Biological specific features of the Lower Amur grayling Thymallus tugarinae (Salmoniformes: Thymallidae): 1. Age composition

We consider age composition of samples of the Lower Amur grayling Thymallus tugarinae inhabiting water bodies of the lower and middle course of the Amur and several rivers of the northwestern part of Sakhalin Island and the southern coast of the Sea of Okhotsk. Age composition of the Lower Amur grayling from the studied samples is not similar because of several reasons. In rivers of the Amur basin, the species has a maximal age of 6+.     

New data about distribution of lower Amur grayling <Emphasis Type="Italic">Thymallus tugarinae</Emphasis> and Baikal-Lena grayling <Emphasis Type="Italic">Thymallus</Emphasis> sp. (Thymallidae) in the basins of the upper Amur River and Zeya River

New findings of lower Amur grayling (Lower Amur grayling) Thymallus tugarinae and Baikal-Lena grayling Th. sp. (Th. baicalolenensis) in the basins of the upper Amur River and Zeya River are reported for 2010?2014. Lower Amur grayling has been registered in the tributaries of Argun River and in the middle stream of Ingoda River. Baikal-Lena grayling has been found for the first time in the headstream of Ingoda River. New data about the distribution of this species in the basin of upper stream of Zeya River are reported; particularly, Baikal-Lena grayling has been found in Okonon Lake; this is the first finding of a representative of Thymallidae family in the alpine lakes of the watershed area of Amur River. In the basins of upper Amur River and Zeya River, the summer ranges of upper Amur grayling Th. grubii grubii and lower Amur grayling overlap to some extent; on the other hand, the ranges of Baikal-Lena grayling and lower Amur grayling are disjoint. During the summer period, upper Amur grayling and Baikal-Lena grayling together inhabit the basin of upper stream of Zeya River, but only Baikal-Lena grayling has been found in the headstream of Zeya River. In the basin of upper Amur River (the headstream of Ingoda River), the joint range of these species is still unknown; the sympatric zone is located in Dzhermoltai River (the basin of Onon River).     

New species of grayling <Emphasis Type="Italic">Thymallus tugarinae</Emphasis> sp. nova (Thymallidae) from the Amur River Basin

Data on a new species, low Amur grayling Thymallus tugarinae sp. nova, inhabiting tributaries of the lower and middle current of the Amur River, are presented. This species has been earlier equated with the Amur grayling T. grubii, described by Dybowski (1869) from the rivers Onon and Ingoda (the Upper Amur Basin). The new species differs from other representatives of the genus in the body coloration, the pattern on the upper fin, and certain morphological characters. On most of the Amur Basin, the grayling from the Lower Amur is sympatric with T. grubii and in its tributary Bureya River, also with the Bureya grayling T. burejensis. Individuals with intermediate traits are unknown, pointing to reproductive isolation. These data are supported by the results of molecular-genetic analysis (Froufe et al., 2003, 2005; Knizhin et al., 2004).     

A new subspecies of the amur grayling Thymallus grubii flavomaculatus ssp. nova (Thymallidae)

A new subspecies of the Amur grayling is described, the yellow-spotted grayling Thymallus grubii flavomaculatus ssp. n. populating the upper reaches of large tributaries of the Lower Amur basin and some rivers flowing to the Tatar Strait, the Sea of Okhotsk, and the Sea of Japan. From nominative subspecies T. g. grubii populating the basin in the upper reaches of the Amur and from other representatives of the genus Thymallus, this subspecies differs in the dorsal fin pattern whose principal trait is a yellow spot on the last two-five interray membranes, in the body coloration, and in some morphological characters. The yellow-spotted grayling in the upper reaches of tributaries sympatrically coexists with the Lower Amur grayling Thymallus sp. No specimens with intermediate characters are found. The sympatric forms spawn at different times, thus being isolated reproductively. Isolation of the yellow-spotted grayling as a subspecies of the Amur grayling T. grubii is confirmed by the results of molecular-genetic investigations.     

Age and growth of kaluga Acipenser dauricus from the estuary of the Amur and its lagoon

Age composition and the rate of growth of kaluga Acipenser dauricus from the estuary of the Amur and the Amur lagoon have been analyzed. Differences in the distribution of juvenile and mature individuals of kaluga in the river estuary and the lagoon were revealed. Males are dominant among mature individuals aged 18–26 years, and females are dominanat at an age 27–43 years. Females and males of the same age do not differ in length and body weight. A decrease in the rate of linear and gravimetric growth of mature individuals at the modern stage (2005–2008) compared to the period of 1965–1982 was revealed. Juvenile individuals of kaluga from the near-estuarine part of the Amur and its lagoon are inferior in the rate of growth to fish of the same age caught in the river channel, 500 km to the south.     

Biological features of Low Amur grayling Thymallus tugarinae (Salmoniformes: Thymallidae): 2. Growth

We present the results of analysis of the group growth of the Low Amur grayling Thymallus tugarinae from 18 rivers of the Low Amur basin, tributaries of the Bureya and Ussuri rivers. We made use of the published data on the fishes of Sakhalin Island. The dwarf and fast-growing forms are not revealed among the investigated groups of this species. The parameters of growth of the Low Amur grayling in the investigated rivers are different, which is determined by the different conditions of feeding migration connected with the geographical location of the streams, their hydrological features, density of populations, etc. The anthropogenic factor influence is essential. Growth rate of T. tugarinae is lower compared with the other Amur species of graylings.     

Some features of the biology of the mud shrimp Upogebia issaeffi (Balls, 1913) (Decapoda: Upogebiidae) from the subtidal zone of Vostok Bay,Sea of Japan

The study of the biology of the mud shrimp Upogebia issaeffi (Balss, 1913) from the subtidal zone of the Vostok Bay (Peter the Great Bay, Sea of Japan) revealed that this species occurs at depth of 1–6 m on mixed grounds of boulders, gravel, pebbles, shells of dead clams, and silty sand. The average population density of U. issaeffi in the local aggregation on a bottom transect of 300 m length ranged from 0.2 ± 0.4 to 8.0 ± 3.0 ind./m², the biomass varied from 0.5 ± 1.1 to 78.7 ± 28.3 g/m², or about 2.7% of the total biomass of macrozoobenthos and 51.2% of the biomass of decapod crustaceans, which is characteristic of the habitats of the mud shrimp. The maximum depth of burrowing of U. issaeffi was 65 cm. The aggregation consisted of animals with body lengths of 44–88 mm. The lifespan of U. issaeffi was 2–3 years. An equilibrium ratio of males and females (1: 1.06) was observed in the population. There were egg clutches on pleopods of 81.7% of the females. The body size of the smallest females with eggs was 67 mm. The larger the females were, the more of them were ovigerous individuals. About 4% of individuals of U. issaeffi were infected with the parasitic isopod Orthione griffenis.     

Some biological aspects and life history strategies of Nile tilapia Oreochromis niloticus (L.) in Lake Victoria, Kenya

The life history characteristics of introduced Nile tilapia (Oreochromis niloticus L.) in Lake Victoria, including, sex ratio, fecundity, reproduction, weight‐length relationship and body condition were studied and compared with those of other populations. Samples were collected by trawling and seining in the Kenyan sector of Lake Victoria between June 1998 and December 2000. Males predominated over females (sex ratio 1.42 : 1 : 00). O. niloticus spawned throughout the year but with a peak between December and June. Length at first maturity was (mean ± SD) 30.81 ± 0.09 for females and 34.5 ± 6 0.48 for males. There was little seasonal variation in relative condition, which ranged from 0.92 to 1.05 in males and 0.94 to 1.07 in females. Gonadosomatic index (GSI) was low during the postspawning period (July to October) and high during the protracted breeding period (December and June). Fecundity ranged from 905 to 7619 oocytes for fish of 28 to 51 cm total length (TL) respectively. The relationships between fecundity (F) and total length (L), weight (W) and ovary weight (OW) were: F = 8.159L^1.53, F = 96.269W^0.4504, F = 1806 + 39.4OW. The slope b of the weight‐length relationship was 3.08–3.32 for males and 3.07–3.22 for females. Growth was allometric in both cases and was significantly different from the expected value of 3. The life history strategy of O. niloticus is discussed in context of environmental changes occurring in the lake.     

On the diversity of fishes in mountain lakes of the Amur basin

Results of the study of 11 lakes situated in the mountainous part of the Amur River basin are reported. Six fish species, namely, blunt-snouted lenok Brachymystax tumensis, Baikal-Lena grayling Thymallus baicalolenensis, Siberian stone loach Barbatula toni, Lagowski’s minnow Rhynchocypris lagowskii, Czekanowski’s minnow Rh. czekanowskii, and Amur sculpin Cottus szanaga, were found in five lakes. Four species were found in one lake (Lake Pereval’noe, basin of the Amgun’ River), and two species were found in each of the remaining lakes. Lenok and Amur sculpin were the most common species. The fauna of Lake Okonon (basin of the river Zeya) was the most specific and did not have analogs among the lake faunas; Czekanowski’s minnow and Baikal black grayling were found in this lake. The lenok ecotype that formed in the mountain lakes differed from the river lenok in some regards. The potential pathways of formation and protection of mountain lake ichthyocenoses of the Amur basin are discussed.     

A study of some autoecological parameters of southern barbel (Barbus meridionalis R.) in the Rentina stream, Greece

In our effort to give some information which investigates autecological parameters for southern barbel, a study of age, growth and reproduction for this species was carried out in the Rentina stream, northeastern Greece. The length-weight relationship can be described by the equations W = 0.008 L^3.159 and W = 0.0583 L^2.428 for females and males, respectively (W = body weight in g, L = fork length in cm). The most rapid growth in length occured during the first year of life (7.3 cm) after which growth decreased and remained constant at approximately 3.4 cm per year. The average density and biomass were 0.25 fish. m^-2 and 9.35 g. m^-2, respectively. The southern barbel becomes sexualy mature at the second year of life for both sexes. The mean absolute fecundity was 9119 ± 322 eggs with mean diameter 1.2 ± 0.2 mm. Spawning of this species, in the study area, occurs in June at mean temperature 19°C.     

Batch fecundity and spawning frequency of invasive Hemiculter leucisculus (Basilewsky, 1855) in Erhai Lake,China

Hemiculter leucisculus are multiple spawners with indeterminate fecundity, although previous fecundity estimates have assumed a determinate spawning pattern. Batch fecundity and spawning frequency of H. leucisculus were studied in Erhai Lake, China, in which the fish, as an exotic species, has become a successful colonizer. Spawning frequency was 16.05 %, as determined from the percent of females with postovulatory follicles 12 to 36 h old during the peak reproductive period (from May 27 to August 8). The average interval between spawning was 6.2 days and there were more than 16 total spawning batches during the peak reproductive period. The average batch fecundity (mean ± SD) was 11,934?±?5,921 hydrated oocytes in 40 females (standard length or SL: 9.1–14.4 cm), while relative batch fecundity was 560?±?137 eggs g^?1 wet weight. The total potential annual fecundity was approximately 190,944 oocytes over the whole spawning season and was much higher than the estimated standing stock (31,585 oocytes) of yolked oocytes (36 females, SL: 9.5–16.2 cm) at the beginning of the spawning season in April 2010. This high annual fecundity is likely to have contributed to successful invasion of Erhai Lake by H. leucisculus.     

Studies on grayling, Thymallus thymallus L., in Llyn Tegid and the upper River Dee, North Wales.

Scale and length/weight data from 2071 Llyn Tegid grayling and 1803 River Dee grayling were used for age and growth determinations. The time of scale annulus formation varied from autumn in some years to spring in other years. Seasonal changes in length, weight and the condition factor were described. The main growth period was from spring to autumn with very little growth occurring during the winter. Annual growth in length was back-calculated from scale measurements, and von Bertalanffy's model was fitted to the resulting length for age data. Comparisons were made between the specific growth rates and ultimate lengths ( L_x ) of Llyn Tegid and River Dee grayling, and between the growth of male and female grayling. Males grew faster than females after the onset of sexual maturity. Calculated lengths were converted to weights using a combined length/weight relationship for Llyn Tegid and River Dec grayling. Changes were evident in this relationship throughout the life of the fish.     

Age and growth of Siberian sculpin (Cottus poecilopus) and young brown trout (Salmo trutta) in a subalpine Norwegian river

Age, growth and density of Siberian sculpin (Cottus poecilopus) and young brown trout (Salmo trutta) within two sections of River Atna; above Lake Atnsjøen [Section 1 at altitudes between 739 and 715 m] and below Lake Atnsjøen [Section 2 at altitudes between 430 and 370 m] was studied during a 6-year period (1986–91). The water temperature was considerably lower in Section 1 than in Section 2, as the number of days with a water temperature above 10?°C (T _{D ≥ 10?° C} ) from spring to August 1 ranged between 2–26 and 26–52 days, respectively. Juvenile brown trout (age 0+) attained a significantly smaller body size in Section 1 than in Section 2; mean length ±SD was 35 ± 8 mm (ranged 27–46) and 43 ± 7 mm (range 38–46), respectively. In Section 2, there was a highly positive correlation between the body length of 0+ brown trout and mean water temperature in June (p<0.005), and also to some extent in Section 1 (p=0.11). Individuals of age 1+ did not exhibit any such difference, while fish in age group 2+ were larger in Section 1 than in Section 2. By using the number of days with a water temperature between the range 5–10?°C (T _{D ≥ 5 ? 10?° C} ) as test variables, we found a highly positive correlation between the August 1 body length of 0+ brown trout and T _{D ≥ 9}?°C from spring to August 1 in Section 2 (p<0.05), as opposed to T _{D ≥ 7}?°C for trout in Section 1 (p=0.11). Young Siberian sculpin (age 0+ and 1+) also exhibited slower growth in Section 1 than in Section 2, but this was not the case among older specimens. In the year with the lowest temperature measured (1987), no 0+ Siberian sculpin were caught in any of the two sections, indicating that low temperature affects their survival. Both species exhibited large spatial and temporal variation in density. Thus, data on abundance and growth sampled on one occasion at one site can not be regarded as representative for these two fish populations.     

Spawning seasonality and body sizes at sexual maturity in the bluespine unicornfish,Naso unicornis (Acanthuridae)

We herein evaluate several reproductive metrics of Hawaiian Archipelagic populations of the bluespine unicornfish (Naso unicornis), an economically and ecologically important, broadly distributed tropical Pacific reef fish, based on multi-year, fishery-dependent and fishery-independent collections. Sex-specific spawning seasonality was characterized for fish collected mostly from Oahu (Main Hawaiian Islands, MHI) using a gonadosomatic index. Histological slides preparations were used to score gonad developmental phase and to classify individuals of either sex as immature or mature. Sex-specific median body lengths at maturity (L₅₀) were estimated by logistic fits of proportion mature versus length class. Spawning was highly seasonal in Hawaii, with a single brief (May–June) peak spawning period. Proportionate gonad-to-body weight values were relatively low, averaging only about 0.1 % and 0.6 % across all months of year and 0.16 % and 1.03 % during May–June for males and females, respectively. Median lengths at sexual maturity differed between the sexes. L₅₀ values for fish collected throughout all months of year were 30.1 ± 0.5 (standard error) cm Fork Length (FL) for males and 35.5 ± 0.7 cm FL for females. Spawning seasonality and L₅₀ estimates for bluespine unicornfish in Hawaii suggest that the species spawns several months earlier in the calendar year and matures at larger body lengths in Hawaii versus Guam, the Northern Mariana Islands, and Pohnpei in the Federated States of Micronesia. Estimated lengths at sexual maturity are compared to the minimum length (14 inches or 35.6 cm FL) mandated for this species in Hawaii: median size at maturity occurs at a length appreciably less than (males) or approximately equal to (females) minimum legal size. A likely disproportionately large contribution of old females to population replenishment is discussed relative to the minimum size limit.     

Effect of dietary chitosan on challenged <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> post larvae with <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

Effect of different dietary squilla chitosan (Csq) concentrations: 0 (control), 0.5, 1 and 2 g 100 g^–1 diets were studied for weaned sea bass (Dicentrarchus labrax) post larvae. Post larvae were challenged with Aeromonas hydrophila after 5 feeding days, in order to monitor the prophylactic effect on the Csq fed larvae. The experiment started with an average initial weight of 50 ± 2 mg and total length of 12 ± 2 mm for post larval stage (40 days post hatch; dph), then continued feeding diets for a period of 20 days. Larvae survival percentage (%), mean total length (TL), width (W), total weight (TW), total weight gain (TWG), average daily weight (ADW) and specific growth rate (SGR) were recorded as morphometric measurements representing growth compared to the control groups. The results revealed that 1g Csq 100 g^–1 diet at P < 0.05 was the most effective concentration that achieved higher survival percentages; 94.5 ± 0.5 and 74 ± 2.0%, increasing the specific growth rate by 7.22% and 5.77% for non challenged and challenged weaned larval groups, respectively. Otherwise, the control challenged group displayed the lowest performance in all assayed parameters with the coincidental decrease in the survival % and specific growth rates. Similarly, lower growth performance was also observed at 2 g 100 g^–1 diet. Thus, the incorporation of chitosan at a level of 1g in fish diet enhanced the performance and reduced the fish mortality under stress conditions.     

Morphological and molecular analysis of Henneguya lagunensis n. sp. (Cnidaria,Myxosporea) parasitizing the gills of Eugerres brasilianus from Brazil

Plasmodia containing myxospores belonging to the genus Henneguya Thélohan, 1892 were found in the gills of Eugerres brasilianus (Cuvier, 1830). Despite the economic importance, few parasitological studies have been done with this species. We describe Henneguya lagunensis n. sp. using morphological and molecular data. The mature myxospores were rounded, measuring 29.1 ± 2.2 μm in total length, 8.2 ± 1.0 μm in body length, 7.9 ± 0.2 μm in body width, 20.7 ± 2.4 μm in tail length and 4.8 ± 1.0 μm in thickness. The polar capsules measured 3.3 ± 0.4 in length and 1.7 ± 0.3 μm in width. Polar filaments had 4–5 turns, helical. Phylogenetic analysis showed Henneguya lagunensis n. sp. as a sister species of Henneguya cynoscioni Dyková, Buron, Roumillat and Fiala, 2011, within a clade that contained mostly Henneguya species that parasitize marine fish of the order Perciformes. This is the first report of a species of Henneguya parasitizing Eugerres brasilianus.     

Determination of batch fecundity in Uranoscopus scaber Linnaeus, 1758 from the Aegean Sea, Turkey

This work focuses on reproductive biology aspects of Uranoscopus scaber from the coast of the Aegean Sea. In total, 175 U. scaber specimens were collected in Izmir Bay using trawl nets from January to December 2005. The reproduction period according to gonadosomatic index (GSI) values extents from March to September, with a peak in May (6.32 ± 1.2). Oocyte diameters taken from 59 mature gonads ranged from 62 to 1860 μm. Maximum batch fecundity (BF) was 58091 (mean: 11556 ± 1445) in large oocytes in May, and 8408 (mean: 2821 ± 945) in hydrated oocytes in September. The BF increased with total length and body weight, excluding the ovaries. Total length (TL)–BF relationships and fish weight–BF relationships were BF = 0.0034TL^4.6248 (r = 0.47) and BF = 59.166W?3101 (r = 0.49), respectively, according to the oocyte size frequency method. There was a linear relationship between BF and fish size.     

Basic characteristics of the population dynamic and state of exploitation of Moroccan white seabream Diplodus sargus cadenati (Sparidae) in the Canarian archipelago

Moroccan white seabream Diplodus sargus cadenati (n = 603) were caught off the Canary Islands from April 2000 to March 2001. Total length ranged from 46 to 404 mm. The subspecies was characterized as being dygynous with partial protandry. Overall ratio of males to females was 1 : 2.9. The reproductive season extended from December to May, with a peak in spawning activity in January–February. Fifty per cent maturity was reached at 201 mm total length in males and 216 mm in females. The length–weight relationship for all individuals was described by the following parameters: a = 0.000023, and b = 2.96, when length is given in millimeters and weight in grams. Fish of 0–12 years in age were found. The von Bertalanffy growth parameters for the entire population were: L_∞ = 467 mm, k = 0.143 year^?1 and t₀ = ?2.14 year. Growth parameters differed between males and females. For all fish, instantaneous rates of mortality were Z = 0.68 year^?1, M = 0.31 ± 0.6 year^?1 and F = 0.37 ± 0.6 year^?1; the exploitation ratio was E = 0.54 ± 0.9. Length at first capture for all individuals was 173 mm. The stock exploited above is an assumed optimum.     

Reduced growth and reproductive investment of Hemiculter leucisculus (Cyprinidae) in a reservoir with introduced icefish Neosalanx taihuensis (Salangidae)

Neosalanx taihuensis is an important zooplanktivorous commercial fish that has been widely introduced into Chinese freshwaters. Introduction of this species has induced decline and even extinction of native fish species in some waters. In this study, impacts of N. taihuensis introduction on growth and reproductive characteristics of an indigenous zooplanktivorous fish Hemiculter leucisculus were investigated by comparing population traits of the latter species in two reservoirs that differ only in whether N. taihuensis has been introduced. Huangshi Reservoir (HSR) and Mengquan Reservoir (MQR) are geographically proximate and display similar nutrient regimes and native fish faunas, but N. taihuensis has been stocked only in HSR. Populations of H. leucisculus in both reservoirs consisted of three age groups, ranging from age 1 to 3. Standard length (SL), body weight and back-calculated SL-at-age of H. leucisculus in HSR were significantly less than in MQR for both males and females in each age group. Female H. leucisculus also tended to produce fewer and smaller eggs (indicated by lower absolute fecundity, gonad weight and smaller egg diameter) in HSR than in MQR for each age group. We suggest that reduced growth and reproductive investment by H. leucisculus in HSR are likely the result of N. taihuensis introduction.