Distribution, growth, diet and foraging behaviour of the yellow-fin notothen Patagonotothen guntheri (Norman) on the Shag Rocks shelf (Southern Ocean)

The distribution, total length ( L _T) frequency and diet of Patagonotothen guntheri are described from 14 bottom trawl surveys conducted on the Shag Rocks and South Georgia shelves in the austral summers from 1986 to 2006. Patagonotothen guntheri (80–265 mm L _T) were caught on the Shag Rocks shelf from depths of 111 to 470 m, but no specimens were caught on the South Georgia shelf. Multiple cohorts were present during each survey and L _T-frequency analysis of these cohorts suggests that growth was slow (von Bertalanffy K = 0·133). Evidence from stomach contents and acoustic data (2005 and 2006) showed that P. guntheri is primarily a pelagic feeder, migrating from the sea floor towards the surface to feed during daylight. The diet of smaller fish (<140 mm) was dominated by copepods, predominantly Rhincalanus gigas , whilst larger fish principally consumed the pelagic hyperiid amphipod, Themisto gaudichaudii and Antarctic krill Euphausia superba . Some larger fish also took benthic prey.     

The biology of the bigeye grenadier at South Georgia

The biology of the bigeye grenadier Macrourus holotrachys caught as by‐catch in the Patagonian toothfish Dissostichus eleginoides longline fishery conducted around South Georgia was investigated to improve data available for fisheries management. Age estimates suggest that M. holotrachys is a moderately slow growing species ( K  = 0·10), reaching ages of >30 years and attaining total lengths ( L _T) >80 cm ( L _∞ = 33). The size at which 50% of females had started to mature ( L _int50) for M. holotrachys was 21 cm pre‐anal length ( L _PA) and occurred at c . 9 years old. Estimates of natural mortality and Pauly's growth performance index were found to be low ( M  = 0·09 and Φ = 2·82 respectively). Gonad maturity stage was described from macroscopic and histological investigation. Mature ovaries had oocytes at all developmental stages with between 22 and 55% likely to be spawned each year. Absolute fecundity ranged from 22 000 to 260 000 eggs and was positively correlated with both pre‐anal length and mass. A highly skewed sex ratio of 32 : 1, females : males, was found for specimens caught by longlines but not for a small sample of shallower trawl‐caught specimens. It is suggested that females are far more susceptible to longline capture than males. Macrourus holotrachys is a bentho‐pelagic predator and scavenger that feeds on a wide range of fishes and invertebrates. The fish are long lived, slow‐growing species typical of deep‐water grenadiers; fisheries management strategies should reflect their probable susceptibility to overfishing.     

The reproduction, age and growth of the spotted rockling

Biology of the Macaronesian endemic rockling Gaidropsarus guttatus was studied in the Azores. The overall sex ratio from the samples was highly in favour of females (1 : 6·33). The growth parameters were L _∞ = 24·23, k  = 1·219 and t ₀ = −0·059. Fish matured at 15 cm L _T and the spawning season was strongly clustered in April.     

Reproductive biology of the milk shark Rhizoprionodon acutus and the bigeye houndshark Iago omanensis in the coastal waters of Oman

Female Rhizoprionodon acutus were found to mature between 62 and 74 cm total length ( L _T) whereas males matured between 63 and 71 cm L _T. The L _T at 50% maturity was 64·3 cm for females and 64·7 cm for males. Litter size varied from one to six embryos, and was positively correlated with maternal L _T. Female embryos outnumbered males by a ratio of 2·3:1. The size at birth was c . 37 cm L _T. Full‐term embryos and post‐partum females were observed during all seasons although their occurrence was highest in spring. Spermatozoa were rarely recorded in the oviducal gland, indicating that this species does not store sperm. It was not possible to generate maturity curves for Iago omanensis but it was evident that females matured by the time they reached 35 cm and males were mature by 31 cm L _T. This species displayed a clearly defined reproductive cycle with parturition occurring primarily in spring, after a gestation period of c . 1 year. Maximal embryo size was 19 cm L _T while maximal litter size was 24 embryos. The oviducal gland appeared to act as a seminal receptacle and it appeared that females may utilize these stores by not mating every year.     

Life‐history variation among local populations of Atlantic cod from the Norwegian Skagerrak coast

Small‐scale spatial variation in life history was found among genetically distinct local populations of Atlantic cod Gadus morhua from the Norwegian Skagerrak coast. Among populations, age at 50% maturity varied from 2·6 to 3·8 years, total ( L _T) length at 50% maturity from 35 to 60 cm, annual survival from 33 to 64%, mean L _T at age 4 years from 43 to 63 cm, and mean backcalculated L _T at age 1 year from 8 to 12 cm.     

Early growth and juvenile population structure of lemon sharks Negaprion brevirostris in the Atol das Rocas Biological Reserve, off north‐east Brazil

Lemon sharks Negaprion brevirostris were sampled in the Atol das Rocas, a nursery area, on nine occasions from March 1999 to October 2003, during which 157 individuals were tagged and 35 were recaptured. The male : female sex ratio of captured individuals was 1 : 1·12. Mean ±  s . d . growth rates were 24·7 ± 3·4 cm year⁻¹ in total length ( L _T), 20·7 ± 3·2 cm year⁻¹ in fork length, and 19·5 ± 2·7 cm year⁻¹ in precaudal length. There was no significant difference in growth rates between males and females. Mean ±  s . d . increase in mass was 2565 ± 762 g year⁻¹. The von Bertalanffy growth parameters estimated by the Fabens method based on L _T were: k  = 0·077, L _∞ = 399·9 cm and t ₀ = −2·16. Despite the large variation of environmental conditions, particularly of tidal range and currents, and the lack of protective mangrove cover in the nursery area at Atol das Rocas, juvenile lemon sharks grew relatively faster than at other nurseries. Such rapid growth could be a response to abundant food availability or high risk of predation by adults that enter the nursery area.     

A histological study on the development of the digestive system of Pseudosciaena crocea larvae and juveniles

The ontogenetic development of the gut and accessory organs in large yellow croaker Pseudosciaena crocea was investigated using light microscopy from hatching up to the juvenile stage (40 days post hatch, dph). At 3 dph (mean ±  s . d ., 4·1 ± 0·1 mm total length, L _T), coinciding with the buccopharynx opening, larvae started to feed exogenously, and the gut consisted of a well‐developed buccopharynx, a partially‐differentiated oesophagus and an intestine divided in three regions (anterior intestine, intermediate intestine and rectum). Yolk reserves were not completely depleted at the onset of exogenous feeding, and a period of mixed nutrition was observed up to 6 dph (4·3 ± 0·1 mm L _T), when yolk was definitively exhausted. Important morphological changes occurred at the end of the larval period, coinciding with metamorphosis. At 17 dph (6·8 ± 0·6 mm L _T), pyloric caeca differentiated at the junction of the pyloric stomach and the anterior intestine. Gastric glands were first observed at 21 dph (9·2 ± 1·2 mm L _T), coinciding with the morphological development of the stomach in three different regions (cardiac, fundic and pyloric) according to the histological characteristics of their mucosa. At this age, large longitudinal folds appeared in the median and posterior oesophageal mucosa. These morphological and histological features suggested the achievement of a digestive system characteristic of large yellow croaker juveniles and adults.     

Diet of brown trout in relation to variation in abundance and size of pelagic fish prey

The seasonal diet of a predator, brown trout Salmo trutta [total length ( L _T) 17–69 cm] and simultaneous density and size‐structure of prey populations, vendace Coregonus albula and smelt Osmerus eperlanus (4–16 cm L _T), in a large boreal lake were analysed and compared in 2001 and 2002. The upper L _T limit for consumed prey was c . 40% of the predator L _T. All brown trout, however, preferred small (<10 cm L _T) and avoided large (≥10 cm L _T) prey. The results also suggested that equal densities of similar‐sized (4–10 cm L _T) fish of the two prey species led to random foraging on these species by brown trout, but if either one of the prey species predominated (>50%) in the lake, brown trout shifted to foraging on this species almost exclusively. Brown trout diets thus reflected the density dynamics of the two alternative prey species.     

Endurance swimming of European eel

A long‐term swim trial was performed with five female silver eels Anguilla anguilla of 0·8–1·0 kg ( c . 80 cm total length, L _T) swimming at 0·5 body lengths (BL) s⁻¹, corresponding to the mean swimming speed during spawning migration. The design of the Blazka‐type swim tunnel was significantly improved, and for the first time the flow pattern of a swim tunnel for fish was evaluated with the Laser‐Doppler method. The velocity profile over three different cross‐sections was determined. It was observed that 80% of the water velocity drop‐off occurred over a boundary layer of 20 mm. Therefore, swim velocity errors were negligible as the eels always swam outside this layer. The fish were able to swim continuously day and night during a period of 3 months in the swim tunnel through which fresh water at 19° C was passed. The oxygen consumption rates remained stable at 36·9 ± 2·9 mg O₂ kg⁻¹ h⁻¹ over the 3 months swimming period for all tested eels. The mean cost of transportation was 28·2 mg O₂ kg⁻¹ km⁻¹. From the total energy consumption the calculated decline in fat content was 30%. When extrapolating to 6000 km this would have been 60%, leaving only 40% of the total energy reserves for reproduction after arriving at the spawning site. Therefore low cost of transport combined with high fat content are crucial for the capacity of the eel to cross the Atlantic Ocean and reproduce.     

Effects of temperature, body size and feeding on rates of metabolism in young‐of‐the‐year haddock

The mean rate of oxygen consumption (routine respiration rate, R _R, mg O₂ fish⁻¹ h⁻¹), measured for individual or small groups of haddock Melanogrammus aeglefinus (3–12 cm standard length, L _S) maintained for 5 days within flow‐through respiratory chambers at four different temperatures, increased with increasing dry mass ( M _D). The relationship between R _R and M _D was allometric ( R _R = α  M ^b ) with b values of 0·631, 0·606, 0·655 and 0·650 at 5·0, 8·0, 12·0 and 15·0° C, respectively. The effect of temperature ( T ) and M _D on mean R _R was described by     indicating a Q ₁₀ of 2·27 between 5 and 15° C. Juvenile haddock routine metabolic scope, calculated as the ratio of the mean of highest and lowest deciles of R _R measured in each chamber, significantly decreased with temperature such that the routine scope at 15° C was half that at 5° C. The cost of feeding ( R _SDA) was c . 3% of consumed food energy, a value half that found for larger gadoid juveniles and adults.     

The effect of temperature and acclimation period on repeat swimming performance in cutthroat trout

Hatchery cutthroat trout Oncorhynchus clarki clarki were used to examine the effects of 48 h and 3 week temperature acclimation periods on critical swimming speed ( U _crit). The U _crit was determined for fish at acclimation temperatures of 7, 14 and 18° C using two consecutive ramp‐ U _crit tests in mobile Brett‐type swim tunnels. An additional group was tested at the stock's ambient rearing temperature of 10° C. The length of the temperature acclimation period had no significant effect on either the first or the second U _crit( U _crit‐1 and U _crit‐2, respectively) or on the recovery ratio (the quotient of U _crit‐2  U _crit‐1⁻¹). As anticipated, there was a significant positive relationship between U _crit‐1 and temperature ( P  < 0·01) for both acclimation periods, and an increasing, though non‐significant, trend between U _crit‐2 and temperature ( P  = 0·10). Acclimation temperature had no significant effect ( P  = 0·71) on the recovery ratio. These results indicate that a 48 h acclimation to experimental temperatures within the range of −3 to +8° C of the acclimation temperature may be sufficient in studies of swimming performance with this species. This ability to acclimate rapidly is probably adaptive for cutthroat trout and other species that occupy thermally variable environments.     

Age and growth of Anguilla anguilla in the Camargue lagoons

Age and total length ( L _T) data from a 11 year monitoring of the Anguilla anguilla eel population of the Camargue lagoons (Rhône delta, southern France) were collected for glass, yellow and silver eels. Three distinct models were calibrated to describe the growth process of undifferentiated eels, females and males, respectively. Uncertainty of parameter estimates was evaluated by bootstrapping. Females were characterized by larger asymptotic body size ( L _T) than males (580 ± 50 v . 388 ± 13 mm) and faster growth, whilst the Brody growth coefficient was larger for males than for females (means ±  s . d . 3·00 10⁻³ ± 1·68 10⁻³ v . 1·73 10⁻³ ± 0·50 10⁻³). Sexual differentiation was estimated to begin at 204 ± 38 mm mean ±  s . d ., i.e . at the end of the second year in the lagoons, well before the L _T at which macroscopic differentiation became possible ( c . 300 mm). Males probably leave the lagoon or die (due to either natural or fishing mortality) within the first 3 years, whilst females can remain up to 5 years. Sexual differentiation and maturation have a major role in shaping the L _T structure of the population. The L _T and mass ( M ) data were fitted by allometric curves     . The calibration of distinct curves for data from different years indicated that the allometric coefficient a was subject to wider interannual fluctuations than the allometric exponent b . A negative correlation linked the average L _T and the allometric exponent ( r  = −0·58, P  < 0·01).     

Changes in growth performance and proximate composition in Japanese flounder during metamorphosis

Morphological changes are described in Japanese flounder Paralichthys olivaceus larvae and juveniles with emphasis on growth during the period of metamorphosis. Ontogenetic changes in condition factor and lipid, glycogen and protein levels were also analysed to determine the utilization of stored energy. Fish grew from 6·6 to 20·3 mm L _T(1·15 to 84·4 mg in mass, M ) during the period from 11 to 40 days after hatching (DAH) at 19·3° C. Per cent specific growth rate per day (% G day⁻¹) for wet mass was lowest during the metamorphic phase (21–30 DAH) compared to pre‐(11–20 DAH) and post‐metamorphic (31–40 DAH) phases. When L _T and M were expressed as     , the b value was highest during the pre‐metamorphic phase and lowest during the metamorphic phase. These findings indicate that the developmental changes that occur during metamorphosis of Japanese flounder are closely related to the growth pattern. Moisture, lipid and glycogen contents were also at the lowest level during metamorphosis compared to pre‐ and post‐metamorphosis, which suggest that Japanese flounder use their energy reserves to accomplish metamorphosis due to an apparent decline in feeding during this period.     

A comparison of the maturation and growth of female flathead sole in the central Gulf of Alaska and south‐eastern Bering Sea

Female flathead sole Hippoglossoides elassodon maturity appears not to be area dependent since the total length ( L _T) at which 50% were mature ( L _T50) was similar for the central Gulf of Alaska (333 mm) and south‐eastern Bering Sea (320 mm) areas. Likewise the age at which 50% were mature ( A ₅₀) was similar in the south‐eastern Bering Sea (9·7 years) and central Gulf of Alaska (8·7 years). The timing of female flathead sole spawning may also be similar between areas. Batch or serial spawning was indicated for flathead sole. Female flathead sole grew at a similar rate in both the Gulf of Alaska and Bering Sea. In contrast, males grew faster in the Bering Sea than in the Gulf of Alaska. Males grew more slowly than females in both areas after 5 years of age, and reached a smaller maximum L _T. The growth of both sexes was similar during 1993 and 1996 in the Gulf of Alaska.     

Constraints of body size and swimming velocity on the ability of juvenile rainbow trout to endure periods without food

The hypothesis that body size and swimming velocity affect proximate body composition, wet mass and size‐selective mortality of fasted fish was evaluated using small (107 mm mean total length, L _T) and medium (168 mm mean L _T) juvenile rainbow trout Oncorhynchus mykiss that were sedentary or swimming ( c . 1 or 2 body length s⁻¹) and fasted for 147 days. The initial amount of energy reserves in the bodies of fish varied with L _T. Initially having less lipid mass and relatively higher mass‐specific metabolic rates caused small rainbow trout that were sedentary to die of starvation sooner and more frequently than medium‐length fish that were sedentary. Swimming at 2 body length s⁻¹ slightly increased the rate of lipid catabolism relative to 1 body length s⁻¹, but did not increase the occurrence of mortality among medium fish. Death from starvation occurred when fish had <3·2% lipid remaining in their bodies. Juvenile rainbow trout endured long periods without food, but their ability to resist death from starvation was limited by their length and initial lipid reserves.     

Temporal and spatial variation in potential and realized growth rates of age‐0 year northern rock sole

The possibility of prey limitations on the growth performance of age‐0 year northern rock sole Lepidopsetta polyxystra was evaluated at three sites along the north‐east coast of Kodiak Island, Alaska, U.S.A., by comparison of observed to potential growth rates. Growth potential was measured in the laboratory across the range of temperatures encountered by this species during the first summer of life. Growth potential ( g _L, mm day⁻¹) increased with water temperature (T) between 2 and 13° C, according to: g _L = 0·0151 + 0·3673·log₁₀(T). There were significant differences in growth rate between the three field sites such that Holiday Beach fish were 7·1 mm longer than Shakmanof Beach fish by mid‐September, with Pillar Creek Cove fish of intermediate size. Temperature differences between sites accounted for less than half of this variation. The remainder may have been related to differences in prey availability among the sites in association with observed differences in sediment characteristics. In addition to the spatial variability, there was significant monthly variation in growth performance. Realized growth rates between July and August were in excess of 85% of potential. Between August and September, however, realized growth fell to 43–71% of potential indicating a decline in conditions for growth. The spatial variation in growth rates was not density‐dependent as the site with the highest fish densities (Holiday Beach) also supported the highest growth rates. The available data indicates that for this subtidal species, interannual variation in growth may be more important than site variation.     

Growth variation in larval Makaira nigricans

The Atlantic blue marlin Makaira nigricans larvae were collected from Exuma Sound, Bahamas and the Straits of Florida over three summers (2000–2002). Sagittal otoliths were extracted and read under light microscopy to determine relationships between standard length ( L _S) and age for larvae from each year and location. Otolith growth trajectories were significantly different between locations: after the first 5–6 days of life, larvae from Exuma Sound grew significantly faster than larvae from the Straits of Florida. Exponential regression coefficients were similar among years for Exuma Sound larvae (mean instantaneous growth rate, G _L = 0·125), but differed between years for larvae from the Straits of Florida ( G _L = 0·086–0·089). Differences in larval growth rates between locations resulted in a 4–6 mm difference in L _S by day 15 of larval life. These differences in growth appeared to be unrelated to mean ambient water temperatures, and may have been caused by location‐specific differences in prey composition or availability. Alternatively, population‐specific differences in maternal condition may have contributed to these differences in early larval growth.     

Impact of temperature on food intake and growth in juvenile burbot

The effect of temperature on food consumption, food conversion and somatic growth was investigated with juvenile burbot Lota lota (age 0 years). Juvenile burbot showed a significant dome shaped relationship between relative daily food consumption ( C _R) and temperature ( T ) with C _R = − 0·00044 T ² + 0·01583 T  − 0·06010; ( n  = 90, r ² = 0·61). Maximum C _R was at 17·9° C (95% CL 17·2–18·6° C). The temperature related instantaneous growth rate ( G ) also followed a dome shaped function with G  = − 0·000063 T ² + 0·002010 T  − 0·007462; ( n  = 95, r ² = 0·57), with maximum growth rate at 16·0° C (95% CL 15·3–16·6° C). A significant linear relationship was found between the water temperature and the conversion coefficient ( C _C) with C _C = − 1·63 T  + 59·04; ( n  = 80, r ² = 0·74). The results indicate that juvenile burbot in large lakes benefit from higher water temperatures in the littoral zone, by increased food uptake and growth, especially during the warm summer months. Because profundal water temperatures do not reflect the optimal temperature for food consumption in large burbot, temperature is unlikely to be the main proximate factor for the obligate littoral‐profundal migration of juvenile burbot observed in many lake populations.     

Reproductive cycle and sex inversion in razor fish, a protogynous labrid in the southern Mediterranean Sea

The reproductive biology of the Mediterranean razor fish Xyrichthys novacula was investigated by demographic data and histological analysis of the female, intersexual and male gonads. Specimens were collected by bottom trawl on a monthly basis between June 2000 and July 2001 in a sandy bay in southern Thyrrenian. Gonad histology confirmed that the Mediterranean razor fish is a monandric, protogynous hermaphrodite. Females reached first sexual maturity at 100 mm ( L _T) and the estimated mean L _T at first maturity ( L ₅₀) was 125 mm. Females exhibited asynchronous ovarian development and multiple ovulations occurred over the spawning period. Vitellogenesis started in early May and spawning occurred from late May until late September. Sexual transition involved a large‐scale atresia of all oocyte stages and a massive degeneration of ovarian tissue followed by primordial germ cells proliferation. Sex change began at spawning time (June) but transitional individuals tended to cluster at the end of the reproductive period (September). They accounted for 17·1% of the population sampled and were found in a broad size range (105–150 mm L _T).     

Feeding ecology of silver hake larvae on the Western Bank, Scotian Shelf, and comparison with Atlantic Cod

The feeding ecology of the larvae of silver hake Merluccius bilinearis was examined during two time periods (October 1998 and December 1992) on the Western Bank, Scotian Shelf, north‐west Atlantic, and compared with the feeding ecology of Atlantic cod Gadus morhua larvae collected in the same samples in December 1992. During both time periods silver hake exhibited strong selection for late stage copepodids and adult copepods at a small size (>3·5 mm total length, L _T). The niche width measured as the diet breadth index ( I _DB) of silver hake declined rapidly as they increased in size and remained relatively constant from 3 to 11 mm L _T, during each time period. Atlantic cod larvae exhibited a broader niche width that was curvilinear over the same L _T. Atlantic cod were also less selective than silver hake, incorporating both naupliar and early stage copepodids in their diets throughout the length classes examined. Simple isometric relationships did not explain the differences in diet, as Atlantic cod larvae continued to feed on early stages of copepods at large size, while silver hake larvae quickly switched to large prey items. The strong selection and narrow I _DB observed for silver hake probably reflects adaptation to spawning during the periods between major secondary production peaks in temperate waters.