Male reproductive strategy and reserve allocation in sand smelt from brackish lagoons of southern France

In male sand smelt Atherina boyeri , from three coastal brackish lagoons of southern France, the duration of the reproductive season differed according to fish size: larger fish exhibited an extended reproductive season from February to August while smaller males reproduced only from April to June-July. Smaller and larger fish showed differences in their seasonal pattern of reserves. Through the cold season, energy content was exhausted for over-winter maintenance and reproductive needs, and was restored just after fish ceased reproducing. In smaller fish, however, reserves were more rapidly restored than in larger fish, and exhibited a decrease in autumn. This result suggested that small fish invested their energy into growth and winter survival rather than reproduction while older fish invested in reproduction. These results are discussed in terms of life history Strategies.     

Resident spawning of Japanese smelt,Hypomesus nipponensis,along gravel shorelines in Lake Nojiri,Central Japan

In Lake Nojiri, the Japanese smelt, Hypomesus nipponensis McAllister, 1963, population has been thought to be maintained by artificial spawning, and stocking efforts as natural spawning in in-flowing streams is unlikely due to the lack of inflowing stream habitat. In this study, novel resident Japanese smelt spawning was observed along the lakeshore in shallow areas with clean gravel and flow. Spawning occurred at night during early March to mid-April and eggs, confirmed on gravel substrate, progressed to the eyed state in 5–6 weeks. Although natural spawning was observed, the ratio of eggs that progressed to the eyed stage was minimal, possibly due to thick algae cover in areas with low flow velocity. Therefore, resident Japanese smelt spawning along the lake shoreline is physically possible and potentially contributes to the overall population in Lake Nojiri, but in-lake spawning alone presumably is not a biologically viable method for population sustainability due to low survival rates and egg density at present. Environmental improvements such as construction of fish ladders to suitable in-flowing spawning habitat, introduction of clean gravel to shorelines, and water level management adjusted to the smelt spawning run would contribute to higher recruitment by natural smelt reproduction, and consequently enhance the smelt production in Lake Nojiri.

     

Analyses of growth processes of pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, through the use of daily otolith increments

It has been reported that pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, appear in small and large size groups during spawning despite being an annual fish. It is hypothesized that pond smelt have a bimodal life history, anadromous for large size groups and resident in the lake for small size groups. We calculated the body length and growth rate of the small and large size groups through the use of daily otolith increments and compared growth parameters between groups. In addition, the growth processes of resident fish in Lake Ogawara and anadromous fish in the adjacent sea were examined and compared with small and large size groups, respectively. We found that the two size groups diverged after 40–50 days from hatching with significant size groups present after 50 days. Through otolith increment analysis the growth processes of the small and large size groups were correlated with resident and anadromous forms respectively. These results revealed the utility of otolith increment analyses to clarify population structure of this species.     

European smelt Osmerus eperlanus in the eastern Gulf of Finland,Baltic Sea: Stock status and fishery

In the eastern Gulf of Finland, European smelt Osmerus eperlanus occurs as an anadromous ecological form that spawns in coastal, low-salinity zones and in several rivers entering the gulf, most importantly in the River Neva. Osmerus eperlanus is a key commercial fish species for the population of St. Petersburg, and the city's fish symbol. However, the state of the smelt stock has considerably deteriorated over the past few decades. Monitoring shows that annual catches during 1965–1992 averaged 2274 t, compared to 292 t in 2002–2017, although some improvement is inidicated by a gradual increase in catches in recent years (e.g., to 595 t in 2017). This paper addresses long-term and recent changes in the fisheries for smelt in the eastern Gulf of Finland, including both commercial and recreational fisheries, and the range of fishing gears used. The commercial smelt fishery is mainly conducted during the spawning period (April–May) on migrating fish, using trap nets of various designs and beach seines. There has been an increase in recreational fisheries for smelt; in years when ice cover on the gulf during winter (December–April) is steady, recreational fishers from St. Petersburg, using hook and line, may catch quantities that are comparable to those of commercial catches. Several factors may account for the stock dynamics and associated changes in catches of smelt: these include a decrease in prey availability in the gulf; loss and degradation of spawning and nursery habitats, partly associated with large-scale hydroengineering operations in Neva Bay; and illegal, unreported and unregulated (IUU) fishing which became widespread in post-Soviet decades. In spite of a gradual increase in smelt abundance in the most recent 15 years, a failure to accurately monitor and manage the extent of IUU and recreational fishing for smelt, to assess the status of the stock, or to forecast catches, increases the risk of overfishing of the spawning stock.     

Diplostomiasis in the sand smelt, Atherina presbyter (Cuvier), population at Fawley Power Station

Diplostomiasis, or black spot, is a disease of teleost fish, which results from the encystment of metacercarial larvae of digenean trematodes in the skin of the fish. This parasite occurs on sand smelt, Atherina presbyter , and pout, Trisopterus luscus , at Fawley. Since the debilitating effects of disease or parasitism may be a factor influencing fish impingement, the incidence of black spot in the Fawley sand smelt population has been studied. Fish 3 months old can be infected, and an average of 9% of the population up to 2 years old is infected. There is a rapid size-correlated rise in infection in 2 + fish, associated with their migratory habit. The metacercarial morphology has been examined, and it is tentatively identified as a species of Neodiplostomum . There is a greater settlement of metacercaria on the fins and the eye of the sand smelt than on the scaled parts of the body. No seasonality or change in levels of infection over the years 1977 to 1981 were found. The incidence of the parasite has no effect on the impingement of sand smelt at Fawley; the reasons for this are discussed. Models of the changing rate of infection with migration imply that the population associated with the power station is less infected than surrounding natural populations. The infection rates of diplostomiasis in separate populations of host fish may prove useful in distinguishing the origins of individuals in a mixed impingement on the power station screens.     

Diplostomiasis in sand smelt, Atherina presbyter Cuvier, from the Fleet, Dorset and its use as a population indicator

The population of sand smelt, Atherina presbyter , breeding in the Fleet, Dorset, shows a high infection of diplostomiasis. The population was studied in 1983 to clarify aspects for this parasitic condition previously analysed for the sand smelt population at Fawley, Southampton Water. All age classes showed a higher percentage infection and mean number of metacercaria per fish than at Fawley. Analysis of postlarvae and juveniles showed that infection can occur at 1 week old, and verified the hypothesis that the scales of older fish inhibit cercarial settlement. Circumstantial evidence suggests that Potamopyrgus jenkinsi may be the first vector host for this parasite, and the densities of this species and of nesting little tern colonies would account for the differential infection between these two sand smelt populations. The increase in infection of 2 fish at Fawley cannot be attributed to mixing with the Fleet population, and the different infection levels demonstrate population isolation. High levels of infection are limited to this part of the English Channel: sand smelt samples from around the coasts of the British Isles show minimal infection rates elsewhere and suggest a southerly distribution of the parasite, away from Atlantic oceanic waters.     

Spawning ecology of Japanese surf smelt, Hypomesus pretiosus japonicus (Osmeridae), in Otsuchi Bay, northeastern Japan

The spawning habits of Japanese surf smelt, Hypomesus pretiosus japonicus (Japanese name chika), were studied from 1992 to 1995 at Akaiso Beach in Otsuchi Bay off the Pacific coast of northern Honshu. Investigations were conducted in relation to time, tidal rhythm, sand grain size on the spawning ground, and sex and age of spawners. Spawning occurred from late March to early May with its peak at the spring tide period during full moon in April. Before dark, fish gathered to school from 1–3 m depth, and 10–20 m off the shoreline of the spawning beach. Just before dark, they repeatedly approached the shoreline and stayed near the shoreline to spawn just after dark. In the spawning process, three intervals, i.e. aggregation, approach, and spawning, were recognized and these intervals are thought to be functionally connected. Mating occurred in a unit or group formed by one female and several males. During 1992–1995, except for 1994, spawning took place in a restricted region of the beach where backwash was stronger than other areas, and most sand grains were more than 1 mm in diameter and coarser than those of other areas. Although spawning was observed near the shoreline (34 to 120 cm tide level), most of the eggs were dispersed by backwash and each became attached to a few sand grains close to a step formed at 1–2 m depth off the spawning site. Spawners were composed mainly of age 0+ fish and some 1+ fish. Males usually outnumbered females on the spawning ground. Their spawning styles are discussed in relation to their ecology and habitat.     

Sand smelt (Atherina boyeri) migration within the water system of the Camargue,southern France

In the coastal lagoons of Southern France, sand smelt Atherina boyeri, is known as a sedentary species. However part of the sand smelt population living in the brackish water Vaccarès lagoon in the Camargue annually migrates to fresh waters. The movements of sand smelts within the watersystem of the Camargue were studied from 1986 to 1990. Fish traps and fyke nets were set and catches were standardised to Catch Per Unit Effort (CPUE). A Stepwise Multiple Correlation analysis was carried out to link fish abundance with various environmental factors. Between September and November, sand smelts living in the Vaccarès start to colonize fresh waters (drainage canals and then temporary marshes), until March. Spawning occurs from April to June, both in the shallow branches of the canal and in the marshes. From June onwards adults and young-of-the year leave the fresh waters and return to the Vaccarès lagoon where they remain until the next migration. This autumnal migration to freshwater habitats involves mainly fish less than 3 years old, the oldest individuals remaining all year in the Vaccarès. Water level and photoperiod contribute to 20.7% of the variation of CPUE within the drainage canal, while date, water temperature, and rainfall combined, only account for 2.5% of CPUE variations. Date and photoperiod contribute significantly to explaining the patterns of fish migrations between the canal and the marshes. The density of mature sand smelt in the marshes before spawning, varies between 4 and 4346 fish ha^–1. Fry mortality (against number of eggs spawned) over the first two months of life was assessed to vary between 97.5% and 99.9%. Physiological factors such as osmoregulation linked to water temperature are possibly the ultimate factors explaining these unusual annual migrations of sand smelt in the Camargue.     

Fat cycling in the mosquitofish (Gambusia affinis): fat storage as a reproductive adaptation

Summary We argue, based on reviewed literature covering reptiles, amphibians, birds, and fish, that fat storage may represent a life history adaptation because it enables an organism to shift in time when resources are allocated to reproduction. We applied these arguments to fat and population cycles in three populations of the mosquito fish, Gambusia affinis. For males, there appeared to be a constant size at maturation during the reproductive season. Mature males became scarce late in the summer. At the same time, immature males delayed maturity and attained much larger sizes; they matured in large numbers in the fall. The amount of stored fat tended to be equal for immature and mature males at all times except in the late summer. In the August samples, when mature males were relatively rare, they also had the lowest level of fat reserves. It appears that the older generation of mature males did not store fat and did not overwinter. At the same time, immature males registered a two to three fold increase in fat reserves. These differences in fat content between mature and immature males disappeared by September, probably because of the recruitment of a new generation of mature males. The reserves were gradually utilized during the winter. Females reproduced from the late spring through mid- to late-summer. They stopped reproducing in the late summer, when there was ample time to produce an additional litter of young. There was an inverse relationship between resources devoted to reproduction and fat reserves. As reproductive allotment decreased in the late summer, fat reserves increased. The magnitude of the change in fat reserves was similar to that displayed by males. The reserves were depleted over the winter. Significant reserves remained at the beginning of the reproductive season the following spring. Reproducing females utilized the remaining reserves significantly more rapidly than non-reproducing females. An analysis of resource availability revealed an overall decrease in food availability in the late summer, coincident with the increase in fat reserves. These cycles are therefore not attributable to changes in resource availability. They instead indicate a change in how resources are allocated by the fish. The trends in the data indicate that fat reserves are used to shift investment in reproduction from the late summer to the following spring. In males, deferring maturity, rather than maturing in August, allows them to store the necessary reserves to survive the winter so that they can mate the following spring. In females, a subset of the fat reserves is intended for producing the first clutch of eggs the following spring. The female pattern corresponds to those reported for a diversity of organisms. The possible advantages of shifting reproductive effort from the fall to the following spring include higher fecundity and higher offspring fitness. The limitations of the methodology and potential directions for future research are discussed.     

Genetic structure and relationships among anadromous and landlocked populations of rainbow smelt, Osmerus mordax, Mitchill, as revealed by mtDNA restriction analysis

Larvae of anadromous rainbow smelt originating in various spawning tributaries are retained in the St Lawrence estuary. We proposed that these smelt represent one population genetically differentiated from adjacent populations characterized by geographically distinct larval retention areas. We also analysed four landlocked populations to evaluate the phylogenetic basis of dwarf and normal-sized phenotypes and their relation to an adromous smelt. A phylogenetic distinction was revealed between anadromous and landlocked smelt, with only one of the two mtDNA phylogenetic groups of anadromous fish observed among landlocked smelt. Significant geographical heterogeneity in the distribution of mtDNA genotypes was observed among landlocked smelt, suggesting that dwarfism in smelt may be polyphyletic in origin. St Lawrence smelt were genetically identical but distinct from adjacent populations, supporting the proposition that population genetic structure reflects the number of larval retention zones rather than spawning sites.     

Predation on adult Atlantic salmon, Salmo salar L., by otters, Lutra lutra (L.), within the River Dee system, Aberdeenshire, Scotland

Predation on adult salmon, Salmo salur L., by otters, Lurra lutra (L.), varied seasonally on the R. Dee, Aberdeenshire, Scotland, being highest during the spawning season in winter. Predation is described for some tributaries of the river. Male fish were caught by otters more often than females, and it is suggested that they were most vulnerable during their extensive excursions up and down stream, particularly as they negotiated shallow riffles. Otters appeared to prey upon healthy fish rather than those infested with Saprolegnia sp. but there was no difference in the size, freshwater- or sea-age offish killed by otterscompared with 'kelts' which had died non-violently. At least some of the otters obtained most of their daily food requirements by catching a single salmon per night.
Considerable numbers of adult salmon may be killed by otters during the spawning period but it is suggested that, because most are males, this is unlikely to affect the breeding success of the salmon population. Most predation occurs outside the fishing season and so is unlikely to reduce the numbers of salmon caught by anglers.     

The New Zealand common smelt: biology and ecology

The common smelt is one of the most widespread indigenous freshwater fishes in New Zealand. One other member of the family Retropinnidae, Stokellia anisodon (Stokell), is present but is confined to a small region of the South Island. There are many diadromous as well as river and lake resident populations, the latter, sometimes a result of introductions to serve as forage fish for trout. Diadromous smelt spawn during austral autumn–winter on sand bars of lower riverine reaches. Larval stages inhabit coastal marine waters, and the postlarvae to immature stages re‐enter rivers and some lowland lakes. Diadromous smelt are distinguished from lowland lake resident forms by high vertebral but low gill raker numbers and larger size and from those present in some isolated waters, by high vertebral numbers alone. Lake or reservoir resident smelt usually spawn in austral spring–summer on sandy shallows at stream mouths or along shorelines. Verified smelt ages (otolith analyses) indicate that in some populations most smelt mature and spawn after c. 1 year. Adult smelt feed on a spectrum of primarily invertebrate animals ranging from small zooplankters to insects and occasionally small fishes. Smelt are a major prey for both brown trout and rainbow trout. Adult smelt are a minor food for the Maori people. As postlarvae they are a component of a few 'whitebait' fisheries. Most smelt populations are increasingly affected by environmental changes induced by human activities. Although many studies have examined problems affecting smelt, further effort is required, along with more basic research.     

Behavioural studies on the lesser sandeel Ammodytes marinus (Raitt) III. The effect of temperature on activity and the environmental control of the annual cycle of activity

The behaviour of the lesser sandeel, Ammodytes marinus (Raitt), has been investigated at 5, 10 and 15° C, using a photographic method of recording activity. The activity patterns at 10 and 15° C were very similar, there being a high level of swimming activity during the light period, which fell to a low level at 5° C. It was also lower at 10° C at the end of the experiment than at the beginning and it is suggested that this might have been due to an increase in the fat contents of the fish. The feeding rate of the fish was measured and showed a Q ₁₀ of 2.08 for the temperature range 5–15° C. The annual cycle of activity of A. marinus is discussed in relation to seasonal changes in food availability, light and temperature, and in the fat content of the fish. It is concluded that after spawning in the December–January period the fish remain buried in the sand until April, because of the limiting effect on swimming and feeding activity of the environmental factors in the intervening period. The proportion of fish available for capture at the start of the fishery in April is related mainly to temperature, but food (as measured by numbers of copepods) light intensity and photoperiod are by then increasing rapidly. After July the fishery ceases and it is thought that this is because the fish have entered an overwintering stage, during which they remain buried in the sand. This phase is also thought to be associated with the maturation of the gonads in readiness for the winter spawning. The factors causing the fish to enter this stage are as yet undetermined but may be related to the attainment of a certain level of fat content.     

A bioenergetic assessment of the influence of stocking practices on rainbow trout (Oncorhynchus mykiss) growth and consumption in a New Zealand lake

Summary

• 1 To investigate the carrying capacity and factors affecting growth of rainbow trout in Lake Rotoiti, we employed a bioenergetics model to assess the influence of stocking rates, timing of releases and prey abundance on growth and prey consumption. We hypothesised that stocking rates and prey abundance would affect growth and prey consumption by influencing per‐capita prey availability, and that the environmental conditions encountered by fish at the time of stocking would affect growth and consumption.
• 2 Prey consumption of stocked rainbow trout was calculated with the Wisconsin bioenergetics model. We calculated growth trajectories of released trout based on data from stocked trout that were released in spring and autumn from 1993 to 2009 and then re‐captured by anglers. Diet, prey energy density, body mass lost during spawning and lake temperature were measured locally.
• 3 Stocking timing had no effect on return rates to anglers or length or weight of caught fish. Although trout released in autumn were smaller than those released in spring, autumn‐released trout grew at a faster rate and had similar lengths and weights to spring cohorts after 2 years of growth in the lake. Modelled consumption parameters were negatively correlated with trout population size, suggesting that stocking rates (347–809 fish ha^?1 year^?1) caused density‐dependent effects on growth. Although common smelt (Retropinna retropinna) accounted for 85% of total prey consumption, no significant relationship was found between prey consumption by individual trout and adult smelt abundance, possibly because trout are targeting smaller smelt that our abundance estimate did not account for.
• 4 Releasing trout in autumn appears to be advantageous for growth, possibly because (i) temperature is more suitable for growth in autumn–winter than in spring–summer and (ii) prey for small trout is abundant in autumn. Mild winter conditions appear to enhance overwinter survival and growth of rainbow trout in warm‐temperate lakes compared to higher latitudes. This implies that moderately productive warm‐temperate lake ecosystems are highly suitable for trout growth in winter, but less so in summer, when lake stratification and high nutrient levels may create conditions suitable for algal blooms and hypolimnetic deoxygenation. High growth rates of trout in warm‐temperate lakes can therefore be supported by timing releases to coincide with favourable winter conditions.

     

Spawning Dynamics and Size Related Trends in Reproductive Parameters of Southern Bluefin Tuna,Thunnus maccoyii

Knowledge of spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the spawning ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the spawning ground slightly later and depart earlier in the spawning season relative to large fish. All females were mature and the majority were classed as spawning capable (actively spawning or non-spawning) with a very small proportion classed as regressing. The fraction of females spawning per day decreased with fish size, but once females start a spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of spawning and non-spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the spawning ground as a function of fish size (if known) and demographic data for the spawning population to provide a time series of relative annual fecundity for SBT.     

Pond smelt <Emphasis Type="Italic">Hypomesus olidus</Emphasis>, a new species of the ichthyofauna of the Commander Islands

The population of pond smelt Hypomesus olidus has been registered for the first time in the water bodies of Bering Island (Commander Islands). The spawning of this species has been observed in the Sarannoe Lake system, and the maturing breeders have been caught in the freshwater-brackish Gavanskoe Lake system. The spawning grounds, the spawning period, the environment, and the morphology of the breeders have been described. The ratio of Ca and Sr isotopes in the otoliths of the pond smelt inhabiting the Sarannoe Lake system evidenced that this species here was presented by the resident ecotype. The problem of the smelt phylogeny and resettlement in the northern Pacific Ocean is discussed.     

Assessment of body condition in live birds; measurements of protein and fat reserves in the mute swan, Cygnus olor

Condition in animals is often measured in relation to various demands, such as reproduction, migration and cold weather. Usually, indices of protein and fat reserves have to be measured on dead animals. Measurements on live animals enable variations in the condition of individuals to be monitored over time, and can be related to their life histories.
In birds, the size of the breast muscle is the most commonly used measure of protein reserves. A technique for measuring breast muscle thickness was developed, using ultrasound, and was tested on mute swans. The measurements were accurate and highly repeatable. Breast muscle thickness was positively related to the lean dry weight of the breast muscle, and is likely to be a good indicator of total protein reserves.
A system of fat scoring by colour was developed to assess the size of the subcutaneous fat layer. Although the method relies on subjective judgements, the results were highly correlated with the percentage of fat in the subcutaneous layer, and with other measures of fat reserves.
Measurements were made on live, non-breeding swans to monitor seasonal variations in reserves. The seasonal pattern of fat reserves was similar to the normal cycle of weight changes; high in winter and low in summer. There was no change in relation to the moult. No distinct seasonal variation in muscle thickness was found.
There is an unusual pattern of change in the relative size of reserves during emaciation in swans. Muscle reserves appear to be depleted to a greater extent than fat reserves. This is possibly due to the effects of lead poisoning, causing protein necrosis and preventing muscle regeneration.     

Seasonal variation in ornament expression,body size,energetic reserves,immune response,and survival in males of a territorial insect

Abstract 1. Seasonal variation in immune response has rarely been investigated in invertebrates and, therefore, we have studied this using territorial adult males of the damselfly, Hetaerina americana (Fabricius), in several generations, for a year and a half. 2. We investigated and related seasonal variation in red pigmented wing spot size (an ornamental trait) and body size to fat reserves using four immunity components – melanisation ability, phenoloxidase (PO) and nitric oxide (NO) activity, and haemolymph protein concentration – and survival ability after a bacterial immune challenge. 3. There was seasonal variation in spot expression, being more intense in the non‐winter months and less intense in winter months, and, to some extent, a similar pattern was found for NO. Although there was also variation in melanisation, PO activity, protein concentration and fat reserves, this was not consistently related to variation in spot size. Survival was lower in the winter than in non‐winter months. 4. Animals with larger spot and body size had greater values of melanisation, PO and NO activity, and protein concentration. The relation of spot and body size with fat reserves is still not clear. 5. Unlike other studies, ornament was not similarly correlated with all typical immune components (at best, mainly NO). 6. Similar to what occurs in vertebrates, survival is lower during the winter months. In the case of vertebrate studies, however, the same individual suffers these changes. In the American rubyspot, distinct cohorts demonstrated seasonal differences.     

Size‐related and diel variations in microhabitat use of three endangered small fishes in a Mediterranean coastal stream

This study analysed the microhabitat use of three endangered fish species, Andalusian toothcarp Aphanius baeticus , Iberian loach Cobitis paludica and sand smelt Atherina boyeri , in a coastal stream stretch. Plastic minnow traps were set both during daytime and at night on the bottom and at the surface. Depth and presence of effective refuge were recorded for each trap. To assess size‐related changes in microhabitat use individuals of each species were classified in three size classes. The three species preferentially used bottom positions in the water column, though this behaviour was more evident in the case of Iberian loach. While large Iberian loach remained active at night Andalusian toothcarp and sand smelt were strongly diurnal, especially larger individuals. The three species showed a clear ontogenetic change in microhabitat preferences towards deeper waters. Small Andalusian toothcarp and medium‐sized Iberian loach used deeper microhabitat in the presence of refuge. Large Andalusian toothcarp consistently preferred exposed microhabitat at any time. Andalusian toothcarp using refuge were smaller at any time, while Iberian loach followed this pattern only at night. The differential vulnerability of these species to different predators (aerial and aquatic; diurnal and nocturnal) could explain the observed patterns in microhabitat use. Fish tended to co‐occur in microhabitats either due to habitat characteristics independently of species or due to species independently of habitat. Andalusian toothcarp segregated spatio‐temporally from sand smelt and Iberian loach, but these species occurred independently of each other. According to these co‐occurrence patterns, Andalusian toothcarp would be more sensitive than Iberian loach or sand smelt to interspecific interactions.     

The biology of Boyer's sand smelt, Atherina boyeri Risso in the Bardawil Lagoon on the Mediterranean coast of Sinai

The present study describes some aspects of the life history of Boyer's sand smelt Atherina boyeri in the hypersaline Bardawil Lagoon on the Mediterranean coast of the Sinai peninsula, Egypt. Monthly samples were collected with a small-mesh experimental beach-seine during the years 1973–1974. Age determinations were based on otoliths readings and length frequency distributions which indicate that the Bardawil Lagoon population consists mostly of 0-age group. The largest recorded fish was 63 mm in standard length (S.L.). Length-weight relationship has been calculated as: W = 13.7 × 10⁻⁶× L ^2.93 where W = weight (g) and L =S.L. (mm). Atherina boyeri mature at the length of 34 mm. Spawning takes place from March to September. The average number of eggs in the ovary of a ripe female at the beginning of the spawning season was found to be 522. Females of all sizes were more numerous than males. In immature fish, less than 34 mm long, females constituted 53% of the population. In larger fish the number of females was higher; in fish over 34 mm long females constituted 64% and in fish over 51 mm—96%. Atherina boyeri in the Bardawil Lagoon feeds on both zoobenthos and zooplankton, mainly amphipods and copepods. Polychaetes, mysidaceans, insects and fish were also represented. Atherina boyeri is the host of endoparasitic Trematoda, Acanthocephala and Nematoda. The examined fish were found to have metacercaria in their mesenteries and liver.