Feeding,somatic condition and survival of sand lance <Emphasis Type="Italic">Ammodytes</Emphasis> sp. larvae in Mutsu Bay,Japan

To clarify the recruitment process of sand lance Ammodytes sp., we investigated larval condition factor, relative gut fullness (%GF), prey abundance and oceanographic structure in Mutsu Bay, Japan, during 1999–2001. Ammodytes sp. larvae, which were collected by horizontal hauls of Motoda nets and a ring net at depths of 1, 10, 20, 30 and 40 m, were mainly distributed at 10–30 m. Larvae at the first feeding time until 12 mm in body length (BL) fed predominantly on copepod nauplii, whereas large larvae with BL of 12.1–14.0 mm fed on a mixture of copepod nauplii, copepodites and appendicularians from late February to April. A path analysis showed that difference in water density between 35- and 5-m depths negatively affected naupliar abundance at 10–30-m depth (standardised path coefficient β = ?0.71, p = 0.005 for 3.3–8.0-mm BL larvae and β = ?0.78, p < 0.001 for 8.1–12.0-mm BL larvae). Naupliar abundance positively affected the %GF of Ammodytes sp. larvae (β = 0.75, p < 0.001 for 3.3–8.0-mm BL larvae and β = 0.66, p < 0.001 for 8.1–12.0-mm BL larvae), whereas it was negatively affected by water temperature (β = ?0.45, p = 0.008 for 3.3–8.0-mm BL larvae and β = ?0.56, p = 0.002 for 8.1–12.0-mm BL larvae), and the temperature effect was weak compared with that of naupliar abundance. In turn, %GF positively affected larval somatic weight (β = 0.91, p < 0.001 for 6.0-mm BL larvae and β = 0.70, p = 0.005 for 10.0-mm BL larvae). The recruitment failure in 1999 was likely caused by a reduced condition factor, which resulted from low naupliar abundance. In contrast, the abundance of nauplii and Oithona similis copepodites was high in 2000 and 2001. It is possible that the higher recruitment success in 2001 was because of the higher water temperatures in Mutsu Bay, sustaining faster growth of the larvae than in 2000 under the high-prey abundance conditions.     

The efficacy of <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> vaccine preparations,administered to tilapia broodstock,in preventing streptococcosis in their offspring,via transfer of maternal immunity

This study aims to evaluate the efficacy of Streptococcus agalactiae vaccine preparations, administered to tilapia broodstock, in preventing streptococcosis, through specific and non-specific immunity being transferred to the offspring. The study was conducted in two phases. The first was the vaccination of the broodstock using a whole-cell vaccine, an extracellular product (ECP) vaccine, and a combination of the two with a ratio of 1:1. The vaccines were administered to the broodstock 2 and 3 weeks before spawning. The second phase was the challenge test for larvae produced by vaccinated broodstock, and larvae from the unvaccinated control broodstock, through immersion in a suspension of 10⁷ cfu mL^?1 pathogenic S. agalactiae for 30 min, at ages 7, 14, 21, and 28 days post-hatching. The parameters evaluated were the broodstock’s blood profile, antibody-lysozyme (in broodstock, eggs, and larvae), and the larvae’s relative percent survival. Treatment with the combined vaccine administered 3 weeks before spawning resulted in the broodstock having significantly better antibody levels, lysozyme activity, and hematology profiles, compared to the other treatments (p?<?0.05). In addition, the larvae produced by broodstock subjected to this treatment, when challenged with the pathogenic S. agalactiae at ages 7, 14, 21, and 28 days, had RPS values of 95.24, 83.33, 72.22, and 56.02%, respectively. It was concluded that the administration of the “whole-cell/ECP” combination vaccine preparation to tilapia broodstock in the 3 weeks before spawning can increase specific and non-specific immunity in the broodstock and protect the larvae from S. agalactiae infection.     

Development of osmoregulatory tissues in the Lake van fish (<Emphasis Type="Italic">Alburnus tarichi</Emphasis>) during larval development

Lake Van is one of the largest alkaline lakes worldwide and Lake Van Fish (Alburnus tarichi Güldenstädt, 1814) is the only vertebrate species inhabiting it. Lake Van Fish is an anadromous species that migrates to the streams (salinity 0.02%, pH 8.42) flowing into Lake Van (salinity 0.22%, pH 9.8) during the spawning period (April–July). Following spawning, fish return to Lake Van while larvae remain in fresh water. This study examined the development of osmoregulatory organs and the distribution of ionocytes in Lake Van Fish larvae adapting to the highly alkaline water characterizing the lake. Ionocytes were marked immunohistochemically and observed in whole mounts with immunofluorescence staining using the Na⁺/K⁺ ATPase antibody. Ionocytes were first identified in the yolk sac membrane and skin, and then in the gills, digestive tract, and kidneys of larvae. The number of ionocytes on yolk sac membrane and skin decreased during larval development, indicating ionocytes on these tissues have a role in larvae osmoregulation. Larvae hatched from eggs in stream waters die when transferred to Lake Van water but survived in lake water diluted with deionized water. Thus, larvae need to go through certain alterations at the cellular and organ levels in order to adapt to the conditions of Lake Van water, indicating they do not enter this lake immediately after hatching.     

Distribution of the early life stages of small yellow croaker in the Yangtze River estuary and adjacent waters

The horizontal distribution of the early life stages of small yellow croaker Larimichthys polyactis in the Yangtze River estuary and its adjacent area was investigated through six ichthyoplankton surveys conducted during the period of mid-April to mid-July 2015. A total of seven eggs and 2461 larvae and juveniles of small yellow croaker were collected. Abundance of the specimens was highest in mid-May and lowest in mid-July. The composition of the different development stages of small yellow croaker varied among the six cruises, although post-flexion larvae and juveniles dominated the ichthyoplankton collection in each cruise. Specimens at different development stages showed different distribution patterns in the study area. The eggs, yolk-sac and pre-flexion larvae were mainly collected at stations with depth exceeding 30 m, while post-flexion larvae and juveniles were mainly distributed in the relatively shallow waters near to the mouth of the Yangtze River. In conclusion, the study suggested that the study area had largely lost the ecological function to support small yellow croaker spawning, although it could still serve as nursery ground for the species.     

The effect of live feeds bathed with the red seaweed <Emphasis Type="Italic">Asparagopsis armata</Emphasis> on the survival,growth and physiology status of <Emphasis Type="Italic">Sparus aurata</Emphasis> larvae

Larval rearing is affected by a wide range of microorganisms that thrive in larviculture systems. Some seaweed species have metabolites capable of reducing the bacterial load. However, no studies have yet tested whether including seaweed metabolites on larval rearing systems has any effects on the larvae development. This work assessed the development of Sparus aurata larvae fed preys treated with an Asparagopsis armata product. Live prey, Brachionus spp. and Artemia sp., were immersed in a solution containing 0.5% of a commercial extract of A. armata (Ysaline 100, YSA) for 30 min, before being fed to seabream larvae (n = 4 each). In the control, the live feed was immersed in clear water. Larval parameters such as growth, survival, digestive capacity (structural-histology and functional-enzymatic activity), stress level (cortisol content), non-specific immune response (lysozyme activity), anti-bacterial activity (disc-diffusion assay) and microbiota quantification (fish larvae gut and rearing water) were monitored. Fish larvae digestive capacity, stress level and non-specific immune response were not affected by the use of YSA. The number of Vibrionaceae was significantly reduced both in water and larval gut when using YSA. Growth was enhanced for YSA treatment, but higher mortality was also observed, especially until 10 days after hatching (DAH). The mortality peak observed at 8 DAH for both treatments, but higher for YSA, indicates larval higher susceptibility at this development stage, suggesting that lower concentrations of YSA should be used until 10 DAH. The application of YSA after 10 DAH onwards promotes a safer rearing environment.     

Nursery habitat use for larval and juvenile Pacific herring Clupea pallasii in Miyako Bay on the Pacific coast of northern Japan

Fisheries Science - To clarify nursery habitat use for larval and juvenile Pacific herring Clupea pallasii, we collected eggs, larvae, and juveniles at several sampling sites in inner Miyako Bay...     

Hatchery broodstock conditioning of the blue mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> (Linnaeus, 1758). Part II. New formulated feeds offer new perspectives to commercial hatcheries

Five diets were compared for their efficiency at maturing the gonads of the blue mussel, Mytilus edulis. The diets consisted of a 1:1:1 mixture of Isochrysis galbana (T-Iso), Pavlova lutheri, and Chaetoceros calcitrans given at concentrations of 2.4 × 10¹¹ cells day^?1 for the positive control treatment (PF) and 3.0 × 10¹⁰ cells day^?1 (=1/8) for the negative control treatment (NF). The other three treatments, MB10+, MyStock+, and Frippak+, consisted of the NF diet supplemented with one of the micro-encapsulated diets MB10 (mixture of dried algae), MyStock (formulated diet), and FRiPPAK^® Fresh #1 CAR (larval shrimp diet) at a level of 0.2% of the live weight (LW). Treatments PF, MB10+, and MyStock+ led to high percentages of spawning animals (80, 78, and 85%, respectively) and large numbers of eggs (on average 3.0 × 10⁶ eggs female^?1). Females given the NF and Frippak+ treatments produced only half the number of eggs per female, and only 17 and 6%, respectively, of the animals spawned. A high hatching rate was observed for all treatments, 71% for the pure algae diets PF and NF and more than 80% for the micro-encapsulated diets. The larvae resulting from the NF treatment were smaller, with 41% of D-larvae measuring less than 90 μm, whereas with the other treatments only 5–11% belonged to that size category. The four most important fatty acids found in mussel eggs were 16:0, 16:1(n?7), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA); these represented at least 50% of the fatty acids in all treatments. The high DHA content of MB10 and MyStock was not reflected in the fatty acid composition of the eggs whereas the high concentration of linoleic acid in MyStock was. To our knowledge, this is the first time that mussels are successfully conditioned with formulated feeds.     

Winter longitudinal variation in the body size of larval fishes in the Seto Inland Sea,Japan

This study revealed the spatial variation in abundance and body size of larval fishes in the Seto Inland Sea, Japan, in January 2014 and 2015. Fish larvae were collected by a 1.3-m-diameter ring net towed at the surface and at 10-m depth at 21 stations. The most dominant species was the sandlance Ammodytes japonicus, constituting 82% of total larval fish caught. The body size of A. japonicus was greater [ca. 9 mm total length (TL) in 2014] in eastern areas than in western areas (ca. 5 mm TL in 2014). This trend was also observed in rockfishes (Sebastiscus marmoratus and Sebastes inermis species complex), suggesting a common phenomenon in this region. Because the water temperature was lower in eastern areas, it is likely that the longitudinal differences in larval body size are attributable to earlier spawning in eastern areas caused by different temperature conditions.     

Morphological and habitat characteristics of settling and newly settled Roughscale Sole Clidoderma asperrimum collected in the coastal waters of northeastern Japan

This report first describes the morphological and habitat characteristics of larval and juvenile Roughscale Sole Clidoderma asperrimum. Five metamorphosing larvae (22.1–31.7 mm standard length, SL) and 12 juveniles (23.7–46.4 mm SL) were collected from two locations in coastal waters of northeastern Japan, Shizugawa Bay (rocky habitats, 6–12 m depth) and Iwaki (sandy habitats, 10–50 m depth), respectively, using a hand net while SCUBA diving and a small trawl net during May–August in 2008 and 2010. Underwater observation in Shizugawa Bay revealed that metamorphosing larvae and juveniles that had settled on rocks or stones showed transparent and variegated body coloration, which is cryptic to a rocky habitat. Juveniles in Iwaki showed monotonic coloration. The settlement would occur during metamorphosis because the same larva observed on a stone subsequently swam with a left-lateralized body posture. The larval morphology was characterized by a dense covering of fine spines on the whole body surface. Spines on the ocular side developed steadily, gradually forming bony tubercles with growth, whereas those on the blind side regressed with development and finally disappeared in metamorphosed juveniles. Our results indicate that Roughscale Sole can settle and adapt to rocky and sandy habitats in coastal waters with wide depth range.     

Association between the planktonic larval and benthic stages of Manila clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> in eastern Hokkaido,Japan

The association between planktonic larval and benthic stages of Manila clam Ruditapes philippinarum and factors determining successful recruitment were studied in Akkeshi-ko estuary and Akkeshi Bay, Hokkaido, northern Japan. The field study showed that planktonic larvae were localized mainly in the bay after dispersal from the estuary and recruitment to the estuarine fishing grounds was not always successful. A numerical analysis suggested that estuarine circulation transported tracers, used to simulate planktonic larva, from the estuary to the bay but the number of returning tracers varied depending on the river discharge and wind direction. The planktonic larvae were affected by unsuitable conditions for survival in the estuary, such as high turbidity. We conclude that most larvae develop within the bay, where conditions are more saline and less turbid, and that although return to the estuary is essential for recruitment, it is not necessarily related to the abundance of larvae.     

Ontogenetic habitat shift in <Emphasis Type="Italic">Pugettia quadridens</Emphasis> on the coast of Sagami Bay,Japan

Population dynamics of the kelp crab Pugettia quadridens, a potential predator of juvenile abalone, were investigated on the coast of Nagai, Sagami Bay, to examine its cryptic ontogenetic habitat shift. Monthly quantitative sampling over 2 years, which was carried out in 11 different subtidal habitats (< 0.1–8 m deep), revealed that P. quadridens changes ontogenetically according to its habitat: P. quadridens occurred in shallow lower subtidal (1–4 m) small red algal turfs (mainly Grateoloupia cornea) almost all year around, when the population was dominated by juveniles and stage I (immature) individuals; on the other hand, in the shallow upper subtidal (0.1–1 m) habitat (mainly Sargassum fusiforme beds near the low tidal mark), P. quadridens occurred only during winter to early spring, when the population was dominated by individuals of senior ontogenetic stages. These finding suggest that P. quadridens inhabit subtidal small red algal turfs during their early benthic phase, and then, the majority of larger individuals of stages II and III migrate to Sargassum beds. Our results suggest that the impact of P. quadridens predation on abalone stocks is limited in the present study site, primarily because the habitat of P. quadridens is segregated from that of juvenile abalone.     

Oocyte maturation and active motility of spermatozoa are triggered by retinoic acid in pen shell <Emphasis Type="Italic">Atrina pectinata</Emphasis>

For recovery of the declining population of pen shells in the wild, the production of pen shell juveniles for transplantation or aquaculture is underway in Japan. For more stable juvenile production, artificial fertilization methods for pen shells are needed, but methods to induce oocyte maturation (meiosis resumption) used in other bivalves, which make oocytes fertilizable, were ineffective for pen shells. Here, we report evidence showing that retinoic acid (RA) has strong activity in inducing oocyte maturation and activating sperm motility in pen shells. Treatment of fully developed oocytes with 1.0 μM all-trans-RA (at-RA) induced germinal vesicle breakdown, a typical morphological sign of oocyte maturation, but 1.0 μM at-retinol and at-retinal, 2 mM ammonia, and 1.0 μM serotonin were ineffective. Treatment with at-RA for 30 min was sufficient for oocyte maturation and was more potent than its isomers, 9-cis- and 13-cis-RA. Parallel results were obtained for sperm motility activation. Oocyte responsiveness to at-RA increased during the final stage of ovary development. Artificial fertilization was successful only with the oocytes treated with at-RA, and fertilized eggs developed to D-shaped (veliger) larvae without apparent morphological abnormalities. These results indicate the possible application of RA for the artificial fertilization of pen shells.     

Occurrence and density of Pacific saury Cololabis saira larvae and juveniles in relation to environmental factors during the winter spawning season in the Kuroshio Current system

The occurrence and density of Pacific saury Cololabis saira larvae and juveniles were examined in relation to environmental factors during the winter spawning season in the Kuroshio Current system, based on samples from extensive surveys off the Pacific coast of Japan in 2003–2012. Dense distributions of larvae and juveniles were observed in areas around and on the offshore side of the Kuroshio axis except during a large Kuroshio meander year (2005). The relationships of larval and juvenile occurrence and density given the occurrence to sea surface temperature (SST), salinity (SSS), and chlorophyll‐a concentration (CHL) were examined by generalized additive models for 10‐mm size classes up to 40 mm. In general, the optimal SST for larval and juvenile occurrence and density given the occurrence was consistently observed at 19–20°C. The patterns were more complex for SSS, but a peak in occurrence was observed at 34.75–34.80. In contrast, there were negative relationships of occurrence and density given the occurrence to CHL. These patterns tended to be consistent among different size classes, although the patterns differed for the smallest size class depending on environmental factors. Synthetically, the window for spawning and larval and juvenile occurrence and density seems to be largely determined by physical factors, in particular temperature. The environmental conditions which larvae and juveniles encounter would be maintained while they are transported. The survival success under the physically favorable but food‐poor conditions of the Kuroshio Current system could be key to their recruitment success.     

Ontogenetic habitat shift of age-0 Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> on the Pacific coast of northeastern Japan: differences in timing of the shift among areas and potential effects on recruitment success

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30–80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June–August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success.     

Effect of diets supplemented with feed additives on growth,feed utilization,survival, body composition and intestinal bacterial load of early weaning European seabass, <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> post-larvae

The present study was carried out to evaluate the effect of supplementation of Garlen®, Diamond V XPC®, and Bactozyme® and their combination in the diets of European sea bass, Dicentrarchus labrax larvae development in hatcheries on feed intake, growth performance, feed efficiency, intestinal bacterial, survival rate, and economics analysis. Dicentrarchus labrax juveniles (1.4 ± 0.5 mg) were distributed into eight experimental groups with a density of 2.5 larvae per liter. Eight iso-nitrogenous (55% crude protein) and iso-caloric (19.2 ± 0.2 MJ/kg, DM) weaning diets were formulated to contain the control diet (no feed additives), individually or mixed alternatively with three feed additives (Garlen®; Diamond V XPC®, and Bactozyme®). Each experimental diet was allocated to three tanks of fish and fed for 12 weeks. Growth and survival rate (S %) were improved for larvae fed the diets supplied with either (Diamond V XPC® + Bactozyme®) or (Garlen® + Diamond V XPC® + Bactozyme®), respectively compared to the control larvae group. The best FCR value was recorded for larvae fed a diet supply with (Garlen® + Diamond V XPC® + Bactozyme®), while the control larvae group recorded the worst FCR. The optimum significant (P ≤ 0.05) nutrient utilization values, larvae body crude protein content, activity test (ATV%), and profit index (PI) values were observed for larvae fed a diet containing Diamond V XPC® + Bactozyme® or Garlen® + Diamond V XPC + Bactozyme® compared to other treatments. The opposite trend was observed for total bacterial (TBC) and Vibrio sp. counts. No significant (P ≥ 0.01) difference was recorded in Aeromonas sp. count values in all experimental treatments. The results from this study show that (Garlen®; Diamond V XPC®, and Bactozyme®) individually or mixed alternately as growth promoters and immune stimulants in early weaning larval diets of European sea bass under hatchery conditions led to improve growth performance, feed utilization, survival, lowest intestinal bacterial load, and highest profit index (LE).     

Winter monsoon promotes the transport of Japanese temperate bass Lateolabrax japonicus eggs and larvae toward the innermost part of Tango Bay,the Sea of Japan

Northwesterly cold winds characteristic of the East Asian Winter Monsoon (EAWM) dictate winter climatic conditions over the Japanese Archipelago. Japanese temperate bass Lateolabrax japonicus is a commercially important coastal fish that spawns offshore in winter and uses shallow waters as nursery habitats. To investigate the effects of EAWM on the planktonic period of L. japonicus, eggs, larvae, and juveniles were quantitatively collected in Tango Bay on the Sea of Japan side in winter and spring from 2007 to 2017. Although eggs occurred close to the mouth of the bay, planktonic larvae occurred further inside as they developed. The horizontal distribution of planktonic larvae, combined with water velocity data obtained from mooring observations, indicated that planktonic larvae are transported south‐ to westward through Ekman current and an anticyclonic circulation, which are driven by northwesterly winds. To evaluate survival during the planktonic period in each year class, the abundance of benthic larvae/juveniles was divided by winter total landings of Lateolabrax spp. (proxy of the spawning stock size). This survival index exhibited a positive correlation with the northwesterly component of winter winds, and a negative correlation with winter air temperature (average from December to February, Spearman's correlation, p < .05). There was, however, no significant correlation with winter water temperature or winter freshwater discharge in the bay. We conclude that northwesterly cold winds of EAWM play a critical role in transporting L. japonicus eggs and larvae toward nursery habitats, specifically beaches and estuaries fringing the innermost part of Tango Bay.     

Development of phototaxis in the early life stages of Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

We investigated the development of phototaxis in larval and early juvenile stages of Pacific bluefin tuna Thunnus orientalis to detail behavior development in relation to light. We observed the distribution of Pacific bluefin tuna in an illumination gradient tank from 1 to 26 days after hatching (DAH). Two long rectangular tanks (100 × 10 × 10 cm) were used for experiments; each tank was divided into four sections for observations and one tank was equally illuminated at 1.0 × 10³ lx as the control tank, and the other was at 4.0 × 10², 1.0 × 10³, 1.0 × 10⁴ and 7.0 × 10⁴ lx as the illumination gradient tank. Laboratory-reared larvae and juvenile were released into each tank and acclimatized for 10 min. Thereafter, the number of individuals in each section was counted for 5 times with 10-min intervals. Until 2 DAH (3.6 ± 0.1 mm BL), larvae distributed homogeneously in each section in both tanks. After 3 DAH (3.7 ± 0.1 mm BL) when the eyes of the larvae were pigmented, most fish moved into the 7.0 × 10⁴ lx section in the illumination gradient tank, while fish in the control tank maintained a uniform distribution during the experimental period (Chi-square test, P < 0.05). The results suggest that the post-larvae and juvenile stages show strong positive phototaxis.     

Ontogenetic habitat and dietary shifts in Japanese turban snail <Emphasis Type="Italic">Turbo cornutus</Emphasis> at Nagai,Sagami Bay,Japan

A field survey and a laboratory experiment were conducted to examine ontogenetic shifts in habitat and diet of the turban snail Turbo cornutus. The main habitat of turban snail juveniles smaller than 10 mm shell height (SH) was turfs of articulated coralline algae, and that of adults larger than 50 mm SH was kelp beds of Ecklonia bicyclis and Ecklonia cava. However, the ontogenetic habitat shift during the juvenile stage of 20–50 mm SH was unclear. From the results of a long-term feeding experiment and stable isotope analysis, the gelidiacean alga Gelidium elegans was assumed to be more important as a food source for juvenile turban snail than E. cava in the field. However, the frequency of individuals inhabiting gelidiacean algal turfs was low in both juvenile and adult stages. Thus, the ontogenetic shifts in habitat and diet did not coincide and other factors, i.e., daytime refuge, are important. As the growth rate was higher in the juveniles fed on the two algal species than those fed on single algal species, co-occurrence of various algal habitats in rocky shore ecosystems as a coastal ecosystem complex may enhance growth of turban snail juveniles feeding on a combination of different algal species.     

Impact of food type on growth,survival and reproduction of the cyclopoid copepod <Emphasis Type="Italic">Cyclopina kasignete</Emphasis> as a potential live food in aquaculture

This study compared the efficacy of different dietary algae on the growth and reproduction of the cyclopoid copepod Cyclopina kasignete, a potential live food species for fish larvae in aquaculture. The experimental diets for the copepod consisted of three monoalgal diets (Nannochloropsis oculata, Tisochrysis lutea and dry Melosira sp.) and two mixed algae diets (T. lutea?+?N. oculata, T. lutea?+?dry Melosira sp.). The experiment was carried out for 30 days, and the population growth, survival and reproductive performance (generation time, hatching rate, life spawning times, daily offspring production, eggs per sac, lifespan and sex ratio) were used to assess the responses of C. kasignete to different food types. Population growth, survival and reproductive capacities of C. kasignete were significantly affected by the mono and binary species of algal diets. The results showed that copepods exhibited superior growth, survival and productivity when fed on fresh T. lutea, dry Melosira sp. and a mixture of both species compared to other dietary treatments. Copepods produced comparable growth, survival and productivity when fed on diatoms (dry Melosira sp.) as a single or in combination with other algae. This study indicates that cyclopoid copepod C. kasignete grow fast and have the potential to serve as a live food for aquaculture. The algae T. lutea, dry Melosira sp. and their combination are appropriate food to sustain the growth and reproduction of this copepods in mass culture as a potential live food in fish hatchery.     

Reproductive characteristics of <Emphasis Type="Italic">Gymnocypris firmispinatus</Emphasis> in the Anning River,China

The reproductive characteristics of Gymnocypris firmispinatus were determined from 582 individuals collected in the Anning River, China. The sex ratio (male: female) was 1:1 for the overall population but 3.1:1 for the mature group. Females reached a larger total length and total weight (242 mm and 148.17 g) than males (163 mm and 41.58 g). Lengths and ages at maturity were estimated to be 83.4 mm and 2.4 years for males, 130.7 mm and 5.9 years for females, respectively. Based on the analyses of gonad development and the size distribution of oocytes, G. firmispinatus spawned from March to May with high degree of the spawning synchronicity. The opposite tendency between gonado-somatic index and hepato-somatic index from January to March in females indicated that the energy requirement for the oocytes growth may be derived from the liver. In addition, the estimated mean fecundity and mean relative fecundity were 1227 and 29.7 eggs per g total weight. The fecundity of G. firmispinatus increased linearly with increasing of total length, total weight and ovary weight. This study provides details about the reproduction suggesting that G. firmispinatus might be especially vulnerable to exploitation in the Anning River.