An Examination of Utilizing External Measures to Identify Sexually Maturing Female American Eels, Anguilla Rostrata, in the St. Lawrence River

It is well established that Anguillid eels undergo a complex suite of morphological and physiological changes during their transformation from resident, yellow-phase juveniles to actively migrating silver-phase eels. While it has been shown that some morphological measures can be used successfully to identify sexually maturing European eels, Anguilla anguilla, as well as Australian short fin, Anguilla australis, and long fin, Anguilla dieffenbachii eels, this relationship has never been quantitatively assessed for American eels, Anguilla rostrata. American eels of varying sexual development were collected from three locations on the St. Lawrence River: Lake St. Lawrence, Quebec City and Kamouraska. Sexual development of each eel was assessed with gonadosomatic index (GSI), oocyte diameter and degree of oocyte development. Morphological measures of total length, weight, head width, pectoral fin length and vertical and horizontal eye diameters were obtained from each fish. We used this data to test two hypotheses: (i) resident yellow phase eels, suspected migrants and known migrants are morphologically indistinguishable; and (ii) if differences exist, they cannot be used to reliably predict gonadal development or migratory status. Univariate analysis (ANOVA and ANCOVA) indicated that there were highly significant differences in all of the measured parameters and thus we were able to reject the first hypothesis. However, we failed to reject the second hypothesis as the high degree of overlap between groups eliminated the ability of any single measure to differentiate between resident and migratory eels. A multivariate discriminant model was developed that could classify only 72–80% of the eels correctly based on their morphological characters. While morphological measures may have some potential as a rapid, cost-effective method of pre-screening individual eels, morphological measures should not be considered a definitive indicator of sexual maturity or migratory status for female American eels in the Upper St. Lawrence River.     

Reproductive biology of the conger eel from the south coast of Brittany, France and comparison with the Europe eel

The gonadosomatic indices (I_G) of female conger eel Conger conger , aged between 2 and 11 years postmetamorphosis, ranged between 0·04 and 4·78 and were correlated with both age and body length. Microscopical examination of the gonads showed immature ovaries at two main stages of oocyte development, pre-vitellogenic oocytes for I_G < 1, and oocytes at an early vitellogenic stage (lipid vesicle stage) for I_G>1. The immaturity of the conger eels sampled in Concarneau Bay indicates that this species probably spawns in deeper oceanic waters. Radioimmunoassays (RIA) of sex steroids gave low serum levels of oestradiol and of 11-ketotestosterone, but higher levels of testosterone correlated with increase in I_G. Immunoenzymatic assay (ELISA) indicated low serum levels of vitellogenin (VtG), which were significantly correlated with I_G. The pre-vitellogenic and early vitellogenic stages observed in the coastal C. conger were similar to the oocyte stages found in the European eel Anguilla anguilla , at the yellow and silver phases of its life cycle respectively. However, other morpho-functional changes, associated with silvering in Anguilla species, such as the increase in ocular index, and regression of the digestive tract, did not occur at the early vitellogenic stage in conger eels.     

Influence of plasma lipid changes in response to 17β-oestradiol stimulation on plasma growth hormone, somatostatin, and thyroid hormone levels in immature rainbow trout

Plasma total lipids were significantly higher in 17β-oestradiol(E₂)-treated immature rainbow trout Oncorhynchus mykiss at week 4 after implantation, due to increases in polar and neutral lipids. The lipid classes responding were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, sterols and sterol esters, in a proportion that approximately reflected the increase in plasma vitellogenin (VtG) levels as measured by a non-competitive enzyme-linked immunosorbent assay (ELISA). Plasma non-esterified fatty acids and triacylglycerol were not affected by E₂ treatment. Plasma growth hormone GH levels were increased, and plasma somatostatin-14 (SRIF) levels decreased in E₂-treated fish, responses which could be secondary to elevated plasma lipid (VtG) content, although a direct E₂ action on somatotroph function is possible. Plasma T₄ concentrations were not affected by E₂ treatment, but plasma T₃ concentrations were significantly lower than in controls 1 week after implantation when plasma E₂ concentrations were the highest; this is in support of the hypothesis that E₂ has a suppressive action on T₃ production.     

Anguilla rostrata glass eel migration and recruitment in the estuary and Gulf of St Lawrence

This study describes catches of Anguilla rostrata glass eels and associated oceanographic conditions in the St Lawrence Estuary and Gulf. Ichthyoplankton survey data suggest that they enter the Gulf primarily in May, migrate at the surface at night, and disperse broadly once they have passed Cabot Strait. They arrive in estuaries beginning at about mid-June and through the month of July. Migration extends west up to Québec City, in the freshwater zone of the St Lawrence Estuary, 1000 km west of Cabot Strait. Anguilla rostrata glass eels travel between Cabot Strait and receiving estuaries at a straight-line ground speed of c. 10–15 km day⁻¹. Catches of fish per unit effort in estuaries in the St Lawrence system are much lower than those reported for the Atlantic coast of Canada. Low abundance of A. rostrata glass eels in the St Lawrence system may be due to cold surface temperatures during the migration period which decrease swimming capacity, long distances from the spawning ground to Cabot Strait and from Cabot Strait to the destination waters (especially the St Lawrence River), complex circulation patterns, and hypoxic conditions in bottom waters of the Laurentian Channel and the St Lawrence Estuary.     

Plasma non-esterified fatty acid profiles in wild Atlantic salmon during their freshwater migration and spawning

Total plasma non-esterified fatty acid (NEFA) levels increased significantly in adult Atlantic salmon during the first months of their upstream migration and spawning in the Exploits River, Newfoundland, Canada. The highest levels occurred in May and were 5467±270·43 nmol ml⁻¹ for females and 4617±334·70 nmol ml⁻¹ for males. Significantly higher levels were maintained by females compared with males for most of the upstream migration. Between August and October, total plasma NEFA levels declined by 61% in females but only 23% in males. The decline in plasma monounsaturated and polyunsaturated fatty acid levels accounted for 74% of the loss of NEFAs in females. Specific plasma NEFAs such as 16: 0 (palmitic), 16: 1 (palmitoleic), 18: 1n9 (oleic) and 20: 5n3 (eicosapentaenoic acid) differed significantly between males and females during migration and spawning. The mean gonadosomatic index ( I _G) values of females in May and just prior to spawning were 0·37±0·01 and 10·25±0·32, respectively. The rapid decline in the plasma NEFA content of females coincided with the largest increase in their I _G (1·85±0·02–10·25±0·32). Corresponding I _G values for males were 0·34±0·01 in May and 3·33±0·78 prior to spawning. Plasma NEFA levels of spent salmon did not differ between sexes and were significantly lower than those of salmon preparing to spawn.     

Lunar synchronization of testicular development and plasma steroid hormone profiles in the golden rabbitfish

Weekly changes in the gonadosomatic index (I_G) of male golden rabbitfish Siganus guttatus showed two peaks corresponding with the new moons in June and July. The testes developed synchronously toward the first lunar quarter in June and July. After the second spawning, the sperm duct and the seminiferous tubules were occupied by residual spermatozoa and spermatogonia, respectively. Weekly changes of plasma testosterone, 11-ketotestosterone and 17,20β-dihydroxy-4-pregnen-3-one coincided with those of testicular activity. They reached their peaks 1 week before spawning coinciding with the peaks of I_G and testicular development. These cyclical changes in plasma steroid hormones suggest that lunar periodicity is a major factor that synchronizes testicular activity of S. guttatus .     

Dose-related effects of 17βoestradiol (E2) on liver weight, plasma E2, protein, calcium and thyroid hormone levels, and measurement of the binding of thyroid hormones to vitellogenin in rainbow trout, Salmo gairdneri Richardson

Administration of 17β-oestradiol (E₂) to rainbow trout, in the form of hydrogenated coconut oil implants produced a stable, long-term elevation in plasma E₂ levels. The elevation was doserelated (over the range 1–10mg kg-¹ body weight) both 4 and 8 weeks after implantation. Dose-related increases were also observed with respect to liver weight-body weight ratios and plasma protein levels. Plasma T₃ and total calcium levels were depressed and elevated, respectively, by E₂ treatment but the responses were not linearly related to the dose of E₂ administered; there was no significant effect of E₂ on plasma T₄ levels.
E₂ induced a shift in the binding of T₃ to plasma proteins, with T₃ binding to smaller molecular weight proteins; neither T₄ nor T₃ bound to vitellogenin which was present at high levels in the plasma of E₂-treated fish.     

Some morphometric and biochemical features of ready-to-migrate silver and pre-migratory yellow stages of the shortfin eel of south-eastern Australian waters

The mean total length ( L _T), mass and age of ready to migrate female silver shortfin eels Anguilla australis from the Hopkins River estuary and the mouth of the Merri River in south-eastern Australia, were 83·2 ± 1·2 cm, 1051 ± 51 g, and 17·2 ± 1·79 years, respectively. The eye index ( I _E) of the silver shortfin eels was < 5·2 (mean 7·64 ± 0·29) and differed significantly from that of the yellow shortfin eels collected from two other sites. The I _E increased with L _T (mm) and was related by log I _E= 2·656 log L _T6·925. The per cent moisture, protein and ash content of the liver of silver shortfin eels was significantly lower than in yellow shortfin eels, but lipid content was significantly higher in the former (35·5 ± 2·0%). The mean mass μg mg lipid ⁻) of saturates (230·4 ± 2·6 v . 181·7 ±2·6), monoenes (367·4 ± 6·3 v . 290·8 ± 8·9) and PUFA (177·3 ± 5·3 v . 159·7 ± 4·6) in muscle was significantly higher, and the great majority of individual fatty acids was found also in higher quantities in silver shortfin eels. In the liver, the PUFA found in the highest quantity was 22:6n-3, except in shortfin eels from Hopkins River estuary, and the amount of 18:2n-6 in the liver of silver shortfin eels was significantly higher than that in yellow shortfin eels but the reverse was true of 20:4n-6. In both muscle and liver tissues the saturate 16:0 and the monoene 18:ln-9 collectively accounted for >50% of all the fatty acids in the lipid.     

Reproductive cycle and sexual maturity of the anglerfish Lophiomus setigerus in the East China Sea with a note on specialized spermatogenesis

The reproductive cycle and sexual maturity of the anglerfish Lophiomus setigerus were examined. Spermatids were released from the germinal cysts into the lumina of the seminal lobules, and both spermatids and spermatozoa were present in the lumina of the seminal lobules and sperm ducts. Spermatogenesis and vitellogenesis occurred throughout most of the year. The testes of males were full of spermatozoa throughout the year, with spawning from May to November. Males and females reached sexual maturity at a mean total length and age of 178 mm, 3.3 years and 303 mm, 6.1 years, respectively. There were clear seasonal cycles in the gonadosomatic index (I_G) and hepatosomatic index ( I _H) in females. The mean I_G of females increased rapidly with ovarian development while the mean I _H decreased from the middle of vitellogenesis to final maturation. Mean values of I _G and I _H in males increased with testicular development.     

Study of the sexual maturity of female bluefin tuna: purification and partial characterization of vitellogenin and its use in an enzyme-linked immunosorbent assay

Plasma steroid levels of female bluefin tuna (BFT) Thunnus thynnus rose from c. 1·5 ng ml⁻¹ during the quiescent period (March) to c. 7 ng ml⁻¹ during the ripening period (May). Testosterone (T) increased further to c. 8 ng ml⁻¹ during the pre-spawning period (June) while 17β-oestradiol (E₂) began to decrease. In the post-spawning period (August) steroid levels decreased to < 1 ng ml⁻¹. Vitellogenin (Vtg) plasma levels seemed to follow changes in E₂, showing an increase from the quiescent period to the ripening period of c. 18 mg ml⁻¹, decreasing slightly before spawning, and then decreasing after spawning. The Vtg content in plasma showed a good correlation both with the plasma levels of E₂ and T and with the percentage of vitellogenic oocytes at different periods of the reproductive cycle. Thus the ELISA could be taken as validated. Immunohistochemical staining of ovaries with anti BFT-Vtg serum demonstrated a high cross-reactivity with yolk proteins allowing the identification of vitellogenic oocytes.     

Effects of constant short and long photoperiod regimes on the spawning performance and sex steroid levels of female and male sea bass

Under constant short photoperiod, the spawning time of 2-year-old sea bass Dicentrarchus labrax was advanced as compared to controls, whereas spawnings were delayed under constant long photoperiod. High plasma levels of 17β-oestradiol (E_2/) and testosterone (T) in females were coincident with the appearance of vitellogenic oocytes in the ovary, while high levels of 11-ketotestosterone (11-KT) and T in males were coincident with the presence of spermiating males. Although plasma levels of E₂ in females and 11-KT in males were low during the remainder of the cycle, levels of T were always >1 ng ml⁻¹ in both sexes, suggesting that T could play an important role during the initial stages of gonadal development. The profiles of E₂ and T in females and 11-KT and T in males exposed to constant short days were similar to those in the control group, but fish which were maintained under constant long photoperiods showed a bimodal pattern of these steroids. The results obtained from fish exposed to constant photoperiod regimes provide further evidence that an endogenous process could be operating to control the reproduction of sea bass.     

The contribution of newly established populations to the dynamics of range expansion in a one-dimensional fluvial-estuarine system: rainbow trout (Oncorhynchus mykiss) in Eastern Quebec

Aim Rainbow trout (Oncorhynchus mykiss, Walbaum 1792) is an exotic salmonid invading eastern Canada. First introduced for recreational fishing in Ontario, Quebec and the Maritime provinces, the species is now spreading in salmon rivers located in Eastern Quebec, where its stocking is strictly forbidden. Newly established populations have been found along the St Lawrence Estuary. To effectively mitigate the potential threat the invasion poses to native salmonids, we aimed to document the invasion’s origin and progress in the St Lawrence River and estuary. We first determined genetic origins among several potential wild and cultured source populations, found at the upstream and downstream extremities of the St Lawrence system. Thereafter, we studied the range expansion, predicting that the invasion process conforms to a one‐dimensional stepping‐stone dispersion model. Location Recently invaded salmon rivers that flow into the Estuary and Gulf of St Lawrence in Quebec, and watercourses supporting naturalized populations (Lake Ontario, Lake Memphremagog and Prince‐Edward‐Island rivers). Methods Rainbow trout from 10 potential source populations (wild and domestic strains) and 243 specimens captured in salmon rivers were genotyped at 10 microsatellite loci. Genetic origins of specimens and relationship between colonies were assessed using assignment analyses based on individuals and clusters. Results Invasion of rainbow trout in Eastern Quebec is directed downstream, driven by migrants from upstream naturalized populations, found in the Ganaraska River (Lake Ontario), and, to a lesser extent, in Lake Memphremagog. Populations from the Maritime provinces and domestic strains do not contribute to the colonisation process. A recently established population in Charlevoix (Eastern Quebec) supplies other downstream colonies. Main conclusions Rainbow trout is spreading from Lake Ontario downstream to Eastern Quebec using the St Lawrence River system as an invasion corridor. Range expansion in a downstream direction is driven by a more complex stepping‐stone dispersion model than predicted. Management options to protect native salmonids include reducing the effective size of the Charlevoix population, impeding reproduction in recently colonized rivers, halting the upstream migration of anadromous spawners, and curtailing stocking events inside the stocking area.     

Effects of capture and recovery on plasma levels of cortisol, lactate and gonadal steroids in a natural population of rainbow trout

Rainbow trout were captured by angling from a run of spawning fish on the Tongariro River in northern New Zealand, to examine the effects of catch and release angling on stress and reproductive parameters. Fish were blood sampled immediately after capture at playing times of <5 or 15 min, or after 1 or 24 h of recovery in stream enclosures. Plasma samples were assayed for cortisol (F), lactate, testosterone (T), 17β-oestradiol (E₂), and 17a,20β-dihydroxy-4-pregnen-3-one (17,20βP). Plasma F levels were similar to those of hatchery stocks of rainbow trout, at capture, and became significantly elevated 1 h after capture. Plasma F was still clevated in some fish 24 h after capture. Plasma lactate levels began to increase 15 min after capture, were further elevated 1 h after capture, and had returned to normal 24 h after capture. We proposed that metabolic recovery had occurred but that some animals were still experiencing some degree of stress, possibly in response to holding conditions in the river. Both plasma T and E₂ were depressed 24 h after capture, whereas there was no change in plasma 17,20βP. This is consistent with other findings showing that acute stress is associated with depression of plasma levels of T and E₂. There was no mortality as a result of capture or any of the handling protocols. We conclude that catch and release angling will result in negligible mortality, but may have an inhibitory effect on some reproductive processes.     

Modulation of plasma membrane H+-ATPase from oat roots by lysophosphatidylcholine, free fatty acids and phospholipase A2

Plasma membrane vesicles were purified from 8-day-old oat ( Avena sativa L. cv. Brighton) roots in an aqueous polymer two-phase system. The plasma membranes possessed high specific ATPase activity [ca 4 μmol P₁ (mg protein)⁻¹ min⁻¹ at 37°C]. Addition of lysophosphatidylcholine (lyso-PC) produced a 2–3 fold activation of the plasma membrane ATPase, an effect due both to exposure of latent ATP binding sites and to a true activation of the enzyme. Lipid activation increased the affinity for ATP and caused a shift of the pH optimum of the H⁺ -ATPase activity to 6.75 as compared to pH 6.45 for the negative H⁺-ATPase. Activation was dependent on the chain length of the acyl group of the lyso-PC, with maximal activition obtained by palmitoyl lyso-PC. Free fatty acids also activated the membrane-bound H⁺-ATPase. This activation was also dependent on chain length and to the degree of unsaturation, with linolenic and arachidonic acid as the most efficient fatty acids. Exogenously added PC was hydrolyzed to lyso-PC and free fatty acids by an enzyme in the plasma membrane preparation, presumably of the phospholipase A type. Both lyso-PC and free fatty acids are products of phospholipase A₂ (EC 3.1.1.4) action, and addition of phospholipase A₂ from animal sources increased the H⁺-ATPase activity within seconds. Interaction with lipids and fatty acids could thus be part of the regulatory system for H⁺-ATPase activity in vivo, and the endogenous phospholipase may be involved in the regulation of the H⁺-ATPase activity in the plasma membranne.     

The status and distribution of lake sturgeon, Acipenser fulvescens, in the Canadian provinces of Manitoba, Ontario and Quebec: a genetic perspective

Genetic analysis of mitochondrial DNA sequence variation indicates that most of a sample of 396 lake sturgeon, Acipenser fulvescens, from the northern part of their range belonged to either one of two haplotypes. The vast majority of fish from the Great Lakes/St. Lawrence and Mississippi drainages were of a single haplotype while those from the Hudson/James Bay were composed of both haplotypes. This haplotypic distribution suggests that fish from one refugium (possibly Missourian) recolonized the Hudson-James Bay drainage while those from a second (possibly Mississippian) recolonized the Laurentian Great Lakes and St. Lawrence River. Lake sturgeon still inhabit much of their native postglacial distribution in Manitoba, Ontario and Quebec. However, the stresses of commercial overexploitation and habitat alteration, usually through hydroelectric dam construction and operation, have either singly or in tandem brought about the reduction, if not extirpation, of some populations within the range. The largest zone of extirpation and population reduction has occurred in the Lake Winnipeg drainage area, which covers more than one-third of Manitoba. Other areas where populations have been reduced to remnant levels, if not extirpated, include the lower Laurentian Great Lakes of Lake Ontario and Lake Erie. In northern Ontario, lake sturgeon populations whose riverine habitats have been fragmented by two or more dams are substantially reduced from their former levels. In Quebec, more attention has been paid to limiting the exploitive stresses on lake sturgeon populations. Combination of the genetic and status data suggests that both northern and southern populations of lake sturgeon (possibly from two glacial refugia) have been impacted severely from anthropogenic influences.     

Phototrophic growth on n-fatty acids by species of the genus Rhodocyclus sensu Imhoff et al.

Abstract Type strains of Rhodocyclus purpureus, R. gelatinosus and R. tenuis along with three local isolates of R. gelatinosus were tested for growth in the light on n -fatty acids ranging in chain length from C₅ (valerate) to C₂₂ (docosanoate).
R. purpureus , the type species of the genus, was anomalous in its limited ability to grow on n -fatty acids; no fatty acids of chain length greater than C₉ (nonanoate) were utilized. R. gelatinosus and R. tenuis , on the other hand, utilized all fatty acids in the range C₅ to C₁₈ inclusive. R. gelatinosus showed some restricted ability to use C₂₀ (eicosanoate) and C₂₂ (docosanoate) fatty acids.     

In vitro steroid production by isolated ovarian follicles of the striped trumpeter

Ovarian follicles from striped trumpeter Latris lineata were incubated in L15 medium alone, or medium supplemented with gonadotropin (GtH) preparations (human chorionic GtH, carp maturational GtH or partially purified salmon GtH), testosterone (T) or 17-hydroxyprogesterone (17P). Levels of oestrone (E₁), 17 β -oestradiol (E₂), T, and 17,20 β -dihydroxy-4-pregnen-3-one (17,20 β P) in the medium after incubation were measured by radioimmunoassay. Basal production of E₂ was high from previtellogenic follicles, whereas little T was produced. Both T and E₂ production increased in response to treatment with GtH or steroid precursors. Vitellogenic follicles showed basal production of both T and E₂, and T but not E₂ levels generally increased in response to hormone treatment. Preparations containing follicles nearing final maturation showed low basal production of E₂ but high production of T. Treatment with steroids resulted in little change in E₂ but often very large increases in T production, whereas GtH stimulated lesser increases. 17,20 β P production was detectable from incubations of maturing follicles from two out of five fish, and in those two incubations, increased in response to treatment with 17P. E₁ was not detectable in any incubations. The results indicate that there is a shift in steroidogenesis from E₂ to T production during oocyte development, and provide further evidence that steroid biosynthesis in non-salmonids is principally regulated by substrate availability.     

Stress-induced changes in concentrations of plasma sex steroids in black bream

Cortisol levels of black bream Acanthopagrus butcheri at capture did not change with time of day, gonadal stage or season and were 1·9±0·2 and 2·8±0·4 ng ml⁻¹ for male and female fish, respectively. Confinement resulted in significantly elevated cortisol levels at all time periods; however, levels after 24 h of confinement were significantly lower than peak cortisol levels (15 min for males and 1 h for females). Confinement stress resulted in reduced levels of 17β-oestradiol (E2) and testosterone (T) within 1 h in sexually mature females. In mature males, suppression of T and 11-ketotestosterone (11KT) occurred after 30 min and 6 h of confinement, respectively. The relationship between confinement stress and levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β P) was more complex, with levels in males being elevated after 15 min and 24 h and suppressed after 6 h of confinement. In contrast, 17, 20β P levels in females were elevated after 1 h of confinement. In regressed females, plasma E₂ and T concentrations were low at capture and were not affected by confinement stress whereas plasma 17, 20β P was elevated within 1 h. This study indicates that stress exerts a rapid inhibitory effect on gonadal steroidogenesis.     

Burst and coast use, swimming performance and metabolism of Atlantic cod Gadus morhua in sub-lethal hypoxic conditions

Prolonged swimming capacity (critical swimming speed, U _crit, protocol) and metabolism were measured for 14 Atlantic cod Gadus morhua exposed to seven oxygen levels within the non-lethal range normally encountered in the Gulf of St Lawrence (35 to 100% saturation). Burst-and-coast swimming was triggered earlier (at lower speeds) in hypoxia, and burst-and-coast movements were more frequent in hypoxia than in normoxia at low speeds. Furthermore, the metabolic scope beyond the metabolic rate at which Atlantic cod resorted to burst-and-coast movements decreased gradually as ambient oxygen concentration dropped. Overall, fewer burst-and-coast movements were observed in hypoxia while the distance swum in burst-and-coast mode remained c . 1% of the total distance swam in all tests. Oxygen availability had no effect on the rate of increase in metabolic rate with increasing velocity <50 cm s⁻¹_, but limited swimming performances and metabolic rate at higher speeds. The prevailing low oxygen tensions on the bottom in the deep channels may impair the swimming capacity of Atlantic cod in the estuary and northern Gulf of St Lawrence.