Fry Stage Research Articles

Effects of formulations of the fungicide, pentachloronitrobenzene on early life stage development of the Japanese medaka (Oryzias latipes)

Quintozene is a fungicide containing the active ingredient, pentachloronitrobenzene (PCNB) that is used to control “snow mold” on golf courses in temperate regions of North America. In this study, quintozene and a formulation of quintozene widely used on golf courses, FFIITM were tested for toxicity to early life stages of the Japanese medaka, Oryzias latipes. For medaka exposed in static non-renewal assays to quintozene for 17d from the fertilized egg stage to yolk resorption at the fry stage, the LC50 for mortality was a nominal concentration of 707μgl−1 and the effective concentration for 50% hatch (i.e. EC50) was a nominal concentration of 71μgl−1. Eggs and fry showed developmental abnormalities, including ocular malformations and retarded development of the brain, notochord, organs and body segmentation, which were interpreted as teratogenic responses to exposure to PCNB. For medaka exposed to quintozene, the LOECs for abnormalities of the eye and all other developmental abnormalities were 750 and 100μgl−1, respectively. In medaka exposed to the FFIITM formulation, similar patterns of mortalities, reduced hatching success and developmental abnormalities were observed, but at higher test concentrations that were consistent with the proportion of quintozene in the formulation. For medaka exposed to the formulation, the LOECs for abnormalities of the eye and all other developmental abnormalities were 10000 and 1000μgl−1, respectively. Overall, these data indicate that studies should be conducted to assess the risk of exposure of early life stages of fish to quintozene in watersheds impacted by golf courses.

Threonine requirements for rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) at the fry stage are similar

In order to compare the threonine (Thr) requirement and retention efficiency of rainbow trout and Atlantic salmon, we conducted a feeding experiment with 11 diets. For both species, we studied the effects of increasing dietary L-Thr: 5, 6.25, 7.5, 8.75, 10, 11.25, 12.5, 13.75, 15, 16.25, 21.75 g/kg dry matter (DM), on protein gain, Thr gain and Thr retention efficiency. All diets were isonitrogenous (40% DM) and isoenergetic (22.4 MJ gross energy/kg DM). To maintain the same nitrogen (N) level, the decrease of Thr in the diets was compensated by an increase of a mixture of dispensable amino acids. The rainbow trout and Atlantic salmon fry mean initial body weight was of 1.8 and 0.8 g, respectively, and they were fed for 24 and 36 days, respectively. The daily growth coefficient (% day−1) was much higher for rainbow trout fry (2.5% day−1) than for Atlantic salmon fry (1.1% day−1). For the Thr deficient diets (Thr levels ≤10 g/kg DM), feed efficiency and protein productive value were higher in trout than in salmon fry, and they were mainly related to differences in voluntary feed intake. The Thr requirements for optimal Thr accretion (± SE) determined by the broken-line model were equivalent among species: 10.58±0.56 and 10.66±0.36 g/kg DM or 2.6±0.1 and 2.7±0.1 g Thr/16 g N (P=0.4) for trout and salmon fry, respectively. At marginal dietary Thr concentrations (≤10 g/kg DM), Thr accretion (mg/kg0.75 per day) was a linear function of Thr intake (mg/kg0.75 per day) for salmon and trout, but slopes were not significantly different (P=0.19). The slope of the single line estimation (r2=0.94) gave an estimate of the Thr retention efficiency above maintenance (±SE) for both species (0.79±0.04). Additionally, the relationship between protein gain and Thr intake showed that trout and salmon required an intake of 70 and 62 mg of Thr, respectively, to deposit 1 g of body protein (P=0.21). Application of a simple factorial method to our data gave the same relative Thr requirement value as the one determined empirically. In conclusion, this study showed that neither the dietary Thr requirement nor the Thr retention efficiency above maintenance was influenced by fish species although they have such different growth rates at the fry stage.

River Restoration Effects on Steelhead Populations in the Manistee River, Michigan: Analysis Using an Individual‐Based Model

AbstractThe Manistee River, Michigan, watershed includes two dams as well as residential and agricultural development, and the river itself contains a sizeable population of steelhead Oncorhynchus mykiss that supports a valuable recreational fishery. Restoration of the Manistee River and its flow regime may improve steelhead habitat and the fishery. We developed an individual‐based model of steelhead in the Manistee River to assess the population effects of changes in the number of spawners, water discharge from Tippy Dam, and water temperature. The model follows steelhead from spring spawning to the end of the growing season in early fall and depicts the river environment as a series of cells that vary in dimension, water velocity, and substrate. Simulated water discharge, temperature, and prey availability changed daily based on observations from Tippy Dam. Empirically based models describe individual steelhead fry and parr foraging and growth. In the model, steelhead select habitats and maximize individual fitness while accounting for dominance and the availability of feeding territories. We calibrated the model to replicate fish growth, mortality, and population size. Simulation experiments manipulated the number of spawning females, water discharge, and water temperature. The results suggest that Manistee River steelhead incur density limitations in the fry and parr stages and that water discharge and temperature changes affect the number and biomass of parr. Increasing river discharge negatively affected parr numbers and weight. Decreasing maximum midsummer temperature increased parr numbers and weight when the change was large, but otherwise had little effect. These results indicate that restoration of the natural flow regime in the Manistee River will probably increase the quality of the habitat for steelhead but that density limitations in the fry and parr stages may ultimately limit population growth.

Juvenile bottlenecks and salinity shape grey mullet assemblages in Mediterranean estuaries

Previous research has suggested that competitive bottlenecks may exist for the Mediterranean grey mullets (Osteichthyes, Mugilidae) at the fry stage with the exotic Cyprinus carpio (Osteichthyes, Cyprinidae) playing a central role. As a consequence, the structure of grey mullet assemblages at later stages is thought to reflect previous competition as well as differences in osmoregulatory skills. This paper tests that hypothesis by examining four predictions about the relative abundance of five grey mullet species in 42 Western Mediterranean estuary sites from three areas (Aiguamolls de l'Empordà, Ebro Delta and Minorca) differing in the salinity level and occurrence of C. carpio. Field data confirmed the predictions as: (1) Liza aurata and Mugil cephalus were scarce everywhere and never dominated the assemblage; (2) Liza saliens dominated the assemblage where the salinity level was higher than 13; (3) Liza ramado always dominated the assemblage where the salinity level was lower than 13 and C. carpio was present; and (4) Chelon labrosus dominated the assemblage only where the salinity level was lower than 13 and C. carpio was absent. The catch per unit effort of C. labrosus of any size was smaller in the presence of C. carpio than where it had not been introduced, which is in agreement with the juvenile competitive bottleneck hypothesis. Discriminant analysis confirmed that the assemblage structure was linked to the salinity level and the occurrence of C. carpio for both early juveniles and late juveniles as well as adults. The data reported here reveal that the structure of grey mullet assemblages inhabiting Mediterranean estuaries is determined by salinity and competitive interactions at the fry stage.

Effects of fish farm effluents on egg‐to‐fry development and survival of brown trout in artificial redds

Egg‐to‐fry development and survival of brown trout Salmo trutta were compared in two rivers of the Pyrenean piedmont, the Nive d’Arnéguy, with few human activities, and the Nive des Aldudes, with many anthropogenic activities including 11 fish farms and two sewage treatment plants (STPs). Survival was estimated between spawning (early December) and emergence time (early March) by means of capsules, 7 cm3 in volume, filled with green eggs then inserted into the gravel of artificial redds at spawning sites. In the Nive des Aldudes, three sets of conditions were studied: a fish farm near the springs, a fish farm and an STP in a village, and a series of fish farms and an STP in a village. In each situation, two artificial redds were created upstream and two others downstream from the fish farms. In the Nive d’Arnéguy, four sites were equipped: each of the two downstream sites with two artificial redds, and the two upstream sites with one redd. Substratum characteristics (proportion of fine particles) and the quality of surface and interstitial water (oxygen content, ammonia and nitrite nitrogen) were periodically measured. There was no redd substratum difference between sites upstream and downstream of fish farms. Survival to fry emergence was higher in the Nive d’Arnéguy (63·5%) than in the Nive des Aldudes (47·7%). In this latter river, the nitrogen released from the STPs was 0·5% that from fish farms. Fish farming impaired survival close to fish farm effluents (31·6%), as compared to survival upstream (63·6%), and induced a development delay during the yolk‐sac fry stage. These differences were mainly linked to a drop in the dissolved oxygen content in interstitial water induced by the nitrogen flow in surface and interstitial waters.

THE PRODUCTIVITY OF NILE TILAPIA, OREOCHROMISNILOTICUS (L.) REARED UNDER DIFFERENT BROODSTOCK DENSITIES AND PHOTOPERIODS IN A RECYCLING WATER SYSTEM

The effect of three brood fish stocking densities (4, 8 and 12 fish / m2) combined with three photoperiods (12, 15 and 18 hours/day) on the fry production of the Nile tilapia, Oreochromis niloticus (L.), were evaluated in a recycling water system. Treatments were arranged according to a 3x3 factorial design with three replicates giving a total of 27 spawning fiberglass tanks. Males and females with mean body weights of 160.3 and 112.0 g, respectively, were stocked at a male: female ratio of 1:3 in all tanks, and the experiment lasted for 120 days. The results showed thai breeders stocked at the lowest stocking density (4 fish / m2) combined with the longest photoperiod (18 hours/day) had significantly higher (P<0.05) mean values for total fiy production, fry / kg female /day, fry / female /day, fry / m 2 / day, spawning rate and hatching rate than at 8 and 12 fish/nr broodstock densities exposed to the same photoperiod. Moreover, the productivity parameters of tilapia decreased in descending order with the medium and short photoperiods (15 and 12 hours/day, respectively) for all densities. The maximum percentage of yolk-sac and swim-up fry stages were obtained at the lowest stocking density combined with, the longest photoperiod. These findings are discussed to achieve optimum reproductive performance of Nile tilapia broodstock for fry production management.

A Comparative Study on the Growth, Feed Conversion and Production of Fry of Improved and Non-improved Strains of the Nile Tilapia Oreochromis niloticus

Two experiments were conducted consecutively to evaluate and compare the mean weight (MWT), daily growth rate (DGR), feed conversion ratio (FCR), survival and production rate (PR) in the non-improved strain (NS) of the Nile tilapia, Oreochromis niloticus (Cichlidae) with those in the Genetically Improved Farmed Tilapia (GIFT) strain and the FaST selected tilapia (FaST), from the swim-up fry stage to fish weight of 1.0 g (Experiment 1) and from fish weight of 1.0 to 20 g (Experiment 2). In both experiments, results showed the GIFT and FaST strains to have significantly higher MWT, faster DGR, lower FCR and higher PR than those of the NS. Unlike in Experiment 1, survival rates did not differ significantly among the three strains. In Experiment 1, the improvements in the FaST for the MWT, DGR and PR over those for the NS were 77.9, 72.9 and 33.6%, respectively. In Experiment 2, the improvements for the same parameters were 58.7, 57.8 and 54.5%, respectively. These results indicate the advantage and potential of culturing the FaST or the GIFT strain in Kuwait for improving the production of fresh tilapia, reducing the production cost and increasing the profitability of tilapia farms.

Gene–environment interactions influence ecological consequences of transgenic animals

Production of transgenic animals has raised concern regarding their potential ecological impact should they escape or be released to the natural environment. This concern has arisen mainly from research on laboratory-reared animals and theoretical modeling exercises. In this study, we used biocontained naturalized stream environments and conventional hatchery environments to show that differences in phenotype between transgenic and wild genotypes depend on rearing conditions and, critically, that such genotype-by-environment interactions may influence subsequent ecological effects in nature. Genetically wild and growth hormone transgenic coho salmon (Oncorhynchus kisutch) were reared from the fry stage under either standard hatchery conditions or under naturalized stream conditions. When reared under standard hatchery conditions, the transgenic fish grew almost three times longer than wild conspecifics and had (under simulated natural conditions) stronger predation effects on prey than wild genotypes (even after compensation for size differences). In contrast, when fish were reared under naturalized stream conditions, transgenic fish were only 20% longer than the wild fish, and the magnitude of difference in relative predation effects was much reduced. These data show that genotype-by-environment interactions can influence the relative phenotype of transgenic and wild-type organisms and that extrapolations of ecological consequences from phenotypes developed in the unnatural laboratory environment may lead to an overestimation or underestimation of ecological risk. Thus, for transgenic organisms that may not be released to nature, the establishment of a range of highly naturalized environments will be critical for acquiring reliable experimental data to be used in risk assessments.

Molecular cloning, characterization and expression analysis of natural resistance associated macrophage protein (Nramp) cDNA from turbot ( Scophthalmus maximus)

Nramp (natural resistance associated macrophage protein) has been identified as one of the major candidate genes for controlling natural resistance and/or susceptibility to intracellular pathogens in vertebrates. However, few reports are available about the structure and function of Nramp in teleost. We have recently isolated the cDNA encoding Nramp from turbot ( Scophthalmus maximus). The full-length cDNA of the Nramp is 2584 bp in length, including 69 bp 5′ terminal UTR, 850 bp 3′ terminal UTR and 1665 bp open reading frame for a protein with 554 amino acid residues (Genbank accession number: DQ263240). Comparison of amino acid sequence indicated that turbot Nramp consists of 12 transmembrane regions (TM) domains. A consensus transport motif (CTM) containing 20 residues was observed between transmembrane domains 8 and 9. The deduced amino acid sequence of turbot Nramp exhibited between 60 and 92% homology with 13 other vertebrate Nramp sequences. Nramp transcripts were found to be highly abundant in head kidney, kidney and spleen, abundant in intestine and gill, less abundant in liver, brain, heart and gonad, least in muscle and skin. The level of Nramp mRNA in embryos gradually increases during embryogenesis from blastula stage to fry stage. Challenge of turbot with pathogenic bacteria, Vibrio anguillarum, elevated Nramp mRNA levels in liver and spleen. The Nramp transcripts were detected in turbot embryonic cell line (TEC). Challenge of the TEC cell cultures with pathogenic bacteria, V. anguillarum, significantly elevated Nramp mRNA levels in TEC cell cultures.

Catecholaminergic regulation of motor activity of embryos of the Atlantic salmon Salmo salar and development of stressogenic reactivity in the formation of the hypophyseo-interrenal axis in the postembryonal period

Dynamics of catecholamines (CA) and of cortisole (F) in the embryonic and early postembryonic periods of life of the Salmo salar was investigated in relation to the level of motor activity of embryos and the stressogenic response of fish juveniles and at the modification of the functional activity of the CA-system by pharmacological influences. In the embryonic period, the injections Droxydopa, a precursor of norepinephrine (NE), increased the level of inactivation of the maternal F from the yolk sac at the background of greater motor activity. Vice versa, the injections of 6-hydroxidopamine drastically decreased its inactivation and the level of motor activity. Labetalol, an antagonist of α-and β-adrenergic receptors, did not influence the intensity of inactivation of F but significantly decreased the motor activity of embryos. The hormonal response to acute stress was observed only at the end of prelarval development. At larval stages of development, the response at chronic stress was recorded and the flow was the stressor. The level of NE decreased at the background of the increase in the concentration of epinephrine (E) and F. Injection of aminoglutethimide to juveniles significantly decreased the level of F but clearly increased the level of E. Injections of aminoglutethimide and Droxydopa in the postembryonic period in the case of stress modified the functional activity of CA-ergic and their own steroid system. Aminoglutethimide decreased the temporal stability of juveniles to the flow to 30% by injections of Droxydopa, and vice versa, increased stability to 27%. The results of this and previous studies suggest that the integration of particular links of the hypothalamo-hypophyseo-interrenal axis into the general interconnected system occurs at the end of the larval stage—the beginning of the fry stage of development. Problems of organization of stressogenic response under the influence of hormonal CA-ergic and steroid links are discussed.

Molecular identification and expression analysis of the natural killer cell enhancing factor (NKEF) gene from turbot ( Scophthalmus maximus)

Natural killer cell enhancing factor (NKEF) belongs to the newly defined peroxiredoxin (Prx) family. It was originally isolated from human red blood cells. It has the ability to enhance the cytotoxic activity of natural killer cells, and appears most effective in the protection of DNA and protein against oxidative damage, chemotherapy agents, and inflammation-induced monocyte adhesion. However, few reports are available about the structure and function of NKEF in lower vertebrates such as teleosts. We have recently isolated a cDNA encoding NKEF from turbot ( Scophthalmus maximus). The cDNAs of NKEF were cloned from turbot spleen cDNA library. The 904 bp full-length cDNA of the NKEF was obtained by RACE and consisted of 122 bp 5′ terminal UTR, 591 bp encoding region and 191 bp 3′ terminal UTR. The 591 bp open reading frame was found to code for a protein with 197 amino acid residues. The deduced amino acid sequence of turbot had 85.3%, 81.7%, 81.2%, 80.7%, 80.7%, 79.2%, 78.2%, 77.7%, 77.7%, 77.2% and 58.2% identity with that of zebrafish, channel catfish, flounder, Tetraodon nigroviridis, rainbow trout and mouse Prx2-1, human NKEF-A, carp and rat TSA, human NKEF-B and yeast TSA, respectively. RT-PCR indicated that NKEF transcripts were abundant in the head kidney, spleen and liver, less abundant in the kidney and intestine, and least in gill, muscle and heart. The level of NKEF mRNA in embryos gradually increases during embryogenesis from two cell stage to fry stage. Challenge of turbot with pathogenic bacteria Vibrio anguillarum, significantly elevated NKEF mRNA levels in the liver and spleen in a time-dependent fashion. The NKEF transcripts were detected in turbot embryonic cell line (TEC). Challenge of the TEC cell cultures with pathogenic bacteria, V. anguillarum, significantly elevated NKEF mRNA levels in TEC cell cultures 48 h after infection.

Body size-related differences in the inhibition of brain acetylcholinesterase activity in juvenile Nile tilapia ( Oreochromis niloticus) by chlorpyrifos and carbosulfan

Influence of body size on inhibition of brain acetylcholinesterase (AChE) activity of juvenile Nile tilapia, Oreochromis niloticus by chlorpyrifos and carbosulfan was investigated concerning its potential use in the biomonitoring of anticholinesterase pesticides in tropical water bodies. Three size groups of fish (fry: 3–4 cm, fingerlings: 6–8 cm, sub-adults: 10–12 cm in total length) were exposed to a series of concentrations of chlorpyrifos (0.5–12 μg L −1) or carbosulfan (1–10 μg L −1), and concentration–response for inhibition and recovery of the AChE enzyme was evaluated in comparison to the controls at different time points, 2, 6, 10, and 14 d. The AChE activities of the control fish followed the order of decreasing activity, fry>fingerlings>sub-adults. AChE activities of the fry were nearly 2-fold higher than that of the sub-adults. Following 48 h of pesticide exposure, the AChE activity of the three size groups of fish decreased significantly in comparison to the respective controls in a concentration-dependent manner. The activity was greatly inhibited in the fry (39–85%) compared to sub-adults (18–47%) exposed to the most of the similar concentrations of the pesticides. Median effective in vivo inhibition concentrations (48 h IC 50) of chlorpyrifos for fry, fingerlings, and sub-adult stages were 0.53, 0.75, and 3.86 μg L −1, respectively, whereas the corresponding values for carbosulfan were 3.37, 7.02, and 8.72 μg L −1. When fish were maintained in the initial pesticide medium for 14 days, AChE activity restored gradually depending on the initial pesticide exposure concentration and the size group of the fish. Results indicate that brain AChE of Nile tilapia is a promising biomarker for assessment of anticholinesterase pesticide contaminations in water. However, body size of Nile tilapia should be taken into account when using this biomarker in biomonitoring programmes.

Fatty acid composition of Oncorhynchus mykiss during embryogenesis and other developmental stages

Fatty acid compositions of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) was determined during embryogenesis, yolk-sac fry, swim up fry and fry stages. Embryonic and yolk-sac development of fertilized eggs were followed until fry weighed 25 g and samples were taken from each stage to analyse fatty acid composition. Analyses of fatty acid composition were performed by gas chromatography mass spectrometry. Throughout all the developmental stages of O. mykiss important changes, such as an increase in the percentage of 18:2, 18:3 and 20:5 and as a decrease in the percentage of 14:0, 16:2, 20:0, 20:2, 20:3, 20:4 and 22:0 were observed in the amounts of fatty acid of developing eggs. During transition from the embryonic to the yolk-sac stage, an important increase in 20:0, 20:3, 20:5, 22:0 and a decrease in 18:3, 22:1 was determined between 45-day old embryo and yolk-sac fry. During transition from the 43 day yolk-sac stage to swim up stage, a decrease in the percentage of 18:0, 20:2 and an increase in the percentage of 14:0, 16:2, 18:2, 18:3 was seen. In all the observed stages, no qualitative but significant quantitative variations were determined in the fatty acid composition of O. mykiss. It may be concluded that 14:0, 16:0, 16:1, 18:0, 18:1 18, 20 and 22 polyunsaturated fatty acids are necessary for normal development of O. mykiss during their life stages.

Effects of expeller‐pressed/physically refined soybean oil on frying oil stability and flavor of french‐fried potatoes

AbstractTo determine effects of expeller pressing/physical refining of soybean oil (SBO) on frying, studies were conducted with expeller‐pressed, physically refined, bleached, deodorized SBO (EPSBO); hexane‐extracted, refined, bleached, deodorized SBO+TBHQ; and hydrogenated SBO (HSBO). Oils contained citric acid and dimethylpolysiloxane and were used for 35 h of frying french‐fried potatoes. Polar compound levels in EPSBO were similar to SBO+TBHQ or HSBO. Flavor quality of potatoes was evaluated by trained, experienced, analytical sensory panelists. In early frying stages, potatoes fried in EPSBO had significantly lower intensities of fishiness than potatoes fried in SBO+TBHQ. Potatoes fried in HSBO were described as “hydrogenated”. Because of differences in flavor intensities and types, potatoes prepared in EPSBO had significantly better quality scores than those fried in SBO+TBHQ or HSBO during the first 15 h of frying. During later stages (25 and 35 h), potatoes fried in EPSBO had significantly better quality scores than potatoes fried in HSBO. Variations in minor oil constituents may partly explain these differences. EPSBO had less total tocopherols and phytosterols than did SBO at 0‐time. During frying, TBHQ in SBO and Maillard reaction products in EPSBO probably inhibited tocopherol loss and therefore improved quality.

Dynamics of cortisol and the development of the glucocorticoid function in the early ontogenesis of Atlantic salmon Salmo salar

The dynamics of cortisol were studied during the embryonic and early postembryonic development of Atlantic salmon Salmo salar (in brood obtained from the same pair of spawners, but with differing hatching dates). The initial level of maternal cortisol in the eggs after fertilization comprised of 25.6 ± 2.2 ng/g, and decreased continuously in the development process to 1.1 ± 0.2 ng/g by the 95th day after fertilization (t1) or the 18th day after hatching (t2). The first increase in the concentration of endogenous cortisol to 6.1 ± 1.2 ng/g was recorded at t2 = 24 days. Then the level of cortisol increased constantly and reached 32.8 ng/g by t1 = 149 (t2 = 72). A comparison of the hormone dynamics in two offspring groups from the same pare of spawners, differing in the longevity of embryogenesis, demonstrated that the level of cortisol increased after hatching more intensely in fishes with shorter embryogenesis. An injection of DL-aminoglutethimide, a compound preventing the synthesis of cortisol, significantly decreased the concentration of cortisol for the first time at the day of t1 = 101 (t2 = 24), i.e. at the first moment of the increase of endogenous cortisol. The effect from the adrenaline injection as a stress hormone was observed only at the day of t1 = 149 (t2 = 72), i.e., during the transition to the fry stages of development. Problems concerning when steroidogenesis begins, of the formation of the hypothalamic-hypophyseal-interrenal axis as a single hormone-competent ensemble, and of the development the stressed response in salmon juveniles are discussed.

Predicting mechanical properties of fried chicken nuggets using image processing and neural network techniques

Typical approaches for measuring mechanical properties of fried food products are mostly destructive techniques. In this study, a non-destructive, image-based method was evaluated for predicting mechanical properties of fried, breaded chicken nuggets. The textural parameters of interest, namely maximum load, energy to break point, and toughness of fried chicken nuggets were measured. Values of the parameters changed over frying time. Images of the chicken nuggets were collected at different frying stages and five image texture indices were extracted using co-occurrence matrix. A multiple-layer feed-forward neural network was established to predict the three mechanical parameters. The correlation coefficients of the predicted results with those from mechanical tests were above 0.84.

Genetic Analysis of Wild Lake Trout Embryos Recovered from Lake Michigan

AbstractThe Mid‐Lake Reef Complex (MLRC) is a large area of deep reefs that separate the two main basins of Lake Michigan. In an attempt to evaluate which of several strains of lake trout Salvelinus namaycush stocked in Lake Michigan are actively spawning at the MLRC, eggs that had been deposited by spawning lake trout were collected at three sites on East Reef. These eggs were incubated and shown to be viable and capable of developing to the emergent fry stage. The samples were genotyped at four microsatellite loci, and a proportional admixture analysis was performed to estimate the genetic contribution of the four predominant lake trout hatchery strains used to stock the MLRC. These estimates were then compared with the abundance of each strain stocked since 1985. The point admixture estimates indicated unequal spawning success among strains in the wild. Specifically, the Seneca Lake strain appeared to be the most successful, while the Lewis Lake strain was the least successful and may not be spawning in the wild. The implications for conservation management are also discussed.

Estimates of egg deposition and effects of lake trout (Salvelinus namaycush) egg predators in three regions of the Great Lakes

Excessive mortality from spawning through the first year of life is likely responsible for recruitment failures in many lake trout (Salvelinus namaycush) populations. We evaluated relationships between interstitial predator species and lake trout egg deposition in three regions of the Great Lakes. The introduced crayfish Orconectes rusticus dominated the nearshore zone in northern Lake Michigan, whereas other sites in Lake Michigan and Parry Sound were dominated by native Orconectes propinquus. In Lake Champlain, sculpin (Cottus spp.) were the most common interstitial predator, yet densities were comparable with those in Lake Michigan. Predator densities in Lake Michigan (mean ± standard error = 15.5 ± 0.4 predators·m–2) were twice those in Lake Champlain or Parry Sound (6 ± 1 predators·m–2). Densities of eggs were higher in Lake Champlain (2994.1 ± 398.3 eggs·m–2) and Parry Sound (454.7 ± 36.3) than in Lake Michigan (7.5 ± 1.3; Kruskal-Wallis, P ≤ 0.05). Ratios of eggs to predator provide simple measures of the effectiveness of lake trout rehabilitation efforts. The average ratio calculated from 10 successful spawning locations is 190 eggs·predator–1·m–2. Ratios may help establish target egg densities for restoration efforts and the concentration of spawning adults required to allow survival to the fry stage.

SELECTION ON INCREASED INTRINSIC GROWTH RATES IN COHO SALMON, ONCORHYNCHUS KISUTCH

Substantial evidence from the animal kingdom shows that there is a trade-off between benefits and costs associated with rapid somatic growth. One would therefore expect growth rates under natural conditions to be close to an evolutionary optimum. Nevertheless, natural selection in many salmonid species appears to be toward larger size and earlier emergence from spawning redds, indicating a potential for increased growth rate to evolve. We tested how selection for genetic variants (growth hormone transgenic coho salmon, Oncorhynchus kisutch, with more than doubled daily growth rate potential relative to wild genotypes) depended on predator timing and food abundance during the early period of life (fry stage). In artificial redds, fry of the fast-growing genotypes showed a highly significant developmental shift, emerging from gravel nests approximately two weeks sooner, but with an 18.6% reduced survival, relative to wild-genotype fry. In seminatural streams, fry of the fast-growing genotypes suffered higher predation than those of wild genotypes when predators were present at the time of fry emergence, but this difference was less pronounced when food was scarce. In streams where predators were introduced after emergence, fry survived equally well regardless of food availability. Surviving fry grew faster in habitats provided with more food, and fast-growing genotypes also grew faster than wild genotypes when predators arrived late and food was abundant. Fewer fish migrated downstream past a waterfall when food availability was high and in the presence of predators, and wild-genotype fry were more likely to migrate than fry of the fast-growing genotypes. After being returned to the experimental streams after migration, fast-growing genotypes survived equally well as those of the same genotypes that did not migrate, whereas migrating wild genotypes experienced higher mortality relative to those of the same genotypes that did not migrate. Comparisons of growth rates between siblings retained under hatchery conditions and those from habitats with the fastest growth in the experimental stream revealed that growth rates were similar for wild genotypes in both environments, whereas the fast-growing genotypes in the streams only realized 90% of their growth potential. The present study has shown that a major shift in developmental timing can alter critical early stages affecting survival and can have a significant effect on fitness. Furthermore, ecological conditions such as food abundance and predation pressure can strongly influence the potential for fast-growing variants to survive under natural conditions. The large-scale removal of many predatory species around the world may augment the evolution of increased intrinsic growth rates in some taxa.

Production of Triploid Lake Trout by Means of Pressure Treatment

AbstractTo induce triploidy in lake trout Salvelinus namaycush, we treated a production‐sized group at Story State Fish Hatchery, Wyoming, with 65,500 kPa at 300 degree‐minutes (°C·min) for 5 min and investigated four different pressure treatments (62,053 kPa at 300°C·min for 5 min; 65,500 kPa at 200, 300, or 400°C·min for 5 min) at Saratoga National Fish Hatchery, Wyoming. For the production group, eggs hatched and survived at a higher rate when held in chilled water (10.6°C) than ambient water (11.5°C). For the experimental groups, mean survival of pressure‐treated groups to the eyed egg, hatching, and feeding fry stages was at least 15% lower than that of the control group. However, due to high variability, there was no statistical difference in survival among the experimental groups. All fry (n = 178) sampled from the four experimental treatments and the single production group were triploid.