otolith (ear stone) chemical archives to identify patterns in time‐ and size‐selective mortality along the migratory corridor. Suppressed winter flow cues were associated with delayed emigration timing, particularly in warm, dry years, which was also when selection against late migrants was the most extreme. Lower, less variable flows were also associated with reduced juvenile and adult production, highlighting the importance of streamflow for cohort success in these southernmost populations. While most juveniles emigrated from the natal stream as fry or smolts, the survivors were dominated by the rare few that left at intermediate sizes and times, coinciding with managed flows released before extreme summer temperatures. The consistent selection against early (small) and late (large) migrants counters prevailing ecological theory that predicts different traits to be favored under varying environmental conditions. Yet, even with this weakened portfolio, maintaining a broad distribution in migration traits still increased adult production and reduced variance. In years exhibiting large fry pulses, even marginal increases in their survival would have significantly boosted recruitment. However, management actions favoring any single phenotype could have negative evolutionary and demographic consequences, potentially reducing adaptability and population stability. To recover fish populations and support viable fisheries in a warming and increasingly unpredictable climate, coordinating flow and habitat management within and among watersheds will be critical to balance trait optimization versus diversification.

Who will become dominant? Investigating the roles of individual behaviour, body size, and environmental predictability in brown trout fry hierarchies

Abstract This paper presents a study investigating performance of brown trout fry, with different behavioural characteristics, in environments differing in food predictability. Based on previous experimental findings, we hypothesised that more active individuals would be favoured by a predictable environment, as compared to an unpredictable environment, as a consequence of being more aggressive and likely to dominate the best feeding stations. This hypothesis was not supported, as more active individuals instead tended to perform better, in terms of growth and survival, in unpredictable environments. However, this effect may stem from initial size differences, as more active fish also tended to be larger. In predictable environments, no trends between activity (or size) and performance were detected. Dominant individuals could be identified based on lighter body colouration in 9 out of 10 rearing tanks, but dominance appeared not to be related to activity score. The results highlight a potential advantage of more active and/or larger fry in unpredictable environments, while performance in predictable environments is likely depending on other phenotypic characteristics. Our general experimental approach can be useful for further developments in the investigation of performance of different ethotypes of brown trout fry.

Cascading effect of exotic fish fry on plankton community in a tropical Andean high mountain lake: a mesocosm experiment

<p>Fishless Andean high mountain lakes may be vulnerable to fish invasion because they tend to be small, oligotrophic and contain low zooplankton diversity. During the first decades of the twentieth century, rainbow trout, <em>Oncorhynchus mikiss</em>, was introduced in South America, and stocking of juvenile stages (fry) in lakes continues today. However, their effect on plankton in these lakes has been little studied. We performed a mesocosms experiment to assess effects of trout of different ontogenetic stages on zooplankton and phytoplankton in a tropical-Andean high mountain lake. The presence of trout fry resulted in declines in several large zooplankton taxa, increases in chlorophyll <em>a</em> and dissolved inorganic nitrogen (DIN). Our results showed that small fry consume large copepods (<em>Colombodiaptomus brandorffi</em>) at a faster rate than larger fry, and also consumed medium sized copepods (<em>Tropocyclops prasinus</em>) that are not affected by the larger trout fry. Fish of both sizes consumed <em>Ceriodaphnia quadrangula</em>, a midsize cladoceran. Fish predation had weak effect on the phytoplankton biomass, but we found a correlation between zooplankton biomass and phytoplankton richness, and significantly larger cell of the alga <em>Peridinium</em> in the presence of fish. Our results indicate that trout introduction produces cascading ecological and phenotypic effects on the plankton communities of tropical mountain lakes, similar to those observed in temperate latitudes.</p>

Effect of brood stock size on egg fertilization, hatchability and fry survival rate of African catfish (<i>Clarias gariepinus</i>)

This experiment was conducted to investigate the effect of size of brood stock on egg fertilization, hatchability and fry survival rate of Clarias gariepinus in an intensive culture system, for a period of four weeks. Larger brood stock size (1200-1500g) produced larger eggs and bigger fry while moderate brood stock size (795-1000)g produced moderate eggs and moderate fry. The mean size of eggs produced and the size of brood stock was however not significantly different (p > 0.05). In addition, larger eggs resulted in larger fry. The survival rate of fry after starvation increased with increase in parent brood stock size. Best on this study it was recommended that for larger eggs and fry production, brood stock of Clarias gariepinus , of average size of (1200-1500g) should be selected for use in fish hatchery operation in Nigeria. There was no significant difference (p> 0.05) in the physiochemical parameters. Keywords : Broodstock, Egg fertilization, Hatchability, Clarias gariepinus

Large-scale dispersal of the larvae of nearshore and pelagic fishes in the tropical oceanic waters of French Polynesia

The larvae of tropical pelagic and reef fishes were sampled from October 1995 to August 1997 using a very large fry pelagic trawl at sites between 4 and 20° S and 134 and 154° W in the region of the Society, Tuamotu and Marquesas Archipelagos in French Polynesia. Sites were selected on the basis of longline catches of adult tuna (a predator of larval reef fishes) and acoustic surveys of micronekton to a depth of 600 m. A total of 3369 larvae were collected by 93 net tows. Most were late-stage larvae representing 29 taxa, of which 26 were predominantly reef fishes. Samples were dominated by acanthurids (43%), pleuronectiform larvae, ostraciids, fistularids, balistids, holo- centrids, chaetodontids, mullids and carangids. Distance to reefs was the principal factor determining clustering patterns in classification and ordination analyses, and offshore samples (>150 km from reefs) were dominated by pelagic species, while collections nearer to reefs were dominated by coral reef species. There was a linear decline in richness of samples with increasing distance from reefs and an exponential decline in abundance, so that few reef fish larvae were collected >300 km from adult reef habitats. However, abundances of up to hundreds of reef fish larvae per hour of net tow were collected >100 km from the nearest reef. Our results show that relatively little connectivity is likely among reef systems separated by >300 km in French Polynesia, but substantial exchange of larvae within a restricted range of reef fish taxa might occur at smaller spatial scales.

A farmer-oriented Nile tilapia, Oreochromis niloticus L., breed improvement in the Philippines

Opportunities for developing small-scale tilapia industry in the Philippines is hampered by the shortage of good-quality seeds and broodstock. Most small-scale farmers are dependent on distribution centres for improved tilapia seeds that are expensive and not sufficient to meet market demands. An option would be for farmers to develop their own tilapia breeds using simple procedures within their technical and financial resources. This option will also help sustain the diversity of locally adapted domestic stocks of tilapia. The Philippine tilapia production of ∼122 316 MT can be increased by ensuring a stable supply of quality seeds and transferring suitable technology to fish farmers. The study was carried out in a tilapia hatchery/nursery pond in the Philippines to explore the potential for a farmer-based research on tilapia breed improvement using relatively simple artificial selection procedures. One generation of size-specific mass selection based on the early culling of large fry (collimation procedure) was applied on a Nile tilapia strain, Oreochromis niloticus L., in net cages set in a small earthen pond. Two episodes of directional selection were performed after initial removal of large fry at 21 days. Selection of parents and progeny testing were conducted in hapa and B-net cages set in earthen ponds. The selection resulted in a significant response of 8% for standard length and 29% for weight relative to the control. The crude estimates of realized heritability is ∼16% for standard length and ∼26% for weight comparable with similar studies conducted by other workers.

Effect of broodstock size on egg and larval size and survival of larvae of the African catfish, <i>Clarias gariepinus </i>under laboratory conditions

Effect of broodstock size on egg and larval size and survival of larvae of the African catfish Clarias gariepinus was investigated under laboratory conditions for a period of 21 days. Larger broodstock size (600 – 1099 g) produced larger eggs and bigger larvae while smaller broodstock size (300 – 599 g) produced relatively smaller eggs and smaller larvae. The mean size of eggs produced and the size of broodstock was however not significantly different (P > 0.05). In addition, larger eggs resulted in larger fry. The fry size produced by small broodstock size range and the large broodstock size was significantly different (P < 0.05). The survival rate of fry after starvation increased with increase in parent broodstock size. For larger eggs and fry production, broodstock of C. gariepinus, of average size of 500 – 1099 g should be selected for use in fish hatchery operation in Nigeria. Key Words: Broodstock, Egg, Larvae, Clarias gariepinus Journal of Aquatic Sciences Vol.19(1) 2004: 1-4

Influences of Freshwater and Marine Growth on the Egg Size–Egg Number Tradeoff in Coho and Chinook Salmon

How to partition a finite amount of energy into progeny is an important issue in evolutionary biology. Salmonids produce a small number of large eggs compared with other teleost fishes, and there are positive correlations between female size and both the size and number of eggs produced. We examined the temporal variation in reproductive investment (gonad mass, fecundity, and egg size) of coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha at the University of Washington hatchery over the last three to five decades. During this period, fish growth rates in freshwater and at sea varied greatly, allowing us to test the hypotheses that rapid early growth rate results in high fecundity and that hatchery populations evolve high fecundity over time. In the coho salmon, reductions in length, condition factor, and size-adjusted fecundity over the past decades combined to reduce overall average fecundity to only about half its former level. In Chinook salmon, age at maturity decreased as smolt size increased, so average size decreased over time but size at a given age did not decline. Reproductive investment (gonad size, corrected for body size) decreased for the coho salmon but not for the Chinook salmon. Egg size (adjusted for variation in fish size) did not vary with growth rate for either species or environment. Size-adjusted fecundity did not increase with increasing freshwater growth for either species, but it did increase with marine growth for the coho and age-3 Chinook salmon. These results contradict the prediction that females adjust egg size depending on the perceived quality of the juvenile habitat. Egg size is probably determined much later in life, corresponding to the number of remaining eggs and the energetic constraints at maturity. The results are also inconsistent with the hypothesis that hatchery populations will evolve small eggs and high fecundity as a result of a relaxed selection for large fry.

Use of Tilapia as Supplemental Forage for Channel Catfish Broodstock

Abstract The purpose of this study was to determine the effects of supplemental feeding with forage fish on the spawning success and egg quality of channel catfish Ictalurus punctatus. Channel catfish broodstock were maintained for 2 years on a diet of either commercial catfish feed with 32% protein or commercial catfish feed and live blue tilapia. Fish fed forage fish had significantly larger eggs and a higher gonadosomatic index prior to the second spawning season. They also spawned larger eggs, had a higher hatch rate, and produced more and larger fry than fish fed only commercial feed. During the second year of the study, growth rates and food conversion ratios were better over the winter months for channel catfish fed supplemental forage but worse over the summer months compared with fish fed only commercial feed. Over the two spawning seasons, broodstock fed forage fish produced an average of 9,221 sac fry/kg of females stocked in the spawning ponds. The addition of 10–15 kg/ha of blue tilapia to ch...

Evaluation of Decapsulated Artemia Cysts in Hatchery Diets for Channel Catfish Ictalurus punctatus Fry and Effects on Subsequent Fingerling Production

Abstract.— Two 10‐d hatchery growth trials were conducted to determine if differences in growth, body composition, and survival existed among catfish fry Ictalurus punctatus fed a diet of 100% catfish‐starter (CS) or CS in combination with decapsulated Artemia cysts (DAC) at 25%, 50%, or 75% of diet weight. A 120–d production trial was undertaken immediately following the first hatchery trial to evaluate the effects of diet on production characteristics (survival, length, weight, feed conversion ratio, and total yield) of fingerling catfish produced from hatchery‐raised fry. Fry fed diets containing DAC weighed 61–98% more (P &lt; 0.05) than fry fed only CS. The size differential of DAC‐fed fry was maintained through 120 d of growth in simulated nursery ponds (0.001‐ha earthen‐bottom pools). The increased growth of fry fed DAC might have been related to differences in dietary lipid content, amino acid composition, or digestibility of CS and DAC. Body weights of fingerlings produced under simulated production conditions from fry fed hatchery diets containing 50% and 75% DAC were 17% and 25% higher, respectively, 130 d post‐hatch, than fingerlings produced from fry fed only CS. In addition, the total yield of fingerlings produced from fry fed 75% DAC was 17% greater that that of fingerlings produced from fry fed only CS. The increased performance of fingerlings produced from DAC‐fed fry could have resulted from their larger size at stocking, since larger fry might be capable of capturing natural food organisms and ingesting prepared diets more effectively than smaller fish. CS‐DAC diet combinations could be used to increase weight gain of hatchery‐raised fry if the cost‐benefit ratio of adding DAC to the standard hatchery diet warrants its use.

Growth, Survival, and Migration Patterns of Juvenile Adfluvial Bonneville Cutthroat Trout in Tributaries of Strawberry Reservoir, Utah

Adfluvial Bonneville cutthroat trout Oncorhynchus clarki utah were introduced into Strawberry Reservoir after a rotenone treatment in 1990. Naturally reproduced fry either migrated to the reservoir immediately after emergence (migrants) or remained in the tributaries for 1–2 years (nonmigrants). In 1995, fry emerged from mid-August to early September. Migrants moved downstream almost exclusively between 2100 and 0300 hours. Migrants were always the same size as newly emerged fry, whereas the mean size of nonmigrant fry increased throughout the emergence period. Most fry followed the nonmigrant strategy. Nonmigrant fry grew from 0.12 g (26 mm) at emergence to an average 1.2 g (50 mm) by early November. Mean densities of nonmigrant fry in low-velocity microhabitats along the stream margins ranged from 5.5 to 11.0 fry/m2 during the 6 weeks after first emergence. Mean focal point velocity of nonmigrant fry in microhabitats was 3.3 cm/s (SD = 1.4, N = 42) and the mean focal point depth was 11.8 cm (SD = 6.5, N = 80). By late September, larger fry (>50 mm) shifted from the stream margins into the main channel. Growth and survival of migrants and nonmigrants were compared at low, ambient, and high fry densities in enclosure experiments to test whether migrants were inferior competitors in the stream. Growth and survival were similar for cohabiting migrants and nonmigrants within and among the three fry density treatments in the enclosure experiments. Growth was not affected by fry densities after 3 weeks; however, growth declined similarly for both migrant and nonmigrant fry in the high-density treatment compared with the low- and medium-density treatments after 6 weeks. Since no competitive differences were evident among the migrants and nonmigrants, emigration could be an innate response by some fraction of the population rather than the result of inferior competitors being forced downstream.

Predation risk breaks size-dependent dominance in juvenile coho salmon (Oncorhynchus kisutch) and provides growth opportunities for risk-prone individuals

Groups of coho salmon (Oncorhynchus kisutch) fry in stream tanks formed size-determined dominance hierarchies, which were upheld through aggressive interactions and led to smaller fish occupying inferior feeding positions. Under simulated predation risk, the frequency of agonistic interactions was reduced, but more intensive aggressive behaviours were performed. This allowed small fish to gain access to better feeding positions. The effect of the predation threat on coho behaviour seemed to extend across a riffle into a second pool that served as a refuge. Smaller fry that chose to be in the exposed pool had greater growth rates than those that mainly occupied the refuge, while large fry that exposed themselves to predation did not grow better than their risk-avoiding counterparts. Differences in risk taking and growth among small coho fry in this experiment may support reports for Atlantic salmon (Salmo salar) of a split into different life history trajectories. The observations suggest that the presence of predators creates opportunities for the expression of alternative behavioural strategies that are absent under size-dependent dominance hierarchies.

Test of size-specific mass selection for Nile tilapia, Oreochromis niloticus L., cage farming in the Philippines

One generation of mass selection based on the collimation procedure (early culling of large fry) was applied on Nile tilapia, Oreochromis niloticus L., in net cages set in Laguna de Bay, Philippines. The objective was to test the effectiveness of a low-cost, small-scale broodstock improvement procedure in this culture environment. Directional selection was performed in two steps after initial removal of large fry at 21 days. Selection of parents and testing of the offspring were also conducted in hapa net cages set up in Laguna de Bay. The selection resulted in a significant positive response of 3% relative to the control, which represents a projected 34% gain over 5 years in Laguna cage culture. The realized heritability is ≈16%.

Influence of brood size and offspring size on parental investment in a biparental cichlid fish,Neolamprologus moorii

Both males and females ofNeolamprologus moorii, a substrate-spawning cichlid fish in Lake Tanganyika, tend their eggs and fry. In this study, the influence of brood size and fry size on parental investment of this species was examined under natural conditions. Breeding parents intensively attacked fry-eating fishes that approached their broods. The attack rate by the parents against the approaching fry-eaters was positively correlated with brood size and negatively with fry size, but was much more strongly related to brood size. This suggests that the parental decision for brood defense appeared to be primarily determined by brood size. The reason for fry size being less important in the parental decision may be that even large fry have a low survival ability on their own under the high predation pressure in the study sites.

Ontogenetic Sensitivity of Channel Catfish to Ascorbic Acid Deficiency

Abstract Two distinct nutritional experiments were conducted sequentially with fry of channel catfish Ictalurus punctatus. Initial weight of fish was 0.030 ± 0.003 g in experiment 1 and 1.36 ± 0.03 g in experiment 2. In both experiments, fry were fed a semipurified, casein–gelatin-based diet containing no ascorbate supplement (AA-free) or a diet supplemented with 640 mg ascorbate/ kg as ascorbyl monophosphate (AP); fry used in experiment 2 had been given the AP-supplemented diet in experiment L Fish fed a diet devoid of vitamin C showed significantly reduced growth after 14 d in experiment 1 and 28 d in experiment 2. In experiment 1, fry fed starter feed lacking vitamin C showed significantly increased mortalities during the sixth through eighth weeks. At the same time, gross clinical signs of deficiency appeared, such as darker skin pigment, scoliosis, lordosis, and eroded fins. In experiment 2, larger fry did not show any mortality or external pathologies during the 54 d of the feeding study. The ascorb...

The Dilution Effect and Differential Predation Following Brood Adoption in Free‐ranging Convict Cichlids (Cichlasoma nigrofasciatum)

AbstractParental investment in unrelated offspring is potentially maladaptive but may be promoted by natural selection if the presence of foreign young enhances the survival of the parents' own young. We experimentally augmented broods of free‐ranging convict cichlids (Cichlasoma nigrofasciatum) to test whether survival of the adopting parents' young (fry) increases, in relation to that of control broods, after the addition of smaller foreign fry, and whether such an increase can be attributed to the effect of brood dilution acting alone or to a combination of brood dilution and the effect of differential predation on adopted young. Total fry survival did not differ between experimental (E) broods and control (C) broods, but E broods had significantly more large (host) fry after 5 days and 10 days than C broods did. In E broods, small (foreign) fry suffered higher rates of predation than large fry, indicating differential predation. In E broods starting at 7.0 and 7.5 mm standard length (SL), observed fry mortalities did not differ significantly from mortalities expected from the effect of brood dilution. However, E broods starting at 8.0 mm SL had significantly lower mortalities than expected, indicating that parents that adopt smaller foreign fry can increase the survival of their own fry by the combined effects of brood dilution and differential predation. Within E broods, growth of smaller foreign fry was significantly slower than that of larger host fry, suggesting that intra‐brood agonistic behaviour affects access to food for smaller fry. Therefore, increased predation and reduced growth are two negative effects that act on fry of donor parents.

Intraspecific brood adoption in convict cichlids : a mutual benefit

Convict cichlids (Cichlasoma nigrofasciatum) are biparental, substrate brooding cichlid fish which have extended care of their eggs, larvae (wrigglers) and free-swimming young (fry). Field observations indicate that intraspecific brood adoption of fry occurs frequently under natural conditions. Of 232 broods 29% contained foreign fry and of 232 broods 15% were identified as fry donors. Foreign fry were usually of similar size to or smaller than the host brood fry. Experimental fry transfers showed that parents accept foreign fry smaller than their own but immediately reject or eat foreign fry larger than their own. A predation experiment showed that within a mixed brood, smaller fry are eaten more often than larger fry. Thus, accepting foreign fry may benefit parents through the dilution effect and through a differential predation effect. In comparison with intact families, broods from which the male parent was removed were less likely to reach independence, had fewer fry surviving to independence, and had a greater probability of having some fry transferred to neighbouring broods. We propose that intraspecific brood adoption in convict cichlids is mutually beneficial to the adult donors and recipients.

Threespine stickleback aggregations create a potential predation refuge for sockeye salmon fry

Coho salmon (Oncorhynchus kisutch) frequently consume sockeye salmon (Oncorhynchus nerka) fry in Chignik Lake, Alaska, but have never been observed to consume threespine sticklebacks (Gasterosteus aculeatus), which are often closely associated with sockeye fry. Because coho salmon are visual predators and appear to avoid sticklebacks, a series of experiments was conducted in net pens to determine whether juvenile sockeye associated with threespine sticklebacks experienced less prédation than sockeye without sticklebacks and whether prey size affected prédation rates. Significantly fewer sockeye fry by coho were consumed in the pen containing 60 sticklebacks [Formula: see text] than in the 30-stickleback (4.7 fry/day) and 0-stickleback (4.4 fry/day) pens. An identical experiment with large, yearling sockeye (rather than sticklebacks) did not reveal a significant effect (p = 0.28), although there was a tendency for fewer large fry to be consumed when yearlings were abundant. A third experiment demonstrated predation rates on fry that were 45% lower in the presence of sticklebacks (1.2 fry/day) than in the presence of yearling sockeye (2.2 fry/day). Large sockeye fry (37–44 mm) consumed by coho declined steadily from about 36 to 29 to 22% of the total number of fry eaten as the number of sticklebacks or yearling sockeye increased from 0 to 30 to 60, respectively. These data suggest that the presence of threespine sticklebacks may reduce predation by coho on juvenile sockeye, especially those sockeye similar in size to sticklebacks.

Effects of Organic Enrichment on Zooplankton Abundance and Walleye Fry Growth and Survival in Artificial Rearing Ponds

ABSTRACT Cylindrical aluminum enclosures in an artificial rearing pond were used to examine the effect of organic enrichment with alfalfa pellets and fish predation on the abundance and size structure of cladocerans and the growth and survivorship of walleye (Stizostedion vitreum vitreum) fry. Organic enrichment had a stronger effect than walleye fry predation on cladoceran abundance. Increased cladoceran abundance was due to increased abundance of smaller individuals, suggesting organic enrichment stimulated cladoceran reproduction. Although fish predation did not influence total cladoceran abundance, it did appear to reduce the abundance of larger size classes of cladocerans (> 1.25 mm total length). Organic enrichment did not increase survival of walleye fry but did increase their average weight and condition, especially among larger fry.