Return migration of Atlantic Salmon in the River Tana: Phases of migratory behaviour

From a total of 174 multi-sea-winter Atlantic salmon radio tagged in the Tanafjord (northern Norway, 70°N) during 1992 and 1993, 48 Atlantic salmon were followed from entering the River Tana until spawning. Three phases were identified: (1) migratory, direct or stepwise migration to, or close to the position held at spawning; (2) search, movements both up and down river at or close to the position held at spawning; (3) holding, a period without movements prior to spawning. During the migratory phase, Atlantic salmon migrated directly to near the spawning area, or stopped between one and nine shorter periods during the upstream migration. Number of stops increased with increasing migratory distance in 1993, but no such correlation was found in 1992. The highest migratory speeds were recorded in the lower parts of the river. A distinct change in migratory pattern was found in 67% of the Atlantic salmon near or at the area held at spawning. Most common was a search phase of erratic movements with more than one down river movement. After the movement terminated, 96% of the Atlantic salmon had a period when no or little movement was recorded until spawning (on average 55 days in 1992 and 51 days in 1993). There was no preference for staying at, up or down river from the spawning area during this holding period. Early ascending Atlantic salmon migrated to spawning areas further from the mouth than the later arriving Atlantic salmon in 1993, but not in 1992. The proportion of time spent on the migratory phase increased, while the proportion of time spent on the holding phase decreased with increasing distance to the spawning area.     

Maturation, spawning and growth of rock soles off Kodiak Island in the Gulf of Alaska

Northern rock sole Lepidopsetta polyxystra females from the Kodiak Island area, Alaska, reached 50% maturity at 328 mm L _T and an average age of 7 years. In contrast, southern rock sole Lepidopsetta bilineata females reached 50% maturity at 347 mm L _T and an average age of 9 years. Spawning started in midwinter for northern rock sole and peaked during the spring, while spawning for southern rock sole occurred during the summer. The bottom depth for spawning northern rock sole ranged from 43 to 61 m and averaged 45 m; spawning depth for southern rock sole ranged from 35 to 120m and averaged 78m. Both species appeared to develop a single stock of oocytes and to ovulate them in a single spawning. Northern rock sole females grew faster overall ( K =0.24) than southern rock sole females ( K =0.12) but reached a smaller maximum length ( L _∞=430 mm) than southern rock sole ( L _∞=520mm). Males of both species grew more slowly than females after 5 years of age and reached a smaller maximum length.     

Nereis succinea nuptial behavior: Does size matter?

Summary

Although Darwin noted that size may affect sexual selection, the effect of size on reproduction is controversial. Mature Nereis succinea, a polychaete that mates in pheromone-mediated twilight nuptial swarms, varies greatly in size, ranging more than 10-fold in body weight from 30 mg to >300 mg. Swim speed of swarming male worms increases with worm size, with the fastest males swimming more than twice the speed of the slowest. The female-produced spawning pheromone, nereithione, stimulates both swimming speed and spawning in males at concentrations of 10^?6 M and above, and lower concentrations cause significant activation of swimming. Individual worms can be stimulated to release sperm up to 40 or more times in a single experimental session. Larger worms release cumulatively more sperm than smaller ones, resulting in significant loss of body mass from repetitive spawning activated by nereithione. Size may enhance mating success of male N. succinea due to encountering more females as a result of faster swimming speed and due to the higher sperm density and number of spawning responses of large animals.     

青海湖裸鲤自然产卵场的生境特征及无人机遥测判别——以泉吉河为例

自然产卵场是维持物种延续最关键的栖息地,青海湖裸鲤（Gymnocypris przewalskii）的自然繁殖栖息地状况和生境特征尚缺乏详细的定量研究。以青海湖入湖河流泉吉河为例,在平水期采用现场调查和无人机遥测的方法对青海湖裸鲤的自然产卵场分布及生境状况进行调查,确定其产卵场生境特征参数,建立基于无人机遥测识别产卵场的方法并进行复核验证。结果表明：泉吉河河道形态可分为弯曲型、分汊型和顺直型等三种典型河型,青海湖裸鲤自然产卵场主要分布在弯曲型和分汊型河道中,分汊型河道几乎100%都有产卵场分布,弯曲型河道有70%为产卵场;产卵场河道平均长度（135.13±61.13） m,平均宽度（30.01±17.51） m,平均曲折度1.09±0.07;平均面积（4586.6±4201.61） m²;产卵场常位于缓水浅滩处,平均水深（0.19±0.10） m （范围：0.03-0.44m）,平均流速（0.24±0.20） m/s （范围：0.01-0.81m/s）,河床质为含有沙粒的卵石（粒径：163-256mm）底质。河道形态、沙洲分布、水深特征等特征参数可作为无人机遥测识别产卵场的判断条件,并实现验证成功。研究结果可为开展整个流域的青海湖裸鲤自然产卵场现状评估及保护对策制定提供技术支撑。     

Infection of the gonads of Glaucosoma hebvaicum by the nematode Philometva lateolabracis: occurrence and host response

The prevalence of infection of the West Australian dhufish Glaucosoma hebraicum off the lower west coast of Australia by Philometra lateolabracis was greater among females than males, which contrasts with the situation with Pagrus auratus in waters off New Zealand. Live P. lateolabracis were represented solely by females and were found only in the gonads of fish of mature size ( L ₅₀ at first maturity = c . 300 mm) caught between December and April and thus during the spawning period of dhufish. Since the gonads were largest during that period, they, and particularly ovaries, would provide an abundant food source in the form of blood. The prevalence of the parasite (live + dead individuals) increased with host body size to reach a maximum of c . 80% in the 700–799 mm length class of females and c . 50% in the largest length class of males. During the spawning period of G hebraicum, P. lateolabracis developed from small, non-gravid females to large gravid females, representing an increase in mass of more than 200 times. The maximum length of P. lateolabracis (470 mm) in G hebraicum is the greatest yet recorded for this species. Gonadosomatic indices provided no evidence that infection by P. lateolabracis leads to a conspicuous atrophy of the ovaries, which contrasts with the situation with the gonads of some of the teleosts infected by Philometra species, and presumably reflects, in part, the small volume of the ovary occupied by P. lateolabracis (c . 3%) and the low intensity of infection (mean = 2.0, maximum = 7). Although the presence of live P. lateolabracis did not stimulate an obvious tissue response by the ovaries during the spawning period of G. hebraicum , both the dead and any live parasites that remain after spawning become encapsulated in fibrous tissue.     

Genetic monitoring of progeny derived from natural spawning of Acipenser ruthenus Linnaeus, 1758 and Acipenser stellatus Pallas, 1771 as well as their hybrids in the Lower Volga river during the period 2017 to 2019

The state of natural spawning of sturgeons in the Lower Volga River was investigated through genetic monitoring of juveniles (larvae, fingerlings, subadults) captured at seven traditionally used monitoring locations. Sampling was performed during the period 2017–2019. In total, 460 individuals were caught and genotyped using a set of six microsatellite loci (Afug41, Afug51, Afug135, An20, AoxD161, AoxD165) and mtDNA control region sequencing. The observed species-specific microsatellite alleles revealed the presence of juvenile sturgeons originating from natural spawning also included some hybrids between Acipenser stellatus and A. ruthenus. Thus, the majority of sterlet breeding takes place in natural spawning grounds but also sterlet hybridizes with a small number of stellate sturgeons. Juveniles of other sturgeon species were not identified, and it is concluded that natural spawning activities of Russian sturgeon, beluga and ship sturgeon were insignificant or even absent in the Lower Volga during the observation period.     

Gonadal maturation,fecundity, spawning,and timing of reproduction in the mud snail,Cerithidea cingulata,a pest in milkfish ponds in the Philippines

Summary

Gonadal maturation, spawning, fecundity and timing of reproduction of the snail Cerithidea cingulata in a brackish water pond in Molo, Iloilo, Philippines, are described. Snails 4–41 mm in shell length were sampled monthly from May 1997 to May 1998; 25% were <25 mm, 67% were 20–30 mm, and 8% were >30 mm. The sexes are separate and could first be distinguished at 15 mm. Males are aphallic, have narrower shells than females of the same length, and have bright yellow-orange testes overlying the digestive gland deep inside the shell. Females have more robust shells, an ovipositor at the right side of the foot, and yellow-green ovaries overlying the digestive gland. The sex ratio was one male to two females in the pond population studied. Gonadal maturation was monitored by means of gonadosomatic index (GSI, gonad weight as a percent of visceral weight); maturation stages were based on the gonad appearance (immature, developing, mature) and histology (immature, developing, mature, redeveloping). GSI increased with snail size, and reached 16% in a 33-mm female. The smallest mature males and females were 18–19 mm, and most snails >20 mm were mature, spawning, or redeveloping. Histological sections showed all stages of gametogenesis in mature male snails. The oocyte size-frequency distributions in mature females showed mostly mature oocytes and secondary oocytes, but also oogonia and primary oocytes. GSI and the frequency of snails at different maturation stages varied over the year. Both GSI and the frequency of mature snails were highest during the summer months, April to August. Nevertheless, mature snails occurred throughout the whole year, as did mating and egg-laying. Fecundity (= number of oocytes >70 pμ) increased with size in mature females 2041 mm; an average 25-mm female produced about 1,500 oocytes and larger females produced a maximum of about 2,500 oocytes. Eggs strings laid on the pond bottom were 45–75 mm long; an average 64-mm string contained 2,000 eggs 210+20 pm in diameter. The density of eggs strings was highest (80–120/m²) during March-September. Eggs hatched after 6–7 d into planktonic veligers, which in turn settle on the pond bottom 11–12 d later as juveniles. Juveniles 2–6-mm long were most abundant in the pond during August-October.     

Mass propagation techniques currently being used in the spawning and rearing of marine fish species

Propagation techniques for marine fish species, applicable to public aquariums, are reviewed based on work with ornamental tropicals and foodfish species. Adult conditioning, spawning procedures, incubation of eggs, larval rearing, larval food culture, and facilities are discussed with specific references to techniques used at Instant Ocean Hatcheries, Inc, for Anemonefish (Amphiprion spp) culture in synthetic seawater.     

Nesting,eggs and larvae of triggerfishes (Balistidae)

Synopsis Triggerfishes construct nests by excavating depressions in sand. Eggs are laid in an adhesive mass and anchored with rubble. A photograph of a newly-hatched embryo is included.     

Reproductive biology of Bagrus docmak in the Victoria Nile,Uganda

Aspects of the reproductive biology of Bagrus docmak in the Victoria Nile were investigated between November 2005 and October 2006. Macroscopic and histological analysis of the gonads confirmed it as an asynchronous batch spawner which spawns throughout the year with bimodal spawning peaks coinciding with rainfall seasons. The first spawning peak occurred from March to May, the second from September to November. The sex ratio did not significantly deviate from 1:1. Length at sexual maturity was 33.6 cm and 31.6 cm fork length (FL) for females and males, respectively. Batch fecundity ranged from 1 000 eggs in 34 cm FL fish to 43 000 eggs in 79 cm FL fish, and correlated linearly with FL (r = 0.72) and body weight (r = 0.79). Mean relative batch fecundity was 6 eggs g^?1 (SE 2). These results could guide research into the possibility of artificially inducing the fish to spawn, and its subsequent culture.