Episodes of starvation are recorded in the otoliths of juvenile Ambassis vachelli (Chandidae), a tropical estuarine fish

Juvenile Ambassis vachelli, 40 to 50 d old, were used to test the effects of starvation and recovery-feeding on the widths of otolith increments. Three laboratory treatments (fed continuously; fed for 9d then starved for 15 d; starved for 9 d then fed for 15 d), were compared. Fish were also collected throughout the experiment from a field site to assess the natural fluctuations of increment widths. Growth, starvation and recovery were reflected in the widths of otolith increments. The width of increments deposited during starvation were similar in all fish, regardless of prior feeding history, despite the lower mortality recorded in starved fish with a history of intense feeding. Increment-width data were confounded by an ontogenetic decrease in increment widths with age. The results indicate that starvation and recovery are recorded in the increment widths of otoliths and are distinguishable from the effects of ontogenetic development. However, ontogenetic changes in the width of otolith increments confounded the interpretation of otolith-increment series. Therefore, the ontogenetic pattern of otolith increments must be known for each species before valid interpretation of otolith microstructure is possible.     

Otolith record of age, growth, and ontogeny in larval and pelagic juvenile Stephanolepishispidus (Pisces: Monacanthidae)

Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S. hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed that increment formation was not significantly different than one increment per day, and thus, increment number was used to estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain, South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition. All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40% conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population level, but unresolved at the individual level. Received: 1 November 1999 / Accepted: 18 December 2000     

Life history and fishery of Lepidopus caudatus (Pisces: Trichiuridae) in the Catalan Sea (Northwestern Mediterranean)

The frostfish Lepidopus caudatus (Euphrasen, 1788) is a mesopelagic species; it occurs along the shelf and slope down to 450 m in the Catalan Sea. Its' fishery, population structure, growth, diet and reproduction was studied on the basis of commercial statistics from 1984 to 1990 and on samplings made in 1988 and 1989. L. caudatus is fished by two types of commercial method, trawl and long-line; catches by the latter method display a marked seasonality. The minimum size of fish caught is 26 cm total length by trawling and 71 cm by long-line. Maximum sizes are similar for both gears: 196 and 188 cm, respectively. L. caudatus exhibits fast growth and attains an age of 8 yr. It feeds on small mesopelagic prey. It is a partial spawner reproductive activity occurring from April to November. Males attain sexual maturity at 97 cm and females at 111 cm total length.     

Validation of daily increment deposition in otoliths. Age and growth determination of Aphia minuta (Pisces: Gobiidae) from the northwest Mediterranean

The transparent goby Aphia minuta (Risso, 1810) is one of the main target species of the small-scale fishery off the Island of Majorca. Otolith microstructure and length-frequency analysis were used to study the age and growth of this species during the 1982/1983 and 1992/1993 fishing seasons. Daily periodicity of increment formation was determined by experiments with marked otoliths in individuals maintained in captivity. The length range of the catches during the 11 yr period was between 12 and 49 mm, with a main distribution (89%) between 24 and 40 mm. Otolith age-readings indicate that the population exploited in the commercial fishery consists of seven age-groups (2 to 8 mo old), with a very high proportion of individuals (95%) between 3 and 6 mo old. Population growth-curves revealed no differences between males and females. The growth parameters for the whole population are: asymptotic length, L _∞ = 53.69 mm; growth coefficient, K = 2.23 yr⁻¹; theoretical age at length zero, t ₀ = −0.005 yr. Those individuals of A. minuta caught in Majorca during the winter period reached a maximum age of 7 or 8 mo. Received: 30 December 1996 / Accepted: 16 April 1997     

Effects of feeding history on the growth characteristics of a reef fish at settlement

A feeding experiment was conducted on the pelagic stages of the tropical goatfish Upeneus tragula (family Mullidae) to examine how food quantity affects growth characteristics and potential success at settlement. Pelagic goatfish were collected from aggregation rafts 3 nautical miles west of Lizard Island on the northern Great Barrier Reef during December 1990. Three tanks in each of four feeding regimes were stocked with 25 pelagic goatfish between 20 and 23 mm standard length (SL). The four feeding regimes were: fed ad lib. (fed): fed once per day (f1pd); starved every second day (stld); starved for 3 d and re-fed (st3d). Fishes were fed 36 to 48 h old Artemia sp. nauplii (Ocean Star strain). Fish were removed from tanks when they underwent metamorphosis, changed pigmentation and settled to the bottom of the tanks. Morphology, muscle development, time taken to settle and biochemical condition were examined. Growth attributes of the treated fish were compared to fish which settled within 24 h of capture (field). All attributes examined were significantly influenced by the feeding treatments. Fish within the fed and st3d treatments were significantly larger and heavier than fish in the less well-fed treatments (f1pd, st1d). Similarly, concentrations of total lipid, carbohydrate and protein in the settled fish were significantly higher in the fed and st3d treatments compared with the st1d and f1pd treatments. For all these morphological and biochemical attributes the st1d and f1pd fish did not significantly differ from the field fishes, but did differ from the fed and st3d fishes. Water content was significantly higher in the f1pd, st1d and field fishes compared with the fed and st3d fish. Furthermore, the average time taken to settle followed the pattern: fed (14d)U. tragula are physiologically well suited to exploiting a patchy food source, and that food availability within the pelagic stages can have a major influence on the growth characteristics of this reef fish at settlement. The ramifications of this finding are discussed in relation to survival and success once fish have recruited to the reef population.     

Morphological and functional development of larval and juvenile Limanda yokohamae (Pisces: Pleuronectidae) reared in the laboratory

Morphological and behavioural aspects in larval development need to be studied in detail to understand the early life history better, and to gain a comprehensive knowledge on early life stages for fish species important in aquaculture and fisheries. In the present study, larvae of Limanda yokohamae (Günther) were reared to observe their behavioural development, and to obtain specimens for studying the morphological features and the intestinal development at Ohno, Hiroshima, Japan, in 1987. Swimming activity was monitored at several larval stages, and swimming speed was recorded until settlement and after-feeding behaviour was initiated. A slight increment of swimming speed was observed with larval growth. Larvae changed their swimming behaviour from surface waters to the bottom of the rearing tank when their eyes began to move. Morphological development of pigmentation patterns, fin development, squamation and the development of the digestive tract were described and illustrated in detail to characterize development stages, especially those relating to metamorphosis. During metamorphosis, growth ceased and rapid changes in allometric growth were accompanied by differentiation of the digestive tract. After metamorphosis there was steady growth, allometric growth achieved a constant value, and both the scales and digestive organs were fully formed. Metamorphosis was therefore a crucial developmental milestone, including a critical phase during which survival potential was lowered.     

Suitability of estuarine nursery zones for juvenile weakfish (Cynoscion regalis): effects of temperature and salinity on feeding,growth and survival

Juvenile weakfish, Cynoscion regalis (Bloch and Schneider, 1801), exhibit significant spatial diffrences in growth rate and condition factor among estuarine nursery zones in Delaware Bay. The potential influence of temperature and salinity on the suitability of estuarine nursery areas for juvenile weakfish was investigated in laboratory experiments by measuring ad libitum feeding rate, growth rate and gross growth efficiency of juveniles collected in Delaware Bay in 1990 (40 to 50 mm standard length; 1.4 to 2.1 g) in 12 temperature/salinity treatments (temperatures: 20, 24, 28°C; salinities: 5, 12, 19, 26 ppt) representing conditions encountered in different estuarine zones during spring/summer. Feeding rates (FR) increased significantly with temperature at all salinities, ranging from 10 to 15% body wt d^-1 at 20°C to 33–39% body wt d^-1 at 28°C. Specific growth rates (SGR) ranged from 1.4 to 9.4% body wt d^-1 (0.3 to 1.5 mm d^-1) and gross growth efficiencies (K ₁) varied from 13.6 to 26.4% across temperature/salinity combinations. Based on nonlinear multiple regression models, predicted optimal temperatures for SGR and K ₁ were 29 and 27°C, respectively. Salinity effects on SGR and K ₁ were significant at 24 and 28°C where predicted optimal salinity was 20 ppt. At these warmer temperatures, SGR and K ₁ were significantly lower at 5 than at 19 ppt despite higher FR at 5 ppt. Therefore, maximum growth rate and growth efficiency occurred under conditions characteristic of mesohaline nurseries. This finding is consistent with spatial patterns of growth in Delaware Bay, implying that physicochemical gradients influence the value of particular estuarine zones as nurseries for juvenile weakfish by affecting the energetics of feeding and growth. Laboratory results indicate a seasonal shift in the location of physiologically optimal nurseries within estuaries. During late spring/early summer, warmer temperatures in oligohaline areas permit higher feeding rate and faster growth compared to mesohaline areas. By mid-late summer, spatial temperature gradients diminish and mesohaline areas provide more suitable physicochemical conditions for growth rate and growth efficiency whereas oligohaline areas become energetically stressful. Substantial mortality occurred at 5 ppt and 28°C, providing additional evidence that oligohaline conditions are stressful during late summer. Furthermore, juveniles provided a choice among salinities in laboratory trials preferred those salinities which promoted higher growth rates. The extensive use of oligohaline nurseries by juvenile weakfish despite the potential for reduced growth rate and growth efficiency suggests this estuarine zone may provide a substantial refuge from predation.     

Effects of temperature on oxygen consumption,growth, and development of embryos and yolk-sac larvae of Siganus randalli (Pisces: Siganidae)

Eggs from laboratory spawnings of the coralreef fish Siganus randalli Woodland were incubated at two temperatures (27 and 30 °C). Eggs and larvae were sampled until larval starvation, while changes in oxygen consumption, growth, yolk utilization, and development were monitored. Oxygen consumption, which peaked at hatching, was higher for embryos incubated at 30 °C than at 27 °C. Rates of oxygen consumption (nl h^-1 individual^-1) at hatching were similar to those for other temperate and tropical species. Rates of oxygen consumption by yolk-sac larvae were highly variable, and these data suggest that larval oxygen consumption prior to yolk-sac absorption may not be significantly influenced by temperature. Rates of yolk depletion were higher for larvae at the higher temperature. After an initial rapid increase in length, length of larvae at 30 °C decreased with age. Egg size, egg weight, and maximum notochord length of larvae differed significantly between spawns. Age-specific oxygen consumption rates by the embryos varied between spawns, but regressions describing oxygen consumption as a function of age did not differ significantly. The initiation and completion of eye pigmentation were used as developmental markers to calculate the amount of yolk remaining for larvae at the different temperatures. Larvae maintained at 30 °C completed eye pigmentation approximately 3 h sooner than those maintained at 27 °C, but had less endogenous reserves. This finding indicates a trade-off between rapid development and efficient utilization of the endogenous reserves. The completion of eye pigmentation in larvae incubated at the higher temperature occurred at midnight and, depending on the amount of time that the larvae have to initiate feeding prior to the point-of-no-return, the timing of completion of eye pigmentation could influence larval survival.     

Comparisons of the feeding activity and diets of male and female cunners Tautogolabrus adspersus (Pisces: Labridae)

The diel distribution of feeding activity during the spawning season was compared for territorial male and female cunners Tautogolabrus adspersus in Conception Bay, Newfoundland, Canada between June and August, 1978. Territorial males feed significantly less often than females and concentrate their feeding activities in the morning, whereas females feed as frequently in the afternoon as in the morning. Based on the contents of alimentary tracts, territorial males, non-territorial males, and females have different diets. Since these three groups share the same habitat, the observed dietary differences probably reflect differences in their foraging behaviour. The relevance of these findings to the concept of time minimizer and energy maximizer is discussed.     

Assessment of the nutritional condition of larval and early juvenile tuna and Spanish mackerel (Pisces: Scombridae) in the Panamá Bight

The nutritional condition of first-feeding and late larval/early juvenile scombrids was investigated in waters of the northwestern Panamá Bight from May through early November 1988. Wild-caught larvae and juveniles of three taxa, black skipjack tuna (Euthynnus lineatus), bullet and/or frigate tuna (Auxis spp.) and sierra (Scomberomorus sierra), were examined histologically to determine nutritional condition. The incidence of malnourishment in wild-caught preflexion (first feeding—prior to notochord flexion) larvae of all taxa was high. Starvation rates for E. lineatus and Auxis spp. preflexion larvae ranged from 62 to 63% d^-1, while the percentage of larvae actually dying of starvation was estimated at 41 to 43% d^-1. The nutritional point-of-no-return for preflexion larvae was estimated at 1 to 2 d maximum. The cellular condition of liver hepatocytes, particularly the relative amount of vacuolation related to storage of glycogen and lipid, proved to be a sensitive indicator of nutritional condition. In laboratory trials, late larval (postflexion) and early juvenile black skipjack exhibited a nutritional point-of-no-return of 2 to 3 d. Although postflexion larvae were moderately vulnerable to malnourishment in laboratory trials, <13% of wild-caught postflexion larvae exhibited even mild nutritional stress, and no postflexion larvae or juveniles showed signs of severe malnourishment. This pattern of starvation incidence suggests that tropical scombrids undergo stagespecific starvation mortality. Preflexion larvae can suffer significant daily losses due to starvation, while postflexion larvae and early juveniles seem to experience a rapid improvement in feeding ability and/or food availability.     

Risk of predation and the feeding behavior of juvenile coho salmon (Oncorhynchus kisutch)

Summary During their first 1–2 years of life, juvenile coho salmon (Oncorhynchus kisutch) are stream-dwelling, and feed upon drifting invertebrates. They move upstream from a holding position to intercept individual prey items; the distance moved (attack distance) is an increasing, but decelerating, function of prey size. Since the fish are presumably more visible to predators during such feeding excursions, prey size and risk are associated variables.The effect on attack distance of the presentation of a model predator (a photograph of a rainbow trout) was examined in the laboratory. Attack distances are shortened following presentation of a predator; this is particularly true when the prey are large (Fig. 1). The extent of the reduction of attack distance is directly related to predator presentation frequency, although there appears to be a minimum level to which it will decline (Fig. 2). Hungry fish and fish in the presence of a competitor (simulated by a mirror) are less responsive to the predator, suggesting a trade-off of energetic requirements and risk (Fig. 3 and Table 3). The effect of predation risk should be to reduce the relative proportion of large prey in a juvenile coho's diet, and its net rate of energy intake.     

Effects of temporary starvation on the survival,and on subsequent feeding and growth,of oyster (Crassostrea gigas) larvae

Larvae of oysters, Crassostrea gigas, were maintained without food for 1 to 8 d after fertilization, and fed daily thereafter. There was little difference in survival and growth between controls and larvae kept without food for 2 or 3 d. Survival and growth rates were depressed in larvae starved for 4 or 5 d. For larvae starved for 6 to 8 d, survival was negligible or nil; even those larvae which survived the starvation period died later in the presence of food, apparently because of impaired digestion. Therefore, food availability in the first few days after spawning appears to be of paramount importance to the successful recruitment of Pacific oysters.     

The effect of temperature-salinity combinations on survival and growth of juvenile Patiriella pseudoexigua (Echinodermata: Asteroidea)

Adult Patiriella pseudoexigua were collected in October 1989 from Wanlitung, Taiwan and then induced to spawn in the laboratory. Post-metamorphosed juvenile P. pseudoexigua were reared on a diet of benthic algae Navicula sp. at 25°C and salinity (34). Six weeks after metamorphosis, juvenile P. pseudoexigua at ca. 400 m in radius were reared on a diet of benthic algae Navicula sp. at different combinations of temperatures (20, 25, 30°C) and salinities (26, 30, 34) for 40 d. Both temperature and salinity had a significant effect on juvenile survival and growth. Juveniles survived best (>90%) at 25°C and 34 and grew best (to ca. 750 m in radius) at 30°C and 34. Variation in juvenile size was small immediately after metamorphosis and increased with time.     

Haemocyanin concentration of juvenile lobsters (Homarus gammarus) in relation to moulting cycle and feeding conditions

Groups of laboratory-reared, juvenile lobsters (Homarus gammarus, 40–50 g wet weight) were given different types of food (shrimp, mixed invertebrates and pellets, bivalves, starved) for a period of 22 wk. Haemocyanin concentration was measured weekly, moult stage and moultings noted. Haemocyanin concentration decreased rapidly in the starved group (from 0.8–0.6 to 0.2 mM). The group fed with bivalves showed a small decline with time, to 0.5–0.3 mM at the end of the period, indicating a deficient diet. The haemocyanin in the other groups did not change significantly during the experiment. Moultings decreased in frequency and the intermoult period was prolonged when the quality of food was decreased, and in the starved group moulting ceased completely after 1.5 months. Haemocyanin concentration was lowest immediately after moult and increased gradually through stages C and D. Lobsters that were starved or maintained on the bivalve diet did not reach the same premoult haemocyanin levels as those fed with shrimps and mixed food.     

Eggs and early larvae of Thrissocles species (Engraulidae: Pisces)

Eggs of Thrissocles species are found in surface plankton in the Ernakulam Channel (Cochin Harbour)during February to May 1967. The eggs hatch within 24 h. Empty egg shells have characteristic apertures, through which the embryos have emerged; yolk is resorbed 36 h after hatching.Larvae (36 to 72 h groups) assemble at the lighted region of the aquaria during day-time and scatter to different levels at night. Larvae older than 72 h show no inclination to assemble as before. All larvae died between 96 and 110 h after hatching. Many batches of eggs were reared in the same medium, and all of them behaved as described. The results indicate that the right type of food was available in the aquaria for larvae up to a period of 72 h. The volume of water also appears to have a bearing upon the survival rate and longevity of the larvae since, in small aquaria, more larvae died at an early stage.     

Karyotypes in two species of the genusHippocampus (Pisces: Syngnatiformes)

Diploid modal numbers of chromosomes 2n=48 forHippocampus ramulosus and 2n=44 forH. hippocampus, collected in the Gulf of Palermo in May 1985, are established. No sex-linked heteromorphic pairs are observed in the two species analyzed. The karyotype ofH. hippocampus seems to be a derived condition.     

Effects of current speed on filtration during suspension feeding in Oligometra serripinna (Echinodermata: Crinoidea)

Suspension feeding by the crinod Oligometra serripinna was studied at Lizard Island, Australia, in 1986. Video recordings were made of 90-m particles interacting with the filter of the crinoid in a laboratory flow chamber. A complete census of particles was possible because both the capture event and the filter area could be defined unequivocally. Also, because O. serripinna is a passive suspension feeder, a census of partcles could be made at different ambient current speeds without interference due to active pumping by the crinoid. Experiments were run at seven current speeds from 0.9 to 13.3 cm s^-1. Particles approaching the filter: (1) were captured, (2) passed through the filter without triggering a capture event, (3) passed through the filter after escaping from an unsuccessful capture event, or (4) were deflected around the filter. With increasing current speed, the proportion of deflections declined and the proportion of particles passing through rose: these results could be partially explained by the progressive widening of the spaces within the filter due to distortion of filter parts by the current. The proportion of captures (normalized to approaches) was comparatively low at 0.9 cm s^-1, rose to a relatively constant maximum from 1.7 to 6.4 cm s^-1, and then declined progressively at 9.5 and 13.3 cm s^-1. These proportions were translated into capture rates for whole crinoids by taking into consideration both the encounters with particles and the reduction of filter area by distortion of body parts at higher speeds. When plotted against current speed, capture rate peaked at 6.4 cm s^-1, which was close to the mean current speed that we measured on the reef in the microhabitat of O. serripinna.