Feeding, morphological changes and allometric growth during starvation in miiuy croaker larvae

We investigated the effects of the timing of first feeding (larvae in F0, F1, F2, F3 and S were first fed on day 3, 4, 5, 6 days after hatching (DAH) and unfed, respectively) on feeding, morphological changes, survival and growth in miiuy croaker larvae at 24°C. The fed larvae initiated feeding on 3 DAH and reached point of no return (PNR) on 6 DAH. Larvae in F0 and F1 groups survived apparently better than F2 group at the end of the experiment on 36 DAH. High larval mortality occurred from 3 to 7 DAH in all feeding groups, accounting for 40% (F0, F1 and F2 groups) to 90% (F3 and S groups) of the total mortality. Larvae in F0 and F1 groups grew better than F2 group throughout the experiment. Eye diameter, body height, head height and mouth gape of the first feeding larvae were more sensitive to starvation than other morphometrics and could be used as indicators for evaluating their nutritional status. Results indicated that delayed first feeding over 1 day after yolk exhaustion could lead to poor larval survival and growth. To avoid starvation and obtain good growth in culturing, larvae feeding should be initiated within 1 day after yolk exhaustion at 24°C.     

First feeding and subsequent growth performances in piscivorous larvae of Chinese perch Siniperca chuatsi (Perciforms: Sinipercidae)

The success of first feeding is influenced by many factors, such as prey availability, and is critical to subsequent larval growth performances. To test the advantages of prey exposure before complete yolk absorption in piscivorous larvae, feeding incidence and specific growth rate were longitudinally measured in Chinese perch Siniperca chuatsi larvae first fed at different ages. The results showed that Chinese perch larvae were able to capture live piscine prey at 4 DAH (days after hatching), 1 day before complete yolk absorption. The feeding incidence and specific growth rate were higher in larvae first fed at 4 DAH than in larvae first fed at 5 or 6 DAH. These results indicate that prey exposure experience can facilitate the onset of first feeding, and that successful exogenous feeding, even before complete yolk absorption, is important for growth performances of piscivorous fish larvae.     

Feeding behaviour of Japanese flounder larvae under laboratory conditions

Tank–reared Japanese flounder larvae, Paralichthys olivaceus , had a major feeding peak in the morning and a secondary peak in the afternoon throughout the larval development, with light being the primary factor regulating their feeding activity. The larvae consumed rotifers in preference to Artemia for up to 10 days, after which the food preference shifted to Artemia . Feeding rates of the larvae prior to 10 days post–hatch depended on prey density, but in the old larvae, feeding rates were independent of prey density. Maximum feeding rate occurred at 19° C. The occurrence of the attack posture, after its onset at first feeding (2 days post–hatch), increased up to 25 days, began to decrease when the larvae prepared to settle down, then disappeared after settlement. The occurrence frequency of the attack posture was positively related to fish density, but inversely related to starvation duration, and occurred most frequently at 19° C. This posture depended on prey density in larvae prior to 10 days post–hatch, but became independent of prey density as the larvae developed. It was obvious that, for flounder larvae, attack posture was a behavioural character closely related to feeding and subject to larval development and environmental factors.     

Effects of temperature and delayed initial feeding on the survival and growth of Japanese flounder larvae

The effects of the timing of initial feeding (0, 1, 2, 3 and 4 days after yolk exhaustion) and temperature (15, 18 and 21° C) on the point‐of‐no‐return (PNR), survival and growth of laboratory‐reared Japanese flounder Paralichthys olivaceus larvae were studied under controlled conditions. The larvae reached PNR on 7·7, 5·2 and 4·2 days‐post‐hatching (dph) at 15, 18 and 21° C, respectively. At each temperature, larval growth did not differ significantly among the delayed initial feedings 1 day before PNR but decreased significantly in larvae first fed after that. In the treatments where initial feeding was equally delayed, larvae grew significantly faster at 18 and 21° C than at 15° C. The larvae survived apparently better at 15 and 18° C than at 21° C when initial feeding was equally delayed. At each temperature, survival of the larvae first fed before PNR did not differ noticeably, while delayed initial feeding after that apparently reduced their survival. These results indicated that there existed a negatively temperature‐dependent PNR in the Japanese flounder larvae. Survival and growth of the larvae strongly depended on temperature as well as the timing of initial feeding. High temperature accelerated the yolk exhaustion and growth of the larvae and thus reduced their starvation tolerance and survival. To avoid potential starvation mortality and obtain good growth, the Japanese flounder larvae must establish successful initial feeding within 2 days after yolk exhaustion at 15° C and within 1 day at both 18 and 21° C.     

Effects of the timing of initial feeding on growth and survival of spotted mandarin fish Siniperca scherzeri larvae

The effects of delayed first feeding on growth and survival of spotted mandarin fish Siniperca scherzeri larvae were examined under controlled conditions. Morphometric characters [yolk‐sac volume, oil globule volume, head depth (H_D), body depth (B_D), eye diameter (E_D), musculature height (M_H), mouth diameter (M_D) and total length (L_T)], body mass (M), specific growth rate (S_GR) and survival were evaluated under different first‐feeding time (2, 3, 4 and 5 days after hatching). Larvae began to feed exogenously at 2 days after hatching (DAH) and the point of no return (P_NR) occurred between 5 and 6 DAH at 23° C, range ±1·0° C. The yolk volume of larvae first‐fed at 2 days had a significant difference compared with that of larvae first‐fed at 3, 4 and 5 days on 3 and 4 DAH. The larvae first‐fed at 2 days achieved comparatively better growth performance than that of 3, 4 and 5 days. On 5 DAH, all morphometric characters had significant differences between 2 and 5 days and 2 and 4 days initial feeding, respectively. Total mortality was recorded on 9 DAH for the larvae first‐fed at 5 days. On 12 DAH, significant differences were observed between 2 and 4 days and 3 and 4 days initial feeding for all morphometric characters. From 16 DAH to the end of experiment, all growth variables of the larvae first‐fed at 2 days were significantly higher than those in other treatments. The S_GR (2–9 DAH) first‐fed at 2 and 3 days were significantly higher than 4 and 5 day treatments, and the S_GR (9–16 DAH) first‐fed at 2 days was significantly higher than 3 and 4 day treatments. There was no significant difference, however, of S_GR (16–28 DAH) among treatments. Survival rate was significantly higher at 2 days initial feeding (27·42%) when compared with 3 (15·96%) and 4 days (7·92%) initial feeding at the end of experiment. The present study suggests that the first feeding of S. scherzeri larvae should be initiated at 2 days after hatching for achieving good growth and survival.     

Density-dependent predation and implications for stock enhancement with Japanese flounder

In laboratory predation trials kinsen-gani crab Matuta lunaris rarely preyed on hatchery-reared (HR) Japanese flounder Paralichthys olivaceus , even at extremely elevated prey densities ( c . 90 fish m⁻²), but fed readily on sacrificed Japanese founder. This suggests that under similar conditions in the wild predator-prey interactions between kinsen-gani and juvenile Japanese flounder are likely to be weak. Larger Japanese flounder readily cannibalized smaller conspecifics, suggesting that within-release group cannibalism may contribute considerably to post-release mortality of HR Japanese flounder when sufficient size variation exists within groups of released fish. Kinsen-gani presence had no effect on within-release group cannibalism rates of large Japanese flounder on small Japanese flounder. Within-release group cannibalism rates were significantly affected by densities of smaller (prey) fish, implying that the number of fish released (and thus post-release densities) in stock enhancement programmes may significantly affect post-release mortality rates. The probability of within-release group cannibalism increased rapidly as the cannibal-to-prey size ratio exceeded 1.6, suggesting that minimizing size variation of released HR individuals will reduce post-release cannibalism rates. These results have implications for Japanese flounder stock enhancement release strategies, and may be applicable to other finfish stock enhancement programmes.     

Developmental change in RNA: DNA ratios of fed and starved laboratory-reared Japanese flounder larvae and juveniles, and its application to assessment of nutritional condition for wild fish

Starved Japanese flounder Paralichthys olivaceus larvae were characterized by relatively lower levels of RNA content throughout their early life stages. Significant differences in the RNA: DNA ratios were found between fed and starved fish, and appeared to increase as starvation proceeded. Ontogenetic changes in RNA: DNA ratios were clearly observed during metamorphosis, especially decreasing during the period from the late-metamorphic to postmetamorphic stages. The criteria established from these laboratory experiments, were applied to the nutritional condition of wild larvae and juveniles collected in Wakasa Bay, Sea of Japan in 1994 and 1995 by measuring RNA and DNA content. Starved fish were mainly found in stage I (settling stage) fish during the late season of settlement in 1995. This suggests that starvation could be associated with settlement in Japanese flounder.     

Assessment of the nutritional status of field-caught larval Pacific bluefin tuna by RNA/DNA ratio based on a starvation experiment of hatchery-reared fish

RNA/DNA ratio is a useful and reliable indicator of the nutritional status of fish larvae and juveniles. In order to assess the nutritional status of field-caught larval Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel), starvation experiments of hatchery-reared larvae were conducted and changes in the RNA/DNA ratio of fed and starved larvae were analyzed. Starvation experiments were conducted every 3 days after first feeding. The survival rate of Pacific bluefin tuna larvae ranged 10-50% after 1 day of starved conditions and growth retardation was observed immediately. These results suggest that Pacific bluefin tuna larvae have a very low tolerance to starvation. The RNA/DNA ratios of fed larvae were approximately 2.0-4.0. On the other hand, the value of starved larvae significantly decreased to 1.0-3.0. The nutritional status of 3 cohorts of field-caught tuna larvae collected in the northwestern Pacific Ocean was examined based on the value of the RNA/DNA ratio of the 1 day starved larvae. 4.35-25.77% of the cohorts were regarded as the “starving condition”, which was negatively correlated to the ambient prey densities. These findings suggest that the nutritional condition of larval Pacific bluefin tuna was influenced by the ambient prey density, and starvation itself and starvation-induced predation could greatly contribute to mortality in the larval period of Pacific bluefin tuna.     

Effects of starvation on morphometric characteristics of olive flounder, <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>

An experiment was conducted for 12 weeks to determine the effect of feeding and starvation on truss and classical parameters in the external body of olive flounder, Paralichthys olivaceus. There was an increase in the truss dimension of body depth in the trunk region of the fed group at the end of the experiment (P < 0.05). In the olive flounder, the trunk region dimensions, including body depth measurements, are likely to be compromised by variability related to differences in the feeding of fish from different habitats. Classical dimensions in relation to the anterior–posterior body axis decreased and classical dimensions of head characteristics increased upon starvation but decreased upon feeding (P < 0.05). These results suggest that these morphometric parameters may be a useful index of nutritional status in olive flounder.     

Feeding ability and survival during starvation of marine fish larvae reared in the laboratory

The larvae of Clyde and Baltic herring (Clupea harengus L.), cod (Gadus morhua L.) and flounder (Platichthys flesus L.) were reared and fed to examine the changes in feeding ability and survival during progressive starvation. The time to initial feeding for yolk-sac larvae and to the point-of-no-return (PNR, when 50% of the larvae, although still alive, are no longer strong enough to feed) for both yolk-sac and older larvae were determined. The yolk-sac larvae of Clyde and Baltic herring, cod and flounder begin to feed on days 6, 3, 5 and 6 post-hatching at rearing temperatures of 7.5, 9.2, 6.9 and 9.5°C, respectively. The time to reach the PNR for yolk-sac larvae of these species is only 3–5 days after yolk resorption. From the onset of starvation in older larvae the time to reach the PNR is 6–7 days for 36-and 60-day-old Clyde herring at 9.6 and 10.5°C and for 46-day-old Baltic herring at 13.1°C but it is 23 days for 32-day-old flounder at 12.3°C. In yolk-sac larvae the peak of feeding rate and intensity usually occurred on the day that the yolk became exhausted, or 1 day later. Older larvae could withstand longer periods without food than yolk-sac larvae, especially in flounder. While the feeding rate during starvation of older larvae slowly decreased the feeding intensity first increased significantly and then decreased. Survival of larvae remained high up to the PNR.     

Diet composition,feed preferences and mouth morphology of early stage silver therapon (Leiopotherapon plumbeus,Kner 1864) larvae reared in outdoor tanks

This study examined the diet composition, feeding preferences, and mouth morphology of the silver therapon (Leiopotherapon plumbeus, Kner 1864) larvae under captive conditions. Larvae were reared in outdoor tanks (4 m³) with natural food grown 2 weeks prior to start of larval rearing. Food preference was measured by the Chesson's electivity index (α_i). Gut content analysis of larvae sampled between 5 and 25 days after hatching (DAH) showed the dominance in the diet by zooplankton, mainly copepod nauplii, cladocerans and insect larvae. Small fish larvae (5–9 DAH; 3.32–6.29 mm standard length) preferred cladocerans, ciliates and copepod nauplii; whereas older larvae (12–25 DAH; 5.45–19.26 mm standard length) preferred insect larvae over cladocerans and adult insects. The mouth gape size at 5 DAH was 359 μm and increased to 3.75 mm at 40 DAH when body size grew at an average rate of 0.59 mm d^?1. The standard length (SL) of L. plumbeus larvae was strongly associated with mouth size (r² = 0.98, P < 0.05), indicating a progressive increase of ingested prey size of the fish larvae. These results clarified the early life feeding ecology of this species, which is essential in developing effective hatchery techniques.     

Morphophysiological studies on alligator gar (Atractosteus spatula) larval development as a basis for their culture and repopulation of their natural habitats

Natural populations of alligator gar (Atractosteus spatula) have declined recentlydue to the effects of commercial and sportfisheries. Aquaculture represents a short-termalternative to restore natural populations, anda first step to accomplish culture of thisspecies is the study of early life stages.Therefore, multidisciplinary research was usedto describe the major morpho-physiologicalchanges taking place during this period. Thestudies serve as a basis for the introductionof artificial diets for culture. Amorphological study distinguished differentnutritional stages, as well as externalindicators of starvation. A histologicalapproach showed the digestive tract to becompletely formed 5 days after hatching (DAH),at the beginning of exogenous feeding.Throughout larval development, intestinalmaturation was followed and a nutritionalindicator based on the mid-gut cell height wasvalidated. The occurrence of pepsin-likeproteolytic activity was detected from fiveDAH, while trypsin, chimiotrypsin andaminopeptidase-like activities graduallyincreased from two to nine DAH. The incidenceof cannibalism in culture conditions wascontrolled by exposure to anti-thyroidcompounds (thiourea – TU) to retard snoutgrowth. This treatment did not effect growthand allowed juveniles to feed on live prey butprevented the consumption of gar larvae of thesame size. Larvae exposed to3,3,5-triiodo-1-thyronine (T3) had fasterdevelopment, a potentially advantageouscharacteristic for the repopulation of theirnatural habitat. Finally, artificial feeds werewell accepted and resulted in growth ratessimilar to those of gar larvae that were fednatural prey. This has allowed the developmentof a feeding strategy that effectively reducedcannibalism and led to the production of 30 cmjuveniles in four months.     

Effect of delayed first feeding on development and feeding ability of Paralabrax maculatofasciatus larvae

The impact of delayed feeding early in development on late feeding ability and development of spotted sand bass Paralabrax maculatofasciatus larvae was examined. Larvae were sampled from hatching until day 19 after delayed feeding for zero (control), 1, 2, or 3 days. Feeding incidence was evaluated as the percentage of larvae with food in the gut and feeding intensity was measured by direct counting of prey after dissection of the gut. Delayed feeding effects due to starvation were observed early in development. By day 5, significant differences ( P  < 0·05) were observed between controls and larvae submitted to degrees of delayed feeding, including total length ( L _T), eye diameter, and the size of the head, liver, gut, muscles and body. Differences were still apparent in L _T, and body, liver and muscle heights at the end of the studied period. Larvae under total starvation did not survive beyond day 5. Initial feeding incidence was 35, 60, 90 and 10% for larvae first fed on day 2, 3, 4 or 5, respectively. Mean ±  s . d . feeding intensity was 3·6 ± 0·8, 2·8 ± 1·3, 5·2 ± 0·3, and 10·2 ± 1·5 rotifers per larva depending on whether larvae were initially fed on day 2, 3, 4 or 5, respectively. The point of no return occurred between 4 and 5 days after hatching.     

Growth and nutritional condition of the larvae of Odontesthes microlepidotus (Atherinidae): an experimental approach

Synopsis The relation between the feeding and mortality of fish larvae is mediated not only by starvation but also by their growth. In this work, daily otolith ring deposition was analysed in laboratory-reared larvae of Odontesthes microlepidotus (Jenyns), and their growth was studied in relation to ring number and otolith diameter. The nutritional condition of these larvae was assessed by means of morphometric comparisons between fed and starved larvae in order to develop a tool to evaluate the nutritional status of larvae in breeding areas. Changes in body shape have been found as a consequence of starvation. No dependence was found between mean hepatocyte nuclear area and fasting.     

微颗粒饲料与冰冻桡足类对大黄鱼稚鱼生长、存活和体成分的影响(英文)

评估三种新开发的微颗粒饲料(Diet 1,Diet 2和Diet 3)、一种混合饲料(Diet 4:Diet 3和冰冻桡足类混合投喂)和冰冻桡足类(Diet 5)对25–60日龄大黄鱼稚鱼的饲喂效果。Diet 1组大黄鱼稚鱼的特定生长率(SGR,7.97%/d)和成活率(40.0%)最高,而Diet 5组稚鱼的SGR(4.15%/d)和成活率(20.4%)最低。Diet 4组稚鱼的成活率与Diet 1组差异不显著,但其SGR低于后者。从稚鱼的SGR和成活率看,三种微颗粒饲料中,Diet 1要优于Diet 2和Diet 3。各处理组中每桶稚鱼的生物量与SGR有相似的变化趋势。各微颗粒饲料组稚鱼的体蛋白含量差异不显著,低于Diet 4组,但高于Diet 5组。而微颗粒饲料组稚鱼的脂肪含量(10.6%–13.3%)均显著高于Diet 4组(7.6%)和Diet 5组(7.2%)。尽管冷冻桡足类中C20:4n–6(AA)的含量稍低于微颗粒饲料,但Diet 4和Diet 5组稚鱼的AA含量均显著高于微颗粒饲料组。Diet 4和Diet 5组稚鱼的C22:6n–3(DHA)分别高于其相应饲料中的含量。相反地,微颗粒饲料组稚鱼的C20:5n–3(EPA)低于微颗粒饲料中的含量。这些结果表明,Diet 4和Diet 5组稚鱼体内AA、DHA和EPA的沉积效率高于微颗粒饲料组。研究表明,大黄鱼稚鱼可用微颗粒饲料"断奶"。基于Diet 1优于Diet 2和Diet 3,可将其作为进一步研究的基础配方。此外,有必要对各处理组大黄鱼稚鱼消化酶和消化道的变化进行研究以综合评估微颗粒饲料的效果。     

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.     

Cholecystokinin (CCK) in Atlantic herring (Clupea harengus L.) - ontogeny and effects of feeding and diurnal rhythms

Neural and alimentary cholecystokinin (CCK) levels in Atlantic herring, Clupea harengus, were analyzed from hatching to 40days after hatching (DAH). The head compartment representing the neural pool was quantitatively dominant (>80% of the total CCK content) while the digestive tract pool represented 6-10%. During ontogeny the CCK level in whole larvae increased almost 15-fold from 0 to 40 DAH, being particularly marked from 14 to 20 DAH. Larvae of 24 to 26 DAH were examined for potential occurrence of a circadian rhythm and to analyze the effects of feeding. Fed and fasted larvae were significantly different, where fed larvae showed higher CCK levels. There were large fluctuations in CCK levels analyzed at 3h intervals without an apparent diurnal pattern. Shorter sampling intervals of 1h in the morning when lights were switched gradually on and food was offered to the larvae demonstrated a marked drop in the relative gut CCK levels and a concurrent increase in the CCK carcass to gut ratio, 1h after introduction of food followed by a return to prefeeding levels after 2h. This response probably results from a release and re-synthesis of CCK in the gut after initiation of feeding. Taken together, these results support earlier reports that CCK participates in the regulation of digestive processes in herring larvae, but CCK does not seem to have a circadian rhythm independent of feeding.     

EVALUATION OF MICRODIETS VERSUS FROZEN COPEPODSON GROWTH, SURVIVAL AND SELECTED CHEMICALCOMPOSITION OF LARGE YELLOW CROAKERPSEUDOSCIAENA CROCEA LARVAE

Three newly developed microdiets (MDs: Diet 1, Diet 2 and Diet 3), one co–feeding diet (Diet 4, combinedDiet 3 with frozen copepods) and frozen copepods (Diet 5) were tested for weaning large yellow croaker (Pseudosciaenacrocea) larvae from 25 to 60 days after hatching (DAH). The highest final specific growth rate (SGR, 7.97%/d) and sur-vival (40.0%) were observed in fish fed Diet 1, while those were the lowest in fish fed Diet 5 (4.15%/d and 20.4%, re-spectively). The survival of larvae fed Diet 4 showed no significant difference (P>0.05) from that of larvae fed Diet 1.However, SGR of larvae fed Diet 4 was significantly lower (P<0.05) than that of larvae fed Diet 1. Among the MDs,Diet 1 was proved to be superior to Diet 2 and Diet 3 for both SGR and survival. For all treatments, biomass in each tankwas observed a similar trend as SGR. Whole-body protein was not significantly different (P>0.05) among fish fed theMDs, which was lower than that of fish fed Diet 4, but higher than that of fish fed Diet 5. Fish fed the MDs had signifi-cantly higher (P<0.05) lipid deposition (10.6%—13.3%) than fish fed either Diet 4 (7.6%) or Diet 5 (7.2%). DietaryC20:4n-6 (AA) level was significantly lower (P<0.05) in Diet 5 than that in the MDs. However, the AA level was sig-nificantly higher (P<0.05) in fish fed either Diet 4 or Diet 5 than that in fish fed the MDs. The exceeded C22:6n-3 (DHA)levels in fish compared to their corresponding diets were found in those fed either Diet 4 or Diet 5. Inversely, C20:5n-3(EPA) and DHA levels decreased in fish fed the MDs relative to their proportions in MDs. These results showed that fishfed either Diet 4 or Diet 5 had higher efficiency of AA, DHA and EPA deposition than fish fed the MDs. This study sug-gested that large yellow croaker larvae could be successfully weaned by MD. Future research should be based on for-mula of Diet 1, since it was superior to Diet 2 and Diet 3. In addition, changes of digestive enzymes and digestive tractof large yellow croaker larvae fed different diets need to be investigated for an overall evaluation.     

Trypsin activity and physiological aspects in larval rearing of European sea bass (Dicentrarchus labrax) using live prey and compound diets

The aim of this study was to evaluate the potential of a compound diet as a live prey substitute for feeding European sea bass larvae ( Dicentrarchus labrax L.). The effect of a commercial diet (Nippai ML feed) and live prey ( Artemia nauplii) on tryptic enzyme activity, protein content, growth (standard length) and survival rates of sea bass larvae were tested during a 27-day rearing experiment. Sea bass larvae were divided into two groups. The live food group (control group) was fed exclusively on newly hatched Artemia nauplii (Inve AF grade), the test group was fed exclusively with the compound diet from day 15 onwards. As trypsin has been demonstrated to be a useful indicator for evaluating digestibility of food and the nutritional condition of fish larvae, individual tryptic enzyme activity was determined in both feeding groups. Larvae older than 14 days after hatching and fed on live food showed a significantly higher tryptic enzyme activity than larvae fed the compound diet. A similar relationship between tryptic activity and standard length in both test groups was detected only in small larvae (standard length < 7 mm). The usefulness of proteolytic enzyme activity measurements in larval fish research, as well as its use in aquaculture nutrition research, was confirmed. Protein content, increase in length and survival rates of the sea bass larvae were additionally determined in order to evaluate an influence on the diet. The protein content of larvae fed the Artemia nauplii was higher and the growth of larvae fed the compound diet was reduced. Larval mortality was not affected by the diet given.     

The effects of predation on the survival and size-distribution of estuarine fishes: an experimental approach

Synopsis The effect of southern flounder,Paralichthys lethostigma, predation on the survival and size-distribution of spot,Leiostomus xanthurus, was investigated using feeding experiments in outdoor tanks and estuarine ponds. In the outdoor tank experiments, southern flounder, 143 mm average standard length (SL), fed for 48 h on spot (25–30 mm SL), over a range of densities (4–20 m^–2). In these trials, flounder showed a Type II functional response to spot density. In the estuarine pond experiment, flounder density (2 or 4 flounders 70 m^–2) contributed significantly to spot mortality relative to predator-free controls. The effect of flounder density on spot mortality was non-linear; in the 4-flounder treatment the daily instantaneous mortality due to flounder (0.0177) was 3.5 times that in the 2-flounder treatment (0.0051). The total spot mortality rate in the 4-flounder treatment (0.028) was similar to that observed from published field observations. Flounder also altered the size distribution of spot relative to predator-free controls. Predation by flounder resulted in fewer intermediate-sized spot at the end of the experiment when compared to predator-free controls. Flounder also significantly reduced survival and mean length of two killifishes,Cyprinodon variegatus andFundulus heteroclitus, that invaded the pond. Flounder predation was a significant size-structuring force on the prey fish assemblage in the pond. Results from both the outdoor tank experiment and the pond experiment indicate that flounder may represent a significant source of mortality for juvenile estuarine fishes.