The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

Morphometric analysis of orange roughy (Hoplostethus atlanticus) off the continental slope of southern Australia

Morphometric variation was used to examine the stock structure, in southern Australian waters, of the deepwater marine teleost Hoplostethus atlanticus , orange roughy. Seven samples were collected from non-spawning aggregations in 1989–1990. Three samples were also collected in the winter of 1992, two from the main spawning site off the eastern coast of Tasmania (St Helens), and the third from the other main fishing ground south of Tasmania. The 38 morphometric measurements taken from each of over 1300 fish were size-standardized by an allometric formula and analysed by univariate and multivariate statistics. The results indicate significant variation in the morphology of orange roughy caught from geographically distinct aggregations. They further suggest that the main spawning aggregation may consist of fish from different groups at different times of the spawning period. There appear to be at least seven morphologically distinguishable stocks of orange roughy in southern Australian waters, despite genetic data indicating appreciable levels of gene flow between them.     

The influence of maternal length and age on the size and weight of the eggs and the relative fecundity of the haddock, Melanogrammus aeglefinus, in British waters

The diameter and dry weight of the eggs of haddock, Melanogrammus aeglefinus , are positively correlated with fish length. The correlations are largely due to the fact that many of the smaller fish that were sampled were 2 years old, and the eggs of these young haddock, which can be regarded as precocious spawners, are significantly smaller and lighter than those of older fish. The relative fecundity of 2–year–old haddock (274 eggs g⁻¹) is also lower than that of the other age classes (493 eggs g⁻¹); this has important implications for the estimation of egg production from female spawning stock biomass. It is pointed out that in some years precocious spawners represent a large component of the North Sea haddock spawning stock. When the annual egg production of this stock is calculated, it may be appropriate to apply a weighting factor to the number of eggs contributed by the 2–year–olds, on the assumption that the small eggs of these fish produce larvae that are less viable than those of older haddock.     

Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley

The reproductive biology of the Oxleyan pygmy perch Nannoperca oxleyana is described from simultaneous studies of wild populations in north-eastern New South Wales and mature fish held in aquaria. In the wild, 50% of males and females matured at total lengths of 24·0–25·9 and 28·0–29·9 mm, respectively. The species displays sexual dichromatism during the spawning season, with males developing more intense red and brown fin and body colouration, and black pelvic fins. Captive male broodfish displayed territoriality during the breeding season, closely guarding sites within artificial, plant-like substrata in which pairs of fish spawned adhesive eggs. Protracted serial spawning of wild and captive fish occurred from September to April and May at mean water temperatures ≥16·6° C and day length ≥10·7 h. Captive broodfish spawned on an average of 57% of days during the 256 day spawning period. Gonado-somatic indices averaged 0·7% for all ripe males and 4·1–4·2% for all ripe females collected. Mean total and batch fecundities of captive females were 1323 eggs per fish and 7·8 eggs per fish per day, respectively, and relative fecundity was 587 eggs g⁻¹ of body mass. Batch fecundity of wild females was estimated at 7·8 eggs per fish. The adaptive significance of this reproductive strategy in a harsh, variable environment is discussed.     

Seasonal variation in egg production and batch fecundity of European hake Merluccius merluccius (L.) in the Bay of Biscay

Sexually mature female hake Merluccius merluccius with hydrated ovaries were sampled on a monthly basis in the Bay of Biscay, from May 1996 to October 1997 and from March to April 1998. The batch fecundity was positively related to total length. The relative batch fecundity ( F _Brel) varied significantly among months and years, but not between areas, i.e. International Council for the Exploration of the Sea Divisions VIIIa and VIIIb within the Bay of Biscay. Two levels of F _Brel were found in 1997: the highest between January and April (mean ± s . e . 167 ± 5 eggs g⁻¹) and the lowest from May to October (112 ± 3 eggs g⁻¹). Population condition factor and gonado-somatic indices ( I _G) followed the expected trend in relation to the monthly changes in F _Brel during 1997. The F _Brel variation between years was 9% for 1996–1997 and 28% for 1997–1998, and the difference of the I _G was c. 14 and 36%, respectively. Population relative egg production varied from a high value in January to March (985 eggs g⁻¹) to a low egg production between April and October 1997 (445 eggs g⁻¹).     

Size-dependent mortality of red sea bream, Pagrus major, juveniles released with fluorescent otolith-tags in News Bay, Japan

Totals of 2^.67 x 10⁵ and 7^.56 x 10⁵ juvenile red sea bream of three size groups (10, 20 and 40 mm t.l.) marked with a fluorescent substance in the otolith were released in News Bay, Oita Prefecture, Japan, in July 1987 and June 1988, respectively; the aim was to estimate growth and mortality of different developmental stages.
Of fish released in 1987 and 1988, 10 618 and 4413, respectively were recaptured during those two years. Released fish remained in the bay until the end of summer, and afterwards migrated out towards open waters. Fish of the 40-mm group released in 1987 grew to over 200 mm t.l. in one year. Mean growth rate for 19 days after release was higher in the 40-mm group (0^.87 mm day⁻¹) than in the 20-mm group (0^.74mm day⁻¹). Survival rates over 19 days were 59^.0 and 10^.1 % for 40-mm and 20-mm fish, respectively, in 1987, and those over 30 days were 69^.2, 3^.3 and 0^.0% for 40-mm, 20-mm and 10-mm fish, respectively, in 1988.
Cannibalism was indicated by the presence of marked otoliths for 20-mm fish in the stomachs of a few 40-mm individuals recaptured 2 days after release. Size-dependent growth and size-selective mortality were both noted in juvenile red sea bream, i.e. the relative size differential between larger and smaller individuals was maintained in the period between marking and recapture, and mortality was inversely proportional to size.     

Relationship of plasma steroids to germ cell development and the presence of protamine mRNA in rainbow trout during the induction of spermatogenesis with partially purified salmon gonadotropin

The gonadosomatic index (GSI) of pre–pubertal male rainbow trout, which had been injected biweekly with partially purified salmon gonadotropin (sG–G100, 50 μ mUg kg⁻¹ body weight), increased from 0.05 to 1.85 over 21 weeks from injection, while control GSI remained below 0.05. Plasma testosterone (T) increased from 2 to 11.34 ng ml⁻¹ by week 21 in injected fish, while control level remained below 1.5 ng ml⁻¹. In injected fish plasma 11–ketotestosterone (KT) and 17,20–dihydroxyprogesterone (17α20βP) levels increased from 20.2 to 41.9 and 8.9 to 219.7 ng ml⁻¹ respectively. Plasma T, 11–KT, and 17α20βP were all correlated with the GSI ( P <0–001) in injected fish. The most advanced stage of germ cells present in the control fish were spermatogonia. However, in injected fish spermatozoa were present by week 21. Eggs fertilized at this time with spermatozoa from injected fish achieved a 78% fertilization rate, whereas the testicular homogenate was incapable of fertilizing eggs.     

The population biology of pike, Esox lucius L., in two gravel pit lakes, with special reference to early life history

The population biology of pike in two gravel pit lakes of contrasting habitat type were studied. The density of pike (1 + and over) in November 1987 in the Main Lake was 7.7 fish ha⁻¹ (19 kg ha⁻¹) and in St Peter's was 71 fish ha'(53 kg ha⁻¹). The age distribution showed that recruitment was consistent in St Peter's but variable in the Main Lake. The main factor causing this difference in recruitment is abundance of aquatic vegetation. Survival up to November 1987 of 0-group pike in the Main Lake was 0.00175% from potential egg deposition, producing 6.6 fish ha⁻¹ (0.83 kg ha⁻¹). In St Peter's survival was 0.00315%, producing 23 fish ha⁻¹ (3.04 kg ha ¹).     

Some aspects of the biology of a cyprinid, Aspius vorax Heckel

Scales were used for the determination of age with back-calculation of length. The oldest fish was VII + years old. Back-calculation did not exhibit Lee's phenomenon. The most rapid growth occurred in summer at water temperatures over 25°C. The growth in weight was c . 331 g year^-1 after IV vears of life. Growth was well described by von Bertalanffy equation : l_l - 91·0 [ l= ^{0·122(l0·25)}] The length-weight relationship followed the cube law (b = 3·0601) K_n ranged from 0·74 to 1·18 with a mean value of 1·0. Spawning occurred in January, fecundity was 74 509 with a mean of 1157 eggs -¹ body weight. Mean diameter of eggs was 1071 (pm). A developed ovary had ova of two sizes, immature oocytes and mature ova. The fish is a carnivorous feeder.     

The biology of stone loach Barbatula barbatulus in the Rivers Goloustnaya and Olkha, East Siberia

Five hundred and four stone loach 63–202 mm in total length, of I + to 8 + age groups, were sampled in two rivers of East Siberia from April to October 1989–90. This paper presents data on the seasonal dynamics of fecundity, ripening, fatness and feeding intensity. A second spawning from the end of August to October has been identified for the first time for this species. The absolute fecundity ranged from 1710 to 27600, and the relative fecundity varied from 216 to 833 eggs g⁻¹: (fish weight). Stone loach in the River Olkha grew faster than those in the River Goloustnaya and, according to this index, are closer to stone loach from streams of northern England.     

Reproduction in the greenback grey mullet, Liza subviridis (Valenciennes, 1836)

This paper presents data on the reproductive biology of Liza subviridis , a little studied mullet species. The fish is heterosexual, exhibiting external fertilization. Six maturity stages can be macroscopically identified in the testes and seven in the ovaries. The macroscopic changes in the gonads are manifestations of histological changes occurring in the development of sperm cells and oocytes. First sexual maturity is attained in the length ranges of 9.5–11.5 cm and 10.5–11.5 cm in male and female fish respectively. The fecundity for fish measuring 10.3–13.9 cm in standard length ranged from 40 000–145 000 eggs. The relationship between fecundity ( F ) and length ( L ) can be represented as: F = 1.9044 L ^4.2998. The spawning duration in L. subviridis is restricted to a short and definite period, with all ripe ova being released within a single spawning act. A pronounced spawning season can be detected to extend from June to November. However, during off-seasons, some spawning also occurs. The correlations between spawning, rainfall and air temperature is discussed.     

Fecundity and Maturity of Orange Roughy (Hoplostethus atlanticus Collett 1889) on the Porcupine Bank, Northeast Atlantic

Synopsis The first, comprehensive analysis of the fecundity and reproductive maturity of orange roughy, Hoplostethus atlanticus, from a specific area in the Northeast Atlantic is reported. Specimens were collected from aboard vessels, targeting this species on the Porcupine Bank (ICES subarea VII), in waters of between 1400 m and 1,650 m depth. Between September and December 2002, a non-random, stratified, sampling protocol was implemented by on board fisheries biologists to collect mature female fish between 300 mm and 540 mm SL. Ovaries from 65 individuals, representing the majority of 10 mm SL size classes, formed the analytical sample. A novel, digital method of oocyte counting was developed, allowing digital images of oocytes to be annotated, counted and stored. Total fecundity ranged between 20,352 and 244,578 oocytes per female and mean total fecundity was estimated to be 97,368 oocytes per female (SD = 48,322). Relative fecundity was estimated to be 33,376 oocytes per kg (SD = 11,407). Fecundity was shown not to decrease with age. Macroscopic analyses showed that 50% of females were not mature until they reached 27.5 years and 37 cm SL. Comparison with stocks from the southern hemisphere indicate that orange roughy from the Northeast Atlantic mature at a larger size and generally have a higher mean fecundity than those found in the southern hemisphere. This may reflect differences in growth rates influenced by environmental variables and fishing pressure.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.     

Some effects of low pH and calcium on the growth and tissue mineral content of yearling brown trout, Salmo trutta

Yearling brown trout, Salmo trutta , were exposed to low mineral content water (nominal concentrations of 20μmol 1⁻¹ magnesium, 7.7 μmol 1⁻¹ potassium, 44 μmol 1⁻¹ sodium) over a pH range of 4.0–5.2 with ambient calcium concentrations of 2.5–60 μmol 1⁻¹. All fish died at pH 4.0 and 4.2 irrespective of ambient calcium concentration and also at pH 4.4 with only 2–3 μmol 1 ⁻¹ calcium (that is calcium-free water except for that leached from the diet or excreted by the fish). Good growth rates were obtained over the remaining treatments which extended down to pH 4.4 with as little as 7 μmol 1⁻¹ calcium. When starved, weight loss was inversely correlated with pH. Effects on plasma chloride, percentage dry weight and calcium, potassium sodium, and phosphorus contents of skin, muscle and bone tissue were also investigated. These demonstrated pH effects on mineral metabolism in starved fish, but no effects were detected in fed fish.     

Batch fecundity of Atlantic mackerel, Scomber scombrus L.

The total annual fecundity of mackerel, Scomber scombrus L., during a spawning season is produced by release of discrete batches of eggs. Total fecundity is then the product of the number of batches times the batch fecundity ( F _bw). An extensive trawl survey of the Western mackerel stock in the NE Atlantic was undertaken in the 1989 spawning season. Batch fecundity was estimated for 298 fish by counting hydrated eggs in ovaries just prior to ovulation. F _bw, expressed as eggs g⁻¹ body weight, varied with latitude: south of 51°N, F _bw= 55.49, s.e. = 2.04, n = 227; between 51°N and 55°N, F _bw= 45.72, s.e. = 3.41, n = 52 and north of 55° N, F _bw= 41.33, s.e. = 5.52, n = 19. It is suggested that as spawning fish migrate northwards the batch size decreases with progress of the spawning season.     

Normal ranges of some blood chemistry parameters in adult farmed Atlantic salmon, Salmo salar

Blood samples from healthy adult Atlantic salmon fed an optimal diet in net sea pens were collected at intervals from October to May. Haematological determinations and biochemical serum analyses were carried out on 20 fish in each of seven samples. The ranges of haemato-logical values for sample means were: haematocrit 44–49%, haemoglobin 8.9–10.4 g 100ml⁻¹, red blood cell count 0.85–1.10 × 10¹² l⁻¹, MCV 441–553 × 10⁻¹⁵ 1, MCH 94–106 × 10⁻⁶ g, MCHC 19.4–21.7 g 100ml⁻¹ and leucocrit 0.43–0.96%. The ranges of enzyme activities in serum, for sample means, were: alkaline phosphatase 647–988Ul⁻¹, aspartate aminotrans-ferase 202–351 Ul⁻¹ and alanine aminotransferase 4–8 Ul⁻¹. The ranges of the other parameters analyzed in serum were: total protein 41.6–56.6 gl⁻¹, albumin 18.3–24.3 gl⁻¹, albumin/total protein ratio 39.3–44.0%, creatinine 26–46 μmol, triglycerides 2.53–4.98 μmol and cholesterol 9.3–12.8 μmol. These values are considered to be the normal ranges in healthy fish. Variations due to seasonal changes, and the clinical significance of the selected parameters, are discussed. Data showing the reproducibility of the biochemical analyses in serum are presented.     

The effect of beet cyst nematode, Heterodera schachtii, on the yield of sugar beet in organic soils

In ten experiments on commercial sugar-beet crops grown on organic soils in 1984–86, a Genstat programme was used to examine the relationship between the initial population of Heterodera schachtii and sugar-beet root yield using the equation
Y = Ymin + (Ymax - Ymin) Z^pi-T
Fixing T = 200 eggs + juveniles 100 g^-1 soil and Z^T= 0.95, estimated values of Ymax varied from 49.2–67.1 t ha^-1 (129– 155% of the national average root yield for the years in which the experiments were carried out) and estimates of Ymin varied from 14.5–53.9 t ha^-1 (27–94% of Ymax). The estimated average root yield loss caused by the nematode was 6.95 t ha^-1.     

Fish production in the Jarama River, Central Spain

Fish production was estimated at three sites on the Jarama River, a small, typical upland river in Central Spain. Population estimates were made by the successive removal method of electrofishing. The same six species were recorded at each of the sites: Chondrostoma polylepis, Barbus barbus bocagei, Leuciscus cephalus pyraenaicus, Salmo trutta m. fario, Gobio gobio and Cobitis paludicola , with the first three species always dominant. Density, biomass, production (assuming that N_o is the total number of eggs spawned), and available production were, respectively: 13502-85776 ind. ha⁻¹, 178.6–221.3 kg ha⁻¹, 221.7–583.6 kg ha⁻¹ yr⁻¹, 118.1–271.9 kg ha⁻¹ yr⁻¹. Production estimates based on mortality curves were 7.9–19.5% (mean: 13.7) lower than those based on estimated from the number of eggs laid. Production per unit of area was highest at the widest and deepest site. Brown trout production contributed only 2–4% of the total production for all sites.     

The muscle twitch and the maximum swimming speed of giant bluefin tuna, Thunnus thynnus L.

Sustained swimming of bluefin tuna was analysed from video recordings made of a captive patrolling fish school [lengths (L) 1.7–3.3 m, body mass (M) 54–433 kg]. Speeds ranged from 0.6 to 1.2 L s⁻¹ (86–260 km day⁻¹) while stride length during steady speed swimming varied between 0.54 and 0.93 L. Maximum swimming speed was estimated by measuring twitch contraction of the anaerobic swimming muscle in pithed fish 5 min after death. Muscle contraction time increased from the shortest just behind the head (30–50 ms at 20% L) to the longest at the tail peduncle (80–90 ms at 80% L) (all at 28°C). A fish (L = 2.26 m) with a muscle contraction time of 50 ms at 25% L can have a maximum tail beat frequency of 10 Hz and maximum swimming speed of 15m s⁻¹ (54km h⁻¹) with a stride length of 0.65L. With a stride length of 1 L a speed of 22.6 m s⁻¹ (81.4 km h⁻¹) is possible. Power used at maximum speed was estimated for this fish at between 10 and 40 kW, with corresponding values for the drag coefficient at a Reynolds number of 4.43 × 10⁷ of 0.0007 and 0.0027.     

The production of brown trout, Salmo trutta in tributaries of the Upper Wye, Wales

The population density, age structure, biomass, growth and production of brown trout were investigated in four tributaries of the upper River Wye. The populations at each site were largely maintained by immigration from nursery areas. Abundance of separate year classes at sites on the three largest tributaries reached a peak at age 2+. On the smallest stream numbers reached a peak at 1+. Recruitment occurred throughout the year but decreased with age of year classes. Maximum O+ densities ranged from 0.04 to 0.89 m⁻², and >0+ densities from 0.13 to 0.59 m⁻². Average total biomass in 1975 ranged from 2.6 to 14.2 g m⁻². Within the study sites annual trout production in 1975 ranged from 2.9–19.7 g m⁻². Production values were dependent on age structure and population mobility at the study sites. In the three largest streams 2+ and 3+ fish contributed 66.3–88.3% of total production whilst 1+ and 2+ fish contributed 74.5–84.5 % of the total in the smallest stream. The mobile (non-resident) component of the population accounted for up to 60–70% of production at certain times of the year, but over the year (1976) accounted for =30 % of total production. The resident component of the highest annual production value (19.7 g m⁻²) was estimated to be between 15.0 and 18.2 g m⁻².