Development of the pectoral, pelvic, dorsal and anal fins in cultured sea bream

The pectoral fin girdle was the first element of the fins to develop in Sparus aurata. By 3·1mm L _N (notochord length) the cleithrum was ossified and the cartilaginous caracoid-scapula was present. The fin was fully developed at 11·6 mm L _S (standard length) and by 16·0 mm L _S most elements of the fin were ossified. The pelvic fins were the last pair to develop and rudiments of these were first detected at 7·9 mm L _S. The pelvic fin and girdle were completely formed and ossified at 16·0 mm L _S. The development of dorsal and anal fins began at c. 6·5–7·0 mm L _S with the formation of 10 cartilaginous dorsal proximal radials and eight cartilaginous ventral proximal radials. The three cartilaginous predorsals (supraneurals) appeared at 7·7 mm L _S and the ossification of dorsal and anal proximal and distal radials began, respectively, at 10·5 mm L _S and 11·3 mm L _S. Ossified structures in the fins were also classified according to their origin, as being either dermal or endochondral. Finally the chronology of appearance of fin structures in S. aurata was compared with that reported for other Sparidae, Engraulidae and Haemulidae.     

Shrinkage correction and length conversion equations for Theragra chalcogramma, Mallotus villosus and Thaleichthys pacificus

Preservation of walleye pollock Theragra chalcogramma, capelin Mallotus villosus and eulachon Thaleichthys pacificus by freezing decreased fork length ( L _F) up to 1·8, 5·6 and 2·7% and reduced mass by up to 8·4, 3·5 and 1·1%, respectively. Shrinkage of walleye pollock standard length ( L _S) was greater for fish in 95% ethanol v . 5% formalin and for fish in 10% formalin v . frozen. Equations describing the shrinkage and loss in mass for these species are presented as well as conversions between different length measurements ( L _S, L _F and total length, L _T) for fishes that were frozen.     

Larval development of five species of blenny (Teleostei: Blenniidae) from the western central North Atlantic, with a synopsis of blennioid family characters

Light trap collections on oil and gas platforms in the northern Gulf of Mexico off Louisiana from 1995 to 1997 contained young of tessellated blenny Hypsoblennius invemar , freckled blenny Hypsoblennius ionthas , featherduster blenny Hypleurochilus multifilis , molly miller Scartella cristata and seaweed blenny Parablennius marmoreus , which are described. Interspecific differences were: number of dorsal, anal, pelvic and caudal fin elements; number of mandibular pores; presence or absence of canine teeth, hypural 5 and pectoral fin pigment; width of gill openings; length of preopercular spines (in larvae). Size at settlement differed among some taxa, but all five species settled within a narrow size window of c . 1·5 mm standard length ( L _S). Hypsoblennius invemar , H. ionthas , H. multifilis and S. cristata settled at mean sizes between 11·3 and 12·1 mm L _S, whereas P. marmoreus settled at a mean size of 19·3 mm L _S. Sexually dimorphic differences were consistently evident by 17–18 mm L _S in all species but P. marmoreus . The two smallest blennies with external characters normally associated with sexual maturity were a 20 mm male and 21 mm female H. multifilis . Primary caudal fin rays began to bifurcate between 17·0 and 18·3 mm L _S in H. invemar , H. ionthas , H. multifilis and S. cristata . Hypleurochilus multifilis displayed the external characteristics of being sexually mature at 20–21 mm L _S. Thus, bifurcation of primary caudal fin rays was an indicator of approaching sexual maturity in H. multifilis and this may also be true in the other species studied.     

Ontogenic changes in the allometric scaling of the mass and length relationship in Sprattus sprattus

An analysis of mass ( M ) and standard length ( L _S) data for larval, juvenile and adult sprat ( Sprattus sprattus ; Clupeidae) revealed marked changes in the allometric scaling factor ( b in     ). For sprat <44 mm L _S, b was 5·0, whereas in larger juveniles and adults, b was c. 3·4 indicating a relatively protracted metamorphic period for this species.     

Kinematics of swimming of penguins at the Detroit Zoo

Kinematic parameters were examined in a study of the swimming abilities of seven species of penguins housed at the Detroit Zoo. Penguins produce thrust over both halves of the wing stroke cycle, as observed in fishes using the caudal or pectoral fins for locomotion, but not in other birds in level forward flight. Unpowered gliding phases between wing strokes were observed in all species at swimming speeds less than 1.25 m/sec, while Emperor, King and Adelie penguins interpose gliding phases over a broad range of speeds. Videotape records reveal that length-specific speed is correlated with increases in wingbeat frequency and, for most of the species examined, stride length. These findings are in contrast to those reported for other, flying birds, which maintain a relatively constant wingbeat frequency but vary stride length with forward speed, and for most fishes, which vary speed with tailbeat frequency but maintain a constant stride length. The results are somewhat comparable to those reported for Cymatogaster , a fish which uses the pectoral fins for locomotion. Drag coefficients of three gliding Emperor penguins were 2.1, 3.0 and 3.0 × 10-⁻³ at Reynolds numbers of 1.25, 1.62 and 1.76 × 10⁶, respectively.     

Reproductive costs to male and female worm pipefish

Prior to reproductive maturity male and female worm pipefish Nerophis lumbriciformis are not significantly different in standard length ( L _S), eviscerated mass or condition indices. Subsequently, however, mature females achieve significantly ( P  < 0·001) greater values of L _S and mass. For egg-bearing males, there was no marked difference in the mass of embryos with increasing development ( P  > 0·1); similarly there was no significant divergence in condition indices calculated for males carrying embryos of increasing development. Post-brooding males, however, had significantly lower values for the hepato-somatic index than either egg-bearing or non-mated male worm pipefish ( P  < 0·001). This study suggests that male worm pipefish invest a significant proportion of their energy budget into the development and maintenance of the brooding patch, to the detriment of increased length or mass.     

Larval development of Argentine hake Merluccius hubbsi

The ontogeny of the developmental stages of the hake Merluccius hubbsi is described. Fish larvae and post-transitional juveniles were collected in the Nor-Patagonian area from 1989 to 2004. The opening of the mouth and the pigmentation of the eyes are coincident with yolk resorption, finishing the yolk-sac stage. This species presents pigmentation on the head, trunk and tail typical of gadiform larvae. Pectoral fin development is completed during the transformation stage. The post-transitional juvenile stage begins when the fin-ray complements are complete and squamation begins. The fins become fully formed in the following sequence: pelvic fins, first dorsal fin, second dorsal and anal fins together, caudal fin and pectoral fins. The caudal complex is totally developed in larvae of 22·0–23·0 mm standard lengths ( L _S) and all vertebral elements are first observed in larvae of 8·5 mm L _S. The rate of development of M. hubbsi observed in this study could be faster than the rates reported for other species of Merluccius by different authors.     

Morphological development and allometric growth patterns in the juvenile seahorse Hippocampus kuda Bleeker

The morphological development and allometric growth patterns in the juvenile spotted seahorse Hippocampus kuda were studied under hatchery rearing conditions. Newborn spotted seahorses [mean ± s.d . standard length ( L _S) 9·33 ± 0·79 mm] were raised till the age of 124 days (119·35 ± 6·04 mm). Growth was characterized by three stages with two inflexion points occurring at day 21 and 76. The mean growth rates in the first, second and third stages were 0·68, 1·16 and 0·71 mm day⁻¹, respectively. The growth rate was most rapid in the second stage and was probably influenced by a behavioural shift from pelagic to benthic form. The mass ( M ) and L _S relationship was exponential ( M = 7·14 × 10⁻⁶ L _S^2·76), but the slope, b = 2·76, reflected negative allometric growth. Sexes could be distinguished at c. 110 days, and the sex ratio was unbiased. The L _S in males and females did not differ significantly. Morphological stageing series is proposed, which divides H. kuda juvenile development into eight stages based on the development of coronet, cheek and eye spines, keel and pigmentation. The morphometric ratios for all the body parts, except trunk length, showed considerable changes at a transition point occurring at c. 25 mm L _S. The high proportional growth in head length, head depth, pectoral fin base length, dorsal fin base length, snout length, snout depth and eye diameter at the initial stages, and the abrupt increase in tail length only after the first 2 weeks, possibly reflect development priorities during early development where important organs are being developed first for the enhancement of juvenile survival.     

Response to conspecific and heterospecific alarm cues by pumpkinseeds in simple and complex habitats: field verification of an ontogenetic shift

Three focal size classes [small (<40 mm, standard length, L _S), medium (40–80 mm L _S) and large (>80 mm L _S)] of pumpkinseed Lepomis gibbosus were exposed to conspecific or one of three heterospecific chemical alarm cues under one of three levels of habitat complexity (low, intermediate and high). Under low and intermediate habitat complexities, pumpkinseeds <80 mm L _S exhibited a significant antipredator response when exposed to the chemical alarm cues of heterospecific prey guild members (largemouth bass Micropterus salmonides and hypoxanthine‐3‐ N ‐oxide, the putative Ostariophysan alarm 'pheromone'), while pumpkinseeds >80 mm L _S exhibited a foraging response. Under highly complex habitats, pumpkinseeds of all three size classes exhibited an antipredator response. Moreover, under all three habitat conditions, pumpkinseeds of all size classes exhibited an antipredator response to conspecific alarm cues. There was no change in behaviour under any treatment combination in response to an allopatric heterospecific control (swordtails Xiphophorus helleri ). These results provide the first field verification of the size dependent use of chemical alarm cues by centrarchids and demonstrate that microhabitat complexity significantly influences the threat‐sensitive use of these cues.     

Larval Konosirus punctatus(Clupeidae) in a brackish river mouth on the Pacific coast of central Japan

Eggs of Konosirus punctatus in early developmental stages were collected from the eastern part of the mouth of Sagami Bay on the Pacific coast of central Japan. Advanced‐stage eggs and early larvae with notochord length ( L _N) of <7·5 mm were collected from the inner bay near the mouth of the Sagami River. Feeding larvae of >8·4 mm L _N were distributed in the mouth of the river, and juveniles of 24–90 mm standard length ( L _S) were collected from the lower reaches of the river between the river mouth and c . 3 km upstream of the river mouth. Hatch dates of larvae and juveniles collected in 2001 ( n  = 158) and in 2002 ( n  = 109) extended from late March to late July. The relationship between the otolith radius ( R _O) and L _N or L _S changed during the metamorphosis stage as characterized by 320 μm R _O and 22 mm L _S. Otolith growth rate, as an index of somatic growth rates in larval and early juvenile stages, was higher in cohorts that hatched later in the spawning season, i.e . from March to July. Konosirus punctatus that were spawned in the bay mouth area survived with different growth histories in the bay and lower reaches of the river, and recruited to the young‐of‐year population in the Pacific coastal waters of central Japan.     

Seasonal, diel and ontogenetic variation in feeding patterns of small yellow croaker in the central Yellow Sea

Stomach contents of 1603 small yellow croaker Pseudosciaena polyactis , sampled from seasonal bottom trawl surveys in the central Yellow Sea between March 2001 and January 2002, were examined. The results showed that small yellow croaker was a carnivorous predator and >30 prey species were identified from stomach contents analysis. Crustaceans (mainly euphausiids and decapods) were the most important prey, occurring in 93·1% of the stomachs containing food, and accounting for 77·6% of the total food by mass. Feeding activity was highest in autumn and lowest in spring and winter. Decapods were more important in summer, whereas euphausiids were more important during other seasons. Ontogenetic differences were found in the diet composition and feeding activity within the range of size (standard length, L _S) studied. The importance of fishes and decapods increased with L _S, whereas euphausiids, copepods and amphipods decreased in importance with L _S. Dietary breadth increased markedly for adults. A positive relationship was found between L _S and prey size. In each season the maximum diel feeding activity occurred at 0800 and 2400 hours, indicating that there was crepuscular and nocturnal feeding by small yellow croaker.     

A new technique to gather 3‐D spatial information using a single camera

A new technique using a single camera and shadows to determine 3‐D spatial positions of fishes in the laboratory is described. The apparatus consisted of a large aquarium (2·0 × 1·5 × 0·4 m), a wide‐angle camera mounted above and two light sources to cast shadows to either side of the fish. Using image analysis and vector mathematics, aquarium objects were plotted within 1·5 cm of their actual location along the x ‐, y ‐ and z ‐axis. The technique was also successful in quantifying changes in 3‐D spatial pattern of juvenile fish, Atlantic cod Gadus morhua (7·4–8·6 cm standard length, L _S) and cohabitant piscivorous shorthorned sculpin Myoxocephalus scorpinus (12·0–25·8 cm L _S), at these same viewing fields. The new technique should have a wide application, largely because it is potentially less expensive, laborious and invasive than alternative methods for determining 3‐D positions of fishes.     

Development of osteological structures in the sea bream: vertebral column and caudal fin complex

The development of cartilaginous structures in cultured sea bream Sparus aurata larvae and the timing of their ossification was studied. In cultivated sea bream larvae the first cartilaginous structure to be identified was hypural 1 at 4.1 mm notochord length ( L _N). By 5.3 mm L _N, prior to the onset of ossification, it was possible to distinguish the following cartilaginous structures: all 23 neural arches, all 13 haemal arches and two of the four pairs of parapophyses. The neural arches 1–4 and 15–23 were formed on the notochord and elongated dorsally, while neural arches 5–14 appeared on the dorsal side of the spinal cord and elongated ventrally. Initiation of ossification occurred at 5.7–6.0 mm standard length ( L _S) when the cartilaginous ontogeny of the vertebral column was completed. Ossification was coincident with dorsal flexion at the posterior end of the notochord and occurred in a sequential manner: (1) dorsoanteriorly, the cartilaginous neural arches and the centra were the first structures to ossify; (2) ventrad at the centre, at 7.0–7.5 mm L _S; (3) posteriorly at 7.1 mm L _S the hypural complex and urostyle (24th centrum) were ossified; and (4) dorsad at the centre (neural arches and spines).     

Consumption and gut evacuation rate of laboratory‐reared spotted seatrout (Sciaenidae) larvae and juveniles

The temperature and mass dependence of maximum consumption rate was measured for larval and early juvenile spotted seatrout Cynoscion nebulosus . Maximum consumption ( C _MAX) estimates were obtained from feeding and gut evacuation experiments on larvae (3·8–19 mm standard length, L _S) at three temperatures (24, 28 and 32° C), and maximum consumption experiments on juveniles at three temperatures (20, 26 and 32° C). Feeding levels were determined for larvae fed live prey ( Brachionus plicatilis and Artemia salina ) ad libitum . The midgut and total evacuation times were estimated for fish feeding continuously and discontinuously using alternate meals of tagged and untagged live prey. Temperature and fish size had significant effects on gut evacuation and consumption. The gut evacuation time increased with increasing fish size, and decreased with increasing temperatures. Mass‐specific midgut contents increased for small larvae <0·156 mg dry mass ( M _D)( c . 4 mm L _S), and decreased for larger larvae and juveniles. Maximum consumption was modelled by fitting a polynomial function to a reduced dataset of individuals feeding at high levels. The C _MAX model predicted an initial increase in specific feeding rate from 70 to 155% M _D day⁻¹ for small larvae, before declining for larger larvae and juveniles.     

Gait transition speed, pectoral fin-beat frequency and amplitude in Cymatogaster aggregata, Embiotoca lateralis and Damalichthys vacca

Surfperches are labriform swimmers and swim primarily with their pectoral fins, using the tail to assist only at higher speeds. The transition, from pectoral to pectoral and caudal fins, occurs at a threshold speed that has been termed physiologically and biomechanically 'equivalent' for fishes of different size. The gait transition ( U _P-C) of Cymatogaster aggregata occurred at a higher speed (measured in bodylengths s⁻¹) for smaller fish than larger fish. At U _P-C, pectoral fin-beat frequency was size-dependent: smaller fish have a higher pectoral fin-beat frequency than larger fish. In contrast, at low speeds (i.e. <60% of U _P-C) the pectoral fin-beat frequency was independent of the size of the fish. Inter-specific comparisons of U _P-C, pectoral fin-beat frequency and amplitude among C. aggregata, Embiotoca lateralis and Damalichthys vacca showed that C. aggregata had a higher U _P-C than E. lateralis and D. vacca . The pectoral fin-beat frequency at U _P-C showed no significant differences among species. Cymatogaster aggregata achieved higher U _P-C, in part, through increased fin beat amplitude rather than frequency. These differences in performance may be related to the different habitats in which these species live.     

The feeding ecology of Morone americana larvae in the Chesapeake Bay estuarine turbidity maximum: the influence of physical conditions and prey concentrations

Feeding ecology of white perch Morone americana larvae, a major component of the ichthyoplankton community in the estuarine turbidity maximum (ETM) region of upper Chesapeake Bay, was evaluated in years of contrasting physical conditions. In 1998, high river flow led to an ETM with high turbidity and pronounced salinity stratification. In 1999, under low river flow conditions, turbidities in the ETM region were lower and the salt front was located 15 km up‐stream of its location in 1998. Copepodites and adults of Eurytemora affinis were the predominant prey in guts of all length classes of larvae (3·2–9·8 mm standard length, L _S) that were examined. Repeated‐measures, multiple regression analyses were conducted to evaluate the influence of several factors on feeding success by determining if physical conditions (temperature, current velocity, salinity, turbidity and light) and prey concentrations explained variability in mean gut fullness (gut contents mass per body mass) of small (<5 mm L _S) and large (>5 mm L _S) white perch larvae. Eurytemora affinis concentrations were significant in the statistical models for both small and large larvae. High concentrations of E. affinis , which enhanced encounter rates of white perch larvae with prey, may have been the most important factor determining feeding success in the ETM region. Larval feeding incidence (percentage of guts with food) was higher in 1998, suggesting that annual variability in river flow influenced larval feeding success by controlling physical and biological conditions in the ETM region.     

Fish habitat associations in a spatially variable desert stream

White sands pupfish Cyprinodon tularosa were sampled with minnow traps along the length of Lost River, a highly variable desert stream in New Mexico, to evaluate if their abundance, median standard length ( L _S) and sex ratio values differed by microhabitat variables. Habitat measurements were made in a 4 m² area around the minnow trap. White Sands pupfish populations were primarily structured by L _S. As specific conductance and surface area increased, median size of fish decreased. Shallow areas with higher specific conductance were correlated with an increased number of fish.     

Growth of North Alboran Sea sardine larvae estimated by otolith microstructure, nucleic acids and protein content

Wet mass and DNA, RNA and protein content increased significantly with standard length ( L _S) of sardine Sardina pilchardus larvae, collected in January 1995, in the Bay of Málaga, North Alboran Sea. L _S, wet mass and DNA, RNA and protein content were closely related allometrically to otolith radius ( R ). Larval daily length increments decreased but DNA, protein and wet mass daily increments increased with larval age. Daily length increments showed a negative and poor relationship with long-term otolith growth. In contrast, DNA, protein and wet mass daily increments were positively correlated. Differences between observed and back-calculated otolith radius-at-age indicated that larvae with slow otolith growth were under represented in older age groups, suggesting the existence of growth-selective mortality. Recent otolith growth, estimated from the mean widths of the last six increments, increased with age and R . Individual RNA: DNA and protein: DNA ratios were correlated significantly, although weakly, with L _S and larval growth.     

Gape morphology of cod Gadus morhua L., haddock Melanogrammus aeglefinus (L.) and whiting Merlangius merlangus (L.) through metamorphosis from larvae to juveniles in the western Irish Sea

Variations in standard length ( L _S), gape size ( S _G) and jaw length ( L _J) were studied in larval and juvenile gadoids (cod Gadus morhua , haddock Melanogrammus aeglefinus and whiting Merlangius merlangus ) from 4 to 70 mm. The increase in S _G and L _J was not linear with respect to L _S. The relationship was best described by segmented regression lines in all three species, with an inflection point at c . 10·5 mm. The S _G and L _J increased more rapidly in relation to larval L _S for individuals smaller than this inflection point size. The rates of increase slowed significantly post-inflection, an effect more noticeable in S _G data compared to L _J data. In each case, the inflection point fell in the intermediate period of development between the larval and juvenile stages, which could be considered as metamorphosis. Published equations that have been used to predict S _G from L _J lead to the overestimation of gape. New relationships are presented, which may be used to predict S _G from measurements of either L _S or upper jaw length in cod, haddock and whiting.     

Effect of body size, temperature, and salinity on the routine metabolism of larval and juvenile spotted seatrout

Routine oxygen consumption rates of young spotted seatrout Cynoscion nebulosus (Sciaenidae) were measured over a range of temperatures (24, 28, 30 and 32° C) and salinities (5, 10, 20, 35 and 45). Larvae and juveniles, 4·1–39·5 mm standard length ( L _S), ranging several orders of magnitude in dry body mass were used to estimate the mass–metabolism relationship. Oxygen consumption (μl O₂ larva⁻¹ h⁻¹) scaled isometrically with body mass for larvae <5·8 mm L _S(phase I, slope = 1·04) and allometrically thereafter (phase II, slope = 0·78). The inflection in the mass–metabolism relationship coincided with the formation of the hypural plate and an increase in the relative tail size of larvae. Salinity did not have a significant effect on routine metabolism during phase I. Temperature and salinity significantly affected routine metabolism during phase II of the mass–metabolism relationship. The effect of salinity was temperature dependent, and was significant only at 30° C. Response surfaces describing the environmental influences on routine metabolism were developed to provide a bioenergetic basis for modelling environmental constraints on growth.