A new method to evaluate egg‐to‐fry survival in salmonids, trials with Atlantic salmon

A new method to estimate the survival of salmonids from egg fertilization to fry emergence is described. Fine mesh screen cylindrical capsules, 12 cm³ in volume, filled with batches of 10 eggs of Atlantic salmon Salmo salar were implanted in the substratum using small removable guiding tubes inserted with a metal spike. The method was compared with two other commonly used techniques, capping redds with fry‐traps and fine mesh screen incubation‐emergence boxes buried into the gravel. Egg‐to‐fry survival was recorded for the three methods run in parallel in artificial redds created on three sites of the Nivelle River watershed (south‐west of France), two in the stream and one in an experimental spawning channel. In the channel, survival to the eyed stage and to hatching in capsules and incubation‐emergence boxes was also compared. The implant of capsules proved easier and faster to use than other methods, the structure of the surrounding substratum was less disturbed and the capsules were less vulnerable to spates. This technique provided survival values largely free of the bias induced by other methods and intermediate between that of incubators and of traps.     

Egg-to-fry survival of the sea trout in some streams of Gotland

The quality of the surface water of Gotland (Sweden) streams was good, and did not limit sea trout egg-to-fry (ETF) survival. The oxygen concentration of the interstitial water was positively correlated to the permeability of the stream bed, and to the geometric mean diameter of the substratum. When the oxygen at 15 cm inside the stream bed was undiminished from surface values, the permeability of the stream bed was at least 6000 cm h^–1 and the geometric mean diameter of the substratum at least 15.0 mm. When the interstitial oxygen concentration increased, the interstitial ammonium concentration decreased, the NO₂ concentration remained stable and the NO₃ concentration increased. The ETF survival up to hatching was highly dependent upon the oxygen concentration of the interstitial water. For survival from hatching to emergence, the geometric mean diameter of the substratum was the most important factor. ETF survival >50% was observed where the interstitial oxygen concentration averaged at least 10mg I-¹, the substratum permeability at least 2000cm h-¹ and the substratum geometric mean diameter at least 15 mm. Other factors, such as overdigging and drying out of the spawning grounds could increase the ETF mortality.     

Estimating population densities of salmonids in deep water in streams

Densities of salmon, trout and grayling were assessed in Scottish streams by systematic counting by underwater observers, where the water was greater than 1 m deep, and by using electrofishing equipment in adjacent shallower areas. Tests of the efficiencies of the two methods are described. Applications have included the estimation of production of trout, grayling and young salmon at a site on the River Tay and predicting the salmon smolt run of the River Tilt, and these applications are briefly described. The most suitable period for visual counting was summer, as at water temperatures of less than 15° C fish were hiding among stones in the stream bed. Wet weather hampered both electrofishing and visual counting.     

Sex ratio, spawning season and size at maturity of red bandfish in the western Aegean Sea

The red bandfish Cepola rubescens is characterized by a normal gonochoristic sexual organization. The overall male: female ratio did not differ significantly ( x ²=4.57, P <0.05) from the theoretical 1: 1. However, the male: female ratio differed with season and length class and these differences are most probably related to sexual differences in growth rate, natural mortality rate and energetic cost of reproduction. Red bandfish spawns over an extended period, from late spring to mid autumn, with larger females spawning earlier than smaller ones. Males reach maturity at a larger total length, 299 mm, and age, 2.6 years, than females, 219 mm and 1.9 years respectively, a fact most probably indicating the existence of social structure in red bandfish. Finally, red bandfish matures at a comparatively smaller length and age than other fish species.     

Symposium review: International symposium on the implications of salmonid growth variation

In Aberdeen, Scotland, in July 2000, aninternational symposium was held to presentresearch concerning the consequences of growthvariation for the ecology, evolution, andmanagement of salmonid fish. Presentationscovered important topics including linksbetween growth and mortality, interactionsbetween growth and life history, tradeoffsbetween growth and other fitness aspects, andevolutionary implications of growth variation. In addition, the symposium served as a showcaseof new approaches and technologies in salmonidresearch. In this review, I provide anoverview of the presentations, and summarizesome of the major emergent themes of thesymposium.     

A reconnaissance survey of the source of interstitial fine sediment recovered from salmonid spawning gravels in England and Wales

The declining salmonid populations reported for many rivers in England and Wales have frequently been attributed to spawning gravel siltation and the need to address this problem through sediment control strategies has been widely recognised. The planning of such sediment control strategies is, however, severely hampered by the lack of reliable information on the source of the fine sediment deposited within spawning gravels. Given the need for information on the source of the fine sediment accumulating in salmonid spawning gravels, a reconnaissance survey, based on the source fingerprinting approach, has been undertaken to establish the source of fine interstitial sediment recovered from spawning gravels in 18 important salmonid rivers in England and Wales. The findings confirm the potential of the fingerprinting approach for establishing the provenance of interstitial fines. More specifically, the results provide useful information on the relative importance of surface and channel/subsurface sources as the source of the interstitial fines collected from the individual study rivers. Significant regional contrasts in the source of this sediment are reported. The findings have important implications for the design and implementation of effective sediment management strategies aimed at protecting salmonid spawning gravels, in terms of both the sources to be targeted and the associated need to adopt different approaches in different rivers.     

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

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

Does spatial variation in egg thiamine and fatty‐acid concentration of Lake Michigan lake trout Salvelinus namaycush lead to differential early mortality syndrome and yolk oedema mortality in offspring?

Individual variation in fatty-acid and thiamine concentrations were determined in lake trout Salvelinus namaycush eggs collected at two spawning grounds in Lake Michigan. A suite of predictor variables, including spawning location, egg fatty-acid and thiamine concentrations, were used to attempt to explain cause-and-effect in early life stage mortality among S. namaycush families. Lipid and fatty-acid composition of S. namaycush eggs differed between spawning locations. Salvelinus namaycush offspring from south-western Lake Michigan were affected by a high occurrence of yolk oedema, whereas a higher frequency of early mortality syndrome (EMS) was observed among offspring from the north-western part of the lake. Random-forest regressions revealed location as the most influential predictor of yolk oedema mortality, whereas thiamine level in eggs was the strongest predictor of EMS-related mortality. Several polyunsaturated fatty acids were also found to be predictors of both mortalities. There is evidence of spatial variability in egg fatty-acid concentration among S. namaycush in Lake Michigan that, together with diminished thiamine concentration, contribute to low survival of S. namaycush progeny.     

The spread of furunculosis in salmonids in Norwegian rivers

Furunculosis was first discovered in a fish farm in Norway in 1964, following the importation of rainbow trout from Denmark. The disease spread to several farms and to wild fish in the River Numedalslågen, occurring there until 1979. It was eradicated at several farms, the last being disinfected in 1969. In 1985, furunculosis was discovered in marine fish farms in Nord-Trøndelag, following importation of salmon smolts from Scotland. The disease reached Møre og Romsdal in 1988, by which time 32 fish farms were infected in the two counties. By the end of 1992, 550 farms were infected. The disease spread concurrently in natural watercourses, from 22 in 1989, to 74 by the end of 1992. Rapid spread of the disease was associated with several factors including escapes from fish farms, possibly via transport of fish between farms, and natural movement of wild fish in the sea. The disease was not associated with particular physical characteristics in these watercourses, but large aggregations of fish beneath waterfalls combined with high water temperature may trigger disease outbreaks. The ecological consequences of furunculosis are not known. However, some river populations of adult salmon, sea trout and brown trout have suffered. Furunculosis may result in serious negative consequences for populations if a significant number of the brood stock die before spawning.     

Territorial and non-territorial spawning behaviour in the bream

The spawning behaviour of bream Abramis brama was studied in 1993, in a harbour on the River Meuse, Belgium. Fish spawned from 22 to 27 April and from 11 to 14 May, when the water temperature rose to 14.5) C. The reproductive behaviour of the bream was studied within a 15 m long part of the harbour using a video camera. Territorial males with tubercles (33–43 cm total length; >5 years old) defended bank areas of diameter 80–150 cm which included spawning substratum, i.e. roots of alder and willow trees and aquatic plants. Water depth ranged from 25 to 50 cm. Non-territorial males without tubercles (24–33 cm; 3–4 years old), remained 2–4 m away from the bank. Aggressive behaviour between males was frequent and, occasionally, males with tubercles were unable to defend a territory. Mature females (25–43 cm; >3 years old), coming from the deeper water of the surrounding area, were followed by non-territorial males before spawning in territories near the bank.     

Induction of nest building and spawning in Hoplosternum littorale

Sexually mature neotropical armoured catfish, Hoplosternum littorale were induced to build nests and spawn by reducing the conductivity of the water. Simulation of rain and increasing water level without a reduction in conductivity had no effect.     

Coral spawning in the western Pacific Ocean is related to solar insolation: evidence of multiple spawning events in Palau

Coral reproductive schedules have long been related to concomitant increases in regional sea surface temperature (SST). Yet, corals also mass spawn in the tropics, where SSTs vary little throughout the year. Here we show that the rise toward and fall from solar insolation maxima, which is the electromagnetic energy incident on the surface of the earth, coincide with coral spawning events in tropical Palau. Two insolation maxima (a consequence of the vernal and autumnal equinoxes) in the tropics lead to multiple spawning events per year. SSTs are poor predictors of coral spawning in the tropics. Multiple spawning events increase the rate of genetic recombination, which in turn may facilitate the likelihood of speciation and explain, in part, the high coral diversity in the tropics. We also show that mass spawning coincides with near-maximum solar insolation (5.0–7.2 kWh/m²/day) events from 33°N to 30°S in the western Pacific Ocean, and should be considered as one of the primary variables driving coral reproductive cycles.     

Female and male contribution to egg size in salmonids

Egg size contributes to other life history traits of an individual. It is traditionally considered as a maternally determined characteristic to which the male does not have any direct contribution. However, a recent finding in insects suggests that males can affect egg size also directly. In fish, the male effect could take place only during egg swelling, as the final egg size is reached after that. We studied egg size in four freshwater salmonid species (the land-locked Atlantic salmon, the brown trout, the Arctic charr and the lake trout) right after fertilisation (initial egg size) and after the swelling phase (final egg size). The results showed that the final egg size is affected not only by the initial egg size but also by both the female and the male through the process of egg swelling. This study suggests that paternal contribution may form a previously largely ignored source of variation in early life history traits in salmonid fish.     

Changes in the expression of genetic characteristics across cohorts in skeletal deformations of farmed salmonids

Genetic analysis of disorder incidence in farmed animals is challenged by two factors. Disorders in different cohorts and environments could be caused by different factors, leading to changes in heritability and to less than unity genetic correlations across cohorts. Moreover, due to computational limitations, liability scale heritabilities at very low incidence may differ from those estimated at higher incidence. We tested whether these two dilemmas occur in skeletal deformations of farmed salmonids using multigeneration data from the Finnish rainbow trout breeding programme and previous salmonid studies. The results showed that heritability was close to zero in cohorts in which management practices maintained incidence at a low level. When there was a management failure and incidence was unusually high, heritability was elevated. This may be due to computational limitations at very low incidence and/or because deformations are induced by different factors in different cohorts. Most genetic correlations between deformations recorded in different generations were weakly to strongly positive. However, also negative correlations between generations were present, showing that high liability at one time can be genetically connected to low liability at another time. The results emphasise that genetic architecture of binary traits can be influenced by trait expression.     

金沙江中游圆口铜鱼早期资源现状

2010年6月至7月在金沙江中游攀枝花格里坪金沙滩(26°35°28.96″N,101°31°52.01″E)设置同定采样断面,开展了金沙江中游圆口铜鱼早期资源现状的调查.结果表明,金沙江中游有金安桥、朵美、皮拉海、灰拉古、观音岩5个圆口铜鱼产卵场,产卵总量为3078.2万粒.圆口铜鱼的产卵行为和产卵量受江水的温度、流量、涨落水持续时间等多个因素的影响.调查期间圆口铜鱼的产卵初始时间为6月7日,盛期在6月下旬至7月上旬.近几年来,圆口铜鱼的产卵规模呈现出逐年下降的趋势,产卵场的位置也有所改变.通过了解金沙江中游江段圆口铜鱼早期资源分布状况,为金沙江中游圆口铜鱼资源保护提供了基础资料.