Compensatory growth responses in juvenile fat snook,Centropomus parallelus Poey,following food deprivation

The compensatory growth in juvenile fat snook (13.7 g) was evaluated in fish subjected to four treatments: continuously fed (control); subjected to 1 (D1), 2 (D2) and 3 (D3) weeks of food deprivation, followed by a 5‐week re‐feeding period. At the end of food deprivation, the body weights at the different treatments were significantly different and inversely related to the length of the food deprivation period (C=16.425 g; D1=14.024 g; D2=13.542 g; D3=12.228 g). During re‐feeding, no differences were observed in the slopes of body weight growth curves among treatments, indicating failure in full growth compensation. In the first re‐feeding week (week 4), although hyperphagia was observed for all re‐fed groups, better food conversion ratios were detected only for D1 and D2, reflected in an enhancement in the specific growth rates. From week 5 onwards, no differences between treatments and control were detected for any variable. The total food intake was lower for D2 and D3 compared with the control. In the present study, fish showed partial compensatory growth when subjected to a maximum of 2 weeks of food deprivation. Therefore, the food deprivation can promote production losses, even considering a reduction in the total food intake.     

Economies of scale for juvenile production of common snook (Centropomus undecimalis Bloch)

Abstract

Construction and operating costs for three common snook (Centropomus undecimalis) hatcheries in Florida, USA, are illustrated. Hypothetical capacities and targets of the three hatcheries (Scenarios I, II and III respectively) were 615, 000 juveniles (8 ‐ 10 g in weight) for stock enhancement, and 1, 275, 000 and 3, 000, 000 juveniles (1‐g in weight) for commercial grow‐out. Estimated production costs were lower than for many marine finfish species. The 20‐year mean costs per 1, 000 juveniles were estimated to be $324, $215, and $159, for hatcheries I, II, and III respectively, and the initial capital investments were $731, 660, $1, 162, 460, and $1, 896, 030¹, respectively. Major cost items of annual production were labor (22 ‐ 33%), supplies (14 ‐ 20%), fixed costs (15 ‐ 17%), and interest (13 ‐ 15%). The most profitable hatchery was the 3 million 1‐g juvenile hatchery due to the hatchery size effect, with a net present value (NPV) of $1, 760, 000, an internal rate of return (ERR) of 81%, a payback period of 3.6 years, and a profitability index of $2.86 for every dollar invested. Possible cost reductions to increase financial profitability were discussed.     

再次分级、驯食对小规格鳡生长、残食的影响

研究了再次分级、驯食对初次分级产生的鳡(Elopichthys bambusa)幼鱼弱小群体(S群)生长、存活的影响。试验设5组,A组试验鱼取自初次分级并驯食后的大规格群(B群),为对照组;B、C、D、E组取自S群,B组再次分级不再驯食,所分两级为B1、B2亚组;C组再次分级再次驯食,两级为C1、C2亚组;D组不再分级再次驯食;E组不再分级不再驯食。饲养85 d。结果显示:A组全长(TL)、体重(BW)始终最高,终末BW以E组最低;E组体重特定生长率(SGRBW)(55～139 DAH)最低;总存活率(SR)(55～139 DAH)A组最高,C组其次,E组最低;总残食率(CR)(55～139 DAH)E组最高,D组其次;初始体重变异系数(CVBW)对总CR影响显著(P=0.001),可用线性模型y=0.514 9x-7.761 7(r2=0.667)阐释两者关系。结果表明,再次分级和再次驯食有利于S群存活,但不能使S群规格在85 d内追及B群。     

Effects of stocking density on growth and survival of young Gulf killifish in recirculating aquaculture systems

Gulf killifish, Fundulus grandis, is a hardy marine baitfish with established rearing techniques in ponds and static pools, but there is little information about the use of recirculating aquaculture systems (RAS) for growing killifish.The current trial investigated the effects of stocking density on growth and survival of young killifish in RAS. Young fish (28-day posthatch) of 51.6 ± 0.9 mg (mean ± SE) were stocked at 2, 5, 8, and 11 fish/L in 31 L tanks in RAS with triplicate groups for 16 weeks. Cannibalism was a major problem in the study, which increased with increasing initial stocking density, affecting survival negatively. Survival decreased (P < 0.03) with increasing initial stocking density and culture period. At the end of the trial, the 2, 5, 8 and 11 fish/L initial stocking density reduced to 1.66, 1.42, 0.86, and 0.74 fish/L respectively. A significant linear relationship existed between the initial stocking density and weight (y = 0.077x + 2.3; R² = 0.8; P = 0.003), whereas an inverse relationship occurred between initial stocking density and survival parameters (y = ?9.43x + 97.4; R² = 0.89; P < 0.001). From the trial, the optimum density for culturing young of Gulf killifish in RAS appears to be around two fish/L.     

Influence of temperature on yolk resorption in common snook Centropomus undecimalis (Bloch, 1792) larvae

To determine the optimal rearing temperature for Centropomus undecimalis larvae during the yolk resorption period, changes in larval development were measured at four different temperatures (23, 25, 28 and 31°C). Yolk and oil‐globule volume was recorded for 25 larvae at four different times. This involved an initial measurement at hatch and at 24, 48 and 72 h posthatch (hph). Additional morphological measurements included standard length, body height and eye diameter. On average, at the end of the three trials, larvae reared at 25°C had a longer mean standard length than larvae reared at 23, 28 and 31°C. Larvae reared at 25°C also had more yolk and oil globule reserves than larvae raised at 28 and 31°C. The body height:length residuals were also the highest at 25°C (i.e. larvae had deeper or stockier bodies). The yolk sac was present up to 72 hph at 23 and 25°C, while it was entirely consumed after 48 hph in larvae held at 28 and 31°C. Larvae showed the fastest growth during the first 24 hph in all temperature treatments; this period corresponded to the highest energy consumption as determined by the decrease in yolk sac and oil‐globule volume. Eye diameter did not vary significantly with time during yolk‐resorption. We conclude that a temperature near 25°C is optimal for raising snook larvae during the yolk‐resorption period.     

Effects of stocking density on the survival, growth, size variation and condition index of juvenile rabbitfish Siganus rivulatus

Spinefoot rabbitfish, Siganus rivulatus, is an economically important species of herbivorous fish that is relatively easy to rear and thus considered to be suitable for aquaculture. Juveniles are generally reared in nursery systems before being stocked into growout cages or ponds. We report here our evaluation of the effects of stocking density on the survival, growth, feed efficiency and condition index of S. rivulatus juveniles in nursery tanks. The experiment was conducted in a recirculating system of twelve 52-l aquaria connected to a biological filter and a sand filter. Juvenile fish (average weight 6.5 g) were stocked into aquaria at four stocking densities (10, 20, 30, and 40 fish/aquarium) with three replicate aquaria per treatment. Diet was provided at 3% body weight daily divided into two feedings. Fish were weighed weekly for 8 weeks and the diet increased accordingly. Survival was greater than 95% in all treatments, with no significant differences observed among treatments. There were also no differences in specific growth rate (SGR 2.12–2.27) of the fish among treatments. Growth rate was linear during the 8 weeks in all treatments, and harvested biomass increased proportionally to stocking density (198, 401, 600 and 785 g per increasing stocking density, respectively). Feed efficiency (FE 0.67–0.71) of the fish did not vary significantly among treatments. The coefficient of variation was high (35–41%) among the harvested fish, but it also did not differ significantly among treatments. The final condition indices of the fish in all treatments were similar to each other but significantly greater than the initial values (P < 0.05). The results suggest that there is no apparent effect of stocking density at the levels tested on the survival and growth of juvenile rabbitfish.     

Effects of the initial size, stocking density and sorting on the growth of juvenile Pacific abalone, Haliotis discus hannai Ino

During winter months, a novel overwintering mode of transferring juvenile abalones to open seawaters in southern China rather than keeping them in closed land-based nursery systems in northern China is a popular practice. The initial size, stocking density and sorting are among the first considerations when establishing an abalone culture system. This study aimed to investigate the effects of these factors on the growth of juvenile Pacific abalone, Haliotis discus hannai Ino, during overwintering. Juvenile abalones were reared in multi-tier basket form for overwintering in open seawaters in southern China for 106 days. The daily growth rates (DGRs) in the shell length of all experimental groups ranged from 67.08 to 135.75 μm day⁻¹, while the specific growth rates (SGRs) were 0.2447–0.3259% day⁻¹. Variance analysis indicated that both DGRs and SGRs in shell length were significantly affected by the initial body size and stocking density. Furthermore, the effects of stocking density on DGRs and SGRs varied with the initial size. However, sorting abalones according to their initial sizes may not be necessary in practice as sorting did not alter growth significantly at all densities in this study. Factors potentially affecting abalone growth such as genetic control and intraspecific competition were discussed.     

Effects of stocking density on mortality,growth and physiology of juvenile Amur sturgeon (Acipenser schrenckii)

To evaluate effects of stocking density on welfare of Amur sturgeon (Acipenser schrenckii), an experiment was designed using three initial stocking densities in flow‐through tanks (LSD = 3.7 kg m^?3, MSD = 6.9 kg m^?3, and HSD = 9.3 kg m^?3, respectively) for 60 days. Growth, body composition, and haematological and biochemical parameters were monitored. The mortality and feed conversion rate (FCR) were not affected by stocking density. However, the specific growth rate (SGR), final weight and weight gain in the HSD group were significantly lower than in the LSD and MSD groups. The hepatosomatic (HSI) and viscerosomatic indices (VSI) varied inversely with regard to stocking density. Stocking density did not affect crude protein levels in fish. In contrast, the total lipid level was significantly higher in the LSD group compared to the MSD and HSD groups. The levels of erythrocytes and haemoglobin were positively correlated with stocking density. Serum total bilirubin and urea in HSD group were significantly higher than in the LSD group while serum triglycerides showed opposite tendencies. Differences between treatments were not registered for glucose, total protein and albumin. In conclusion, higher stocking density resulted in increased immunosuppression and enhanced energy mobilization. The latter was necessary to enable Amur sturgeon to cope with crowding.     

密度胁迫对凡纳滨对虾稚虾免疫指标及生长的影响

将体长为（3.59±0.26）cm的凡纳滨对虾（Litopenaeus vannamei）按1 800尾.m-3、1 500尾.m-3和1 200尾.m-3的密度分别饲养在注水0.3 m3的圆形玻璃纤维桶（容量为0.5 m3）中30 d,检测了基本水质因子、对虾肝胰腺和肌肉组织中的酚氧化酶（PO）活力、超氧化物歧化酶（SOD）活力、抗菌活力（Ua）、碱性磷酸酶（AKP）活力、体质量增长和成活率,研究了不同放养密度对凡纳滨对虾稚虾免疫指标及生长的影响。统计分析发现,试验过程中水体理化因子均在适宜范围,各处理间水质因子的差异不显著;对虾的PO活力、Ua和AKP活力均随着密度的增加而降低,SOD活力则反之;对虾的体质量增长、体质量特定增长率和成活率随着密度的增加而降低,成活率差异显著（P〈0.05）。结果表明,凡纳滨对虾（体长〈4.8 cm或体质量〈1.2 g）在密度为1 200～1 800尾.m-3时,密度胁迫可明显影响其免疫指标和生长。     

Effect of stocking density and protein/fat ratio of the diet on the growth of Dover sole (Solea solea)

Two hundred and fifty soles (30 g initial weight) were randomly stocked in 12 tanks (recirculation system) at two different stocking densities (2.3 and 1.3 kg m^?2) and fed on two different diets (50% and 54% of crude protein and 21% and 18% of total lipid, respectively, for diets A and B) with triplicate tanks for treatment. The trial lasted for 300 days. Fish stocked at low density showed a significantly higher weight gain than the fish reared at 2.3 kg m^?2 density (94.1±7.4 vs. 78.9±8.2 g, P<0.01) with a specific growth rate (SGR) of 0.46±0.11 and 0.43±0.16 (P<0.01) respectively. Feed conversion ratio (FCR) was more favourable for lower density groups (2.50 vs. 2.64, P<0.01). Diet B led to a higher final weight (124.1 vs. 110.2 g, P<0.01) and a better feed utilization (FCR: 2.49 vs. 2.65, P<0.01). Except for the lipid content, which was higher in the low‐density group (2.6% vs. 2.3%, P<0.05), proximate composition of sole's muscle was not influenced by treatments. Dover sole reared at low stocking density showed higher monounsaturated fatty acid (35.27% vs. 34.40%, P<0.01) and lower saturated fatty acid (24.36 vs. 26.13%, P<0.01) contents, and lower atherogenic (0.67 vs. 0.75, P<0.01) and thrombogenic (0.28 vs. 0.32, P<0.01) indexes.     

Effects of stocking density on survival, growth, size variation, and production of Tilapia fry

In aquaculture, controls of size (length and weight) and production of fish are two important tasks to meet the market demands, and increasing the stocking density is a way of dealing with the problem of land shortage. In this study, tilapia fry were stocked at the densities of 0.1, 0.2, 0.4, 0.8, 1.6 and 3.2 fry I^?1 for an experimental period of 10 weeks. The size, size variation, percentage survival and production were found to be significantly affected by stocking density, but not for condition factor. The simple linear regression model, after the logarithmic transformation, was appropriate for the relationship between size and experimental period. The percentage survivals at all stocking densities were high (> 95%), especially at the stocking density of 0.4 fry I^?1 and less (100%). At the higher densities, percentage survival and experimental periods were anti-logistically related. At the end of the experiment, there was a negative relationship between the logarithms of size and the logarithms of stocking density, but a positive relationship between the logarithms of production and the logarithms of stocking density.     

Effects of stocking density on growth and non-specific immune responses in juvenile soft-shelled turtle, Pelodiscus sinensis

To investigate the influence of stocking density on the growth and non‐specific immune responses of juvenile soft‐shelled turtle, Pelodiscus sinensis, three groups of turtles (initial body weight 74.2±12.2 g) were reared in 80 cm (L) × 40 cm (W) × 30 cm (H) tanks for 35 days at three stocking densities (StD), which were 1 individuals (ind.) tank⁻¹ (3.13 ind m⁻²) for D1, 4 ind. tank⁻¹ (12.5 ind m⁻²) for D2 and 6 ind. tank⁻¹ (18.75 ind m⁻²) for D3 respectively. D1 was the control group. Turtles were weighted individually at the beginning and at the end of the trial. At the end of the rearing trial, non‐specific immune parameters were determined. The results showed that the heterophil:lymphocyte ratio (HLR) increased and the total plasma protein decreased with increasing StD, suggesting a stress response. Specific growth rate (SGR) significantly decreased with increasing StD. Non‐specific immune indicators such as blood cell phagocytic activity, serum haemolytic activity and serum bacteriolytic activity increased clearly at a higher StD, indicating a pattern of immunoenhancement. The results indicated that at StDs of 4 and 6 ind. tank⁻¹, non‐specific immune responses were not suppressed compared with the control, but were inversely enhanced at the cost of growth reduction. A possible energy‐based trade‐off between growth and constitutive immunity may exist in soft‐shelled turtles.     

Effects of temperature, stocking density and diet on the growth and survival of juvenile Mithraculus forceps (A. Milne Edwards, 1875) (Decapoda: Brachyura: Majidae)

Mithraculus forceps (A. Milne Edwards) has demonstrated a great potential for ornamental aquaculture and the present study tests the effects of temperature, stocking density and diet on the survival and growth of M. forceps juveniles. For 28 days post metamorphosis (DPM), the newly metamorphosed juveniles were reared at two temperatures (25±0.5 or 28±0.5°C), stocked at five densities (1, 5, 15, 30 or 60 crabs ring⁻¹; approximately 226, 1132, 3395, 6791 or 13 581 crabs m² respectively) and fed with commercial pellets (CP), microalgae (Amphora spp.), live newly hatched Artemia nauplii (NHA), frozen Artemia nauplii (FNHA), or combinations of each of these diets with NHA. At the end of the temperature experiment, carapace width of the crabs cultured at 28°C was significantly larger than the crabs reared at 25°C and average intermolt period was significantly shorter. Increased stocking density had a negative effect on survivorship and growth. Survivorship at the end of the diet experiment was significantly different between the crabs not fed, fed with CP and Amphora and the crabs fed with the other diets. Between the diet treatments, the crabs fed with NHA+Amphora were significantly larger than the ones fed with NHA+FNHA, NHA, FNHA and NHA+CP, and these in turn larger than ones fed with Amphora.     

Intra-cohort cannibalism among larval stages of perch (Perca fluviatilis)

Cohorts of perch larvae, hatched within 24 h, developed into a bimodal body size distribution as early as 6 days after commencement of external food uptake. At this development stage, intra-cohort cannibalism occurred among larval perch individuals of larval stage V (body size: 10.5±0.26 mm, 95% c. l.) on smaller siblings. In experimental trials the consumption rate (C: no. of prey/predator·hour) increased exponentially with size of predatory perch (L: mm) and at 21°C was expressed by the relationship log C=3.406·log L-3.848 (n=10, r²=0.98, P<0.001). For predatory perch in larval stage V, consumption rate was reduced when Daphnia pulex were added, while not in later stages. Perch larvae experimentally forced to live as true piscivores without additional food items developed from stage V to stage IX (15.8±1.34 mm) within the same time as those fed on Daphnia alone, but with increased mortality.     

Effect of stocking density on growth performance of juvenile sea cucumber Holothuria tubulosa (Gmelin, 1788)

Stock density is one among the most important factors in aquaculture that directly influences the growth of organisms; however, there is limited information about the effects of stocking density on growth performance of sea cucumber Holothuria tubulosa (Gmelin, 1788) that has a commercial potential and represents a new species for aquaculture. In this study, we investigated the effect of stocking densities on the growth performance of juvenile H. tubulosa (40.3 ± 3.34 g) in laboratory conditions. Stocking densities were selected as 6, 15 and 30 ind m^?2 with total biomass 253.3 ± 0.18, 601.2 ± 0.11 and 1201.4 ± 0.15 g m^?2 respectively. We monitored the growth by wet weights and calculated the growth performance through weight gain, growth rate, specific growth rate, relative weight gain, coefficients of variation and survival rate during 8 weeks of research period. We found that individual mean weight gain in 6 ind m^?2 group was approximately 29.53 g while it was 3.03 g and ?4.36 g for 15 ind and 30 ind m^?2 groups respectively. Results have shown that the specific growth rate tends to decrease as the number of individuals in unit area increases. The final mean weight, growth rate, specific growth rate, relative weight gain and coefficients of variation were significantly different among treatment groups. In conclusion, a density of 6 ind m^?2 is recommended for stocking juvenile H. tubulosa under rearing conditions. Stocking density of 15 ind m^?2 is not favourable for long term as the growth rate is negligible where 30 ind m^?2 should be avoided in tank‐based rearing units.     

Effects of stocking density on the growth performance,physiological response and intestinal microbiota of juvenile Echiura worms (Urechis unicinctus)

Aquaculture of the Echiura worm Urechis unicinctus has developed rapidly in recent years. However, the artificial cultivation technology remains to be perfected. In this study, the effects of stocking density on the growth performance, physiological responses and intestinal microbiota of U. unicinctus juveniles were evaluated. Juvenile worms were randomly stocked at densities of 200 U (U. unicinctus/m³), 500 U, 1,000 U and 2,000 U, in aquariums. The results indicated that the contents of triglycerides, glucose, total cholesterol, lactic acid, alkaline phosphatase, acid phosphatase and aspartate transaminase in the coelomic fluid of U. unicinctus juveniles were significantly enhanced with increasing stocking density. The digestive enzyme activities increased with increasing stocking density from 200 U to 1,000 U, before exhibiting a significant decrease in the 2,000 U group. In contrast, the antioxidant capacity of U. unicinctus juveniles was suppressed under high stocking density conditions. In case of the intestinal microbiota of U. unicinctus juveniles, Actinobacteria were more abundant in the 200 U group; SJA15, Gluconobacter and OP81 were higher in the 1,000 U group; Burkholderiales and Limnohabitans were enriched in the 2,000 U group. The highest and lowest survival rates of the U. unicinctus juveniles were recorded in the 500 U and 200 U groups respectively, and high stocking densities negatively affected the individual growth performance. In summary, due to the highest survival rate and appropriate growth performance and physiological responses, 500 U was considered to be the optimal stocking density for the cultivation of U. unicinctus juveniles.     

Effects of diet, stocking density and environmental factors on growth, survival and metamorphosis of clam, Paphia malabarica (Chemnitz) larvae

A series of experiments were conducted to evaluate the effects of diet, stocking density and environmental factors on the growth, survival and metamorphosis of short neck clam Paphia malabarica larvae. These experiments examined the following factors: diet [ Isochrysis galbana , Nannochloropsis salina and a mixture of I. galbana and N. salina (1:1 w/w)], stocking density (1, 3, 5 and 7 larvae mL⁻¹), light intensity (unshaded, partially shaded and fully shaded) and water filtration (unfiltered and sand filtered). Results indicated that N. salina could replace 50% of I. galbana as a food source for the clam larvae with an increase in growth, survival (47.2%), metamorphosis (33.5%) and early settlement. Larval growth decreased significantly with increasing stocking density. A density of 1–3 larvae mL⁻¹ appeared to be optimal for normal growth of clam larvae. Neither diet nor stocking density used in the study had a significant effect on larval survival. Under partially shaded (light intensity=1000–5000 lx) and fully shaded (light intensity <1000 lx) conditions, larval growth was significantly faster than under direct sunlight (unshaded). Larvae grew significantly faster in the unfiltered water than in the filtered water.