Effects of Broodstock Size and Source on Ovarian Maturation and Spawning of Penaeus monodon Fabricius from the Gulf of Thailand

The effects of broodstock source (pond-reared and wildcaught from shallow waters) and prawn size (large—weight >120 g, and small-weight < 110 g) on ovarian maturation and reproductive success of Penueus monodon were evaluated. Large females underwent stage IV ovarian maturation and spawned with greater success than did small prawns. Both pond-reared and wildcaught females of the same size exhibited comparable maturation and spawning success. Large females rematured and spawned more frequently than small ones. Total eggs produced by large prawns was significantly greater than for small prawns; nevertheless, prawn source and size had no significant influence on amount of eggs spawned per spawning event. Egg quality varied greatly in terms of percent fertilization, hatch rate, and metamorphosis to first protozwa stage.     

Effects of dietary fatty acids on the production and quality of eggs and larvae of Atlantic cod (Gadus morhua L.)

Cultivated Atlantic cod (Gadus morhua) entering their first year of gamete maturation were fed diets with different levels of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) for 6.5 months prior to commencement of spawning. Gravid females were stripped three times: at the beginning, peak and end of spawning. Lipid composition and egg and larval quality of 34 family crosses were investigated. Results indicated that ARA uptake into eggs from broodstock diet was highly efficient achieving proportions of ARA up to 84% higher in eggs than in the diet. EPA was 42–76% higher, and DHA was 155–173% higher in eggs than in diets. Cod fed the diet with the lowest EPA/ARA ratio had the greatest egg production. Eggs from fish on a diet with high ARA level had significantly higher fertilization and hatching success than those fed low levels of ARA. This diet produced on average 71 viable eggs g^?1 female compared with 32.5 and 4 eggs in diet B and C, respectively. Furthermore, larval survival until 8 days posthatch was higher in diets with lower ARA levels. The combined results showed that ARA dietary supplementation and low EPA/ARA ratio yielded a greater number of viable larvae kg^?1 female.     

Effect of prepared diet on the induction of precocious maturation in Pleoticus muelleri Bate (Crustacea, Penaeoidea)

Experiments were conducted comparing the reproductive performance of ablated female shrimp Pleoticus muelleri fed either a fresh frozen diet (ND) (clam, prawn, squid) and the same diet supplemented with 15% of an artificial diet (SD) (54% protein, 13% lipid, 7% moisture). The shrimp were maintained in 3500‐L tanks (12 h light‐12 h dark photoperiod, temperature 18–20°C, pH 7, salinity 31 g L^?1, ammonium <0.2 mg L^?1, and sea water exchanged at 100% per day) for 45 days. Significant differences in weight gain were determined between ablated females fed ND (37.2%) and SD (26.4%). No significant differences in the average duration of the intermolt period (19±2 days) were recorded. Females fed SD showed signs of maturation 20 days after ablation, with spawning occurring 1 day later, as long as ablated females fed ND reached maturation 4 weeks after did not occur. The number of eggs per spawn varied from 136 000 to 345 000; the percentage viability ranged between 39.3% and 99.3% with an average of 78.5%. The results indicated that a suitable formulated diet together with eyestalk ablation promotes maturation of P. muelleri in captivity.     

Effect of dietary soybean lecithin on reproductive performance of Chinese mitten crab Eriocheir sinensis (H. Milne-Edwards) Broodstock

The effect of increasing levels of dietary phospholipids (PL) on the ovarian development and reproductive performance of Chinese mitten crab Eriocheir sinensis were investigated using four semipurified formulated diets supplemented with 0%, 1.2%, 2.4%, and 3.6% PL. Four groups of 40 females, with an average individual body weight of 95–120 g, were fed the experimental diets for a period of 7 months. Male crabs were introduced into the female rearing system in March, and mating, spawning, and egg hatching occurred in the following month. After 10 weeks of feeding, females fed the diet with 2.4% PL had a significantly higher gonadosomatic index (GSI) than females fed the diet with 0% PL, whereas females fed the diet with 1.2% PL had a significantly higher hepatic moisture content and lower hepatic lipid content than the other groups (P < 0.05). After mating, the spawning rate was higher among females fed diets with 3.6% and 2.4% PL (95% and 92%, respectively) compared with females fed diets with 0% and 1.2% PL (both 81%). The results showed that egg production (total number of eggs/female) and fecundity increased with increasing dietary PL level, with females fed diets with 0% and 1.2% PL supplementation having significantly lower values than females fed the diet with 3.6% PL (P < 0.05). In conclusion, our results suggest that dietary PL supplementation has a positive effect on ovarian development and reproductive performance of E. sinensis broodstock. Further study should aim to investigate the optimal PL level in the broodstock diet of E. sinensis in respect to offspring quality.     

Reproductive performance and offspring quality in mud crab (Scylla paramamosain) broodstock fed different diets

A 2-month feeding trial was conducted toevaluate the reproductive performance andoffspring quality of mud crab (Scyllaparamamosain) females fed either a mixture offresh food items (squid, shrimp, trash fish andArtemia biomass) or two experimentaldiets developed for penaeids. Before testinitiation, mud crab females with an averageindividual wet weight of 200–300 g wereacclimated for 2–3 days and reared together inone concrete tank of 2.0 × 0.5 × 8 m untilspawning. After spawning, the spent spawnerswere unilaterally eyestalk ablated and randomlydivided (20 animals/treatment) over three tanksof the same size and subjected to the dietarytreatments. Spent spawners were used toeliminate the effect of feeding history.There were only minor differences inreproductive performance between dietarytreatments. No differences were observed in theduration of the latency period from eyestalkablation to spawning. Fecundity was onlymarginally higher for the broodstock fed thecontrol diet. Also egg quality seemed onlyslightly affected by the treatments. Egghatching rates were slightly higher in crabsfed the formulated diets compared to thosecrabs fed the fresh diet. The onlystatistically significant difference (p < 0.05) observed however was in egg hatchingrate between the control diet and diet A2. Incontrast, the crabs fed the fresh diet producedstronger larvae as determined by a starvationtest.We therefore conclude that artificial dietsresulted in reproduction success comparable tothe use of fresh food. The nutritionalcomposition of the artificial diets couldhowever be improved in order to produce larvaeof optimal quality. Based on our researchfindings, the protein level and n-3 HUFA levelin the diet warrants further investigation inthis respect.     

Diet and Food Assimilation by Channel Catfish and Malaysian Prawns in Polyculture as Determined by Stomach Content Analysis and Stable Carbon Isotope Ratios 1

Stable carbon isotope ratios (?³C) and stomach contents were used to determine the diet of channel catfish (Ictalurus punctatus) and freshwater Malaysian prawns (Macrobrachium rosen-bergii) in polyculture. Catfish stomach contents were dominated by formulated rations. Macrophyte fragments and catfish ration were predominate in prawn stomachs. Catfish ?¹³C ratios became lighter from June to October, which paralleled the change in ?¹³C ratio of the formulated feeds fed to the fish. Prawn ?¹³C ratios became heavier from June to October with a change in diet from seston to aquatic macrophytes and formulated catfish feed. Formulated feeds contributed 68-99% of catfish growth, and “natural” pond biota, principally insects, the remainder. Prawns depended to a greater extent on the autotrophic food web for their diet. Seston and macrophytes contributed 18-75% of prawn growth, and formulated feeds the remainder. The prawns fed on seston at small sizes (<7 g) and consumed more aquatic macrophytes and formulated catfish ration at larger sizes (<7 g).     

Growth and metabolic responses of juvenile Macrobrachium nipponense to different dietary carbohydrate levels

It remains controversial whether carbohydrate can be efficiently used by crustaceans. Six isonitrogenous and isolipid diets were formulated containing 50–350 g kg^–1 corn starch and were fed to juvenile prawns (mean weight, 0.133 ± 0.003 g) for 56 days in five replicates. Prawns fed 50–150 g kg^–1 corn starch attained significantly greater weight gain. Digestive enzyme activities were significantly affected by dietary corn starch level. Hepatopancreatic and muscle glycogen levels peaked in prawns fed 350 g kg^–1 and 150 g kg^–1 corn starch content, respectively. Prawns fed 350 g kg^–1 corn starch had a significantly higher haemolymph glucose level than that in the other groups. Hepatopancreatic hexokinase (HK) activity increased significantly as corn starch level was increased. Hepatopancreatic pyruvate kinase (PK) activity of prawns fed the 150 g kg^–1 and 250 g kg^–1 corn starch was significantly higher than that of prawns fed 50 g kg^–1 corn starch. Including carbohydrate in the diet promoted increased lipogenic activities (glucose‐6‐phosphate dehydrogenase and malic enzyme) in the hepatopancreas. Hepatopancreatic HK and PK mRNA expression levels had similar trends with their activities. The 350 g kg^–1 corn starch level induced the highest glucose‐6‐phosphatase and pyruvate carboxylase mRNA expression levels. Overall, moderate metabolic adaptations for using dietary corn starch were detected in Macrobrachium nipponense; however, a high proportion (>150 g kg^–1 ) of corn starch in the diet may reduce growth.     

Enhancement of reproductive performance in shrimp Litopenaeus vannamei (Boone, 1931) by supplementation of Ulva clathrata meal in maturation diet in two commercial hatcheries

The effect of supplementing dehydrated seaweed Ulva clathrata (20 g/kg) in the squid fraction of a formulated fresh diet on the reproductive performance of Litopenaeus vannamei broodstock was evaluated in two commercial hatcheries (A and B). The origin of broodstock, use of ablation on females, tank/culture conditions (for maturation, spawning, and larval rearing) were different between hatcheries. Daily mortality was higher (p < .01) for females in the control group compared to Ulva‐fed group of hatchery A, where females were ablated. No differences in mortality were found for unablated females in hatchery B, or with males from either hatchery. In hatchery A, broodstock fed Ulva produced more eggs (an increase in +5% compared to control, p < .05) and nauplii per female (+18%, p < .01). In hatchery B, broodstock fed Ulva produced significantly more eggs (+26%, p < .05) and nauplii per day (+33%, p < .05). In hatcheries A and B, eggs from broodstock fed Ulva had increased hatching rates (+13 and +7%, respectively, p < .001 in both cases). The number of spawns per day had a tendency to be higher in broodstock fed Ulva in both hatcheries, but the difference did not reach statistical significance (+14% for hatchery A and +20% for hatchery B). Dehydrated U. clathrata appears therefore as a functional additive in L. vannamei maturation diets that enhances the reproductive performance at commercial scale, regardless of the management conditions.     

Effects of taurine levels in broodstock diet on reproductive performance of yellowtail Seriola quinqueradiata

The effect of dietary taurine was investigated on reproductive performance in yellowtail Seriola quinqueradiata. Two-year-old fish of average body weight 6.1kg were fed on diets containing three levels of taurine (T-0, T-0.5 or T-1.0%) for 5 months prior to spawning. For spawning investigations, fish were induced to maturity by human chorionic gonadotrop in injection (600 IU/kg-fish) and artificially inseminated. Oocyte growth improved significantly (P<0.05) with the increase of dietary taurine. The collection of eggs from females reared on the T-0% diet was not successful. The success rate of spawning for females fed on T-0.5 and 1.0% diets was one out of six, and six out of seven, respectively. The taurine levels of the liver and serum in the T-0% diet group were much lower than that in the T-0.5 and T-1.0% diet groups (P<0.05). Fish fed the T-0% diet showed higher contents of serine in the liver and serum. The taurine content of the ovary was not significantly different among the different dietary treatments. These results indicate that taurine has a positive effect on the improvement of spawning performance of yellowtail.     

Maturation and spawning performance of pond-reared Penaeus merguiensis in different combinations of temperature, light intensity and photoperiod

The combined effects of temperature (23 and 27 °C), light intensity (1100 and 2 lux or ≈ 21.5 and 0.04 μEinst m^?2 s respectively) and photoperiod (10 h light/14 h dark and 14 h light/10 h dark) on ovarian maturation and spawning performance of ablated pond‐reared Penaeus merguiensis were investigated in a 51‐day experiment. The results showed that temperature was the most influential factor, followed by light intensity, whereas the effect of photoperiod was minor. As the maturation process progressed, the effects of temperature and light intensity became stronger while that of photoperiod became less significant. Temperature significantly affected all the reproductive parameters assessed. Prawns in the 27 °C treatments outperformed those in the 23 °C treatments (P < 0.05). The effect of light intensity was found to have a significant effect (P < 0.05) only on the proportion of spawners (prawns that spawned) and spawning rate. More prawns spawned at a higher rate under dim light (2 lux) than under strong light (1100 lux). Photoperiod affected only the proportion of prawns reaching stage III of ovarian development (P < 0.05). There were interactions between temperature and light intensity affecting the proportion of prawns reaching stage III and, although not significantly, the proportion of spawners (P = 0.177), fecundity (P = 0.134) and survival (P = 0.061). Overall, it is recommended that a combination of 27 °C, 2 lux and 10 h light/14 h dark is suitable for the maturation of pond‐reared P. merguiensis. There were indications that temperature can be used to control the rate of ovarian maturation. Also, it is possible to increase light intensity up to 1100 lux in P. merguiensis hatcheries if prawns are ablated.     

Effects of replacing dietary fish oil and squid liver oil with vegetable oils on the growth,tissue fatty acid profile and total carotenoids of the giant freshwater prawn, Macrobrachium rosenbergii

A feeding trial was conducted to investigate the complete substitution of either fish oil (FO) or squid liver oil (SLO) with crude palm oil (CPO), canola oil (CO) sunflower oil (SFO) or linseed oil (LO), as the sole added lipid source in diets fed to triplicate groups of giant freshwater prawn, Macrobrachium rosenbergii (initial weight = 0.42 ± 0.01 g) for 6 weeks. Prawns fed the CO or SLO diets showed significantly higher (P < 0.05) specific growth rate than those fed the FO or CPO diets. The feed conversion ratio of the prawns was significantly better when fed the CO diet, compared with the FO, CPO, SFO and LO diets. The muscle eicosapentaenoic acid content of prawns fed the vegetable oil (VO) diets were not significantly different (P > 0.05) from those fed the FO diet, although all VO‐based diets led to a significantly lower docosahexaenoic acid content compared with prawns fed the FO or SLO diet. The whole‐body total carotenoid content was significantly lower for prawns fed the SLO diet compared with prawns on the CO or CPO diets. The successful use of VO instead of marine‐based oils in prawn diets will likely reduce feeding costs associated with M. rosenbergii aquaculture.     

MATURATION,REPRODUCTION, AND GROWTH OF Penaeus vannamei AND P. stylirostris FED NATURAL DIETS

A variety of natural foods have been reported to induce ovarian maturation of penaeid shrimp. In this study, conducted from 19 June to 11 September 1980, four single-food diets (clams, shrimp, squid, and worms) and one composite diet consisting of all four foods were fed to Penaeus vannamei in 3.7-m diameter indoor circular tanks. The shrimp, averaging 28 g, were stocked at a rate of 6.9 m^-2 with a 1:1 male to female ratio. Unilateral eyestalk ablation was performed on half of the females in each tank. Tanks received one turnover of water volume daily and the water temperature and salinity averaged 27.0°C and 28.6 ppt, respectively. Daily photoperiod was maintained at 13 hours of light. Ovarian maturation, spawning, molting rate, and survival were monitored daily and growth and gonad size were measured at termination. The composite diet was the best overall diet, while squid was the best single-food diet, followed by shrimp, worms, and clams. No maturation of unablated females was observed with the exception of one female that developed to stage 3. Although the size of the shrimp was considered marginal for spawning, 5 mated females were observed, but only one (squid treatment) produced viable nauplii. After termination of this study, all shrimp were fed the composite diet for 41 days. During this period, ovarian maturation and spawning occurred in the previously unproductive treatment receiving only clams, and growth rate of shrimp in all previously single-food treatments increased 4 to 7 fold. The composite diet was also fed to two tanks of P. stylirostris (mean initial weight = 45.4 g) for a period of 118 days. During that time, 50 spawns were obtained with up to 3 spawns per female. A total of 4.3 × 10⁵ P. stylirostris nauplii were produced.     

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.     

Production Characteristics of All‐male and Mixed‐sex Giant River Prawns,Macrobrachium rosenbergii,Grown in Earthen Ponds in Kentucky and Mississippi USA

Production and population characteristics of monosex male (all‐male) giant river prawns, Macrobrachium rosenbergii, were compared with a normal (mixed‐sex) population in separate studies in Mississippi and Kentucky (USA) under low and high density stocking conditions, respectively. In Study 1 (Mississippi), juvenile prawns were stocked into eight 0.05–0.06 ha ponds at 24,700/ha. The mean stocking weight of all‐male was 0.34 g and mixed‐sex was 0.39 g. Prawns were fed 23% crude protein “range cubes” and harvested after 120 d for the all‐male prawns and 112 d for mixed‐sex prawns. In Study 2 (Kentucky), juvenile prawns from each group were stocked into six 0.04 ha ponds at 60,000 juveniles per hectare. The mean stocking weight for all‐male was 0.38 g and for mixed‐sex juveniles was 0.34 g. Prawns were fed a commercial sinking pellet (33% protein) once daily at a standardized rate and harvested after 105 d. In both locations survival of mixed‐sex prawns and all‐male prawns was not significantly different and the final average weight of all‐male prawns was significantly greater than the average weight of mixed‐sex prawns. For the study in Kentucky, total production was not significantly different between treatments, whereas in Mississippi total production in the all‐male ponds was significantly higher than in the mixed‐sex ponds. For both studies, the production size index of all‐male prawns was significantly greater than that of mixed‐sex prawns. In terms of population structure, in all‐male ponds there was a significant increase in orange claw (OC) males compared with the mixed‐sex ponds both as a percent of sex and a percent of total population. The increase in OC numbers in all‐male populations may be due to a lack of females to stimulate the transition of males to the final, sexually mature, blue claw stage. As target weights increase from 20, 30, and 40 g, the all‐male populations were increasingly superior in terms of production (kg/ha) of those target sizes. The economic benefit of all‐male over mixed‐sex populations will be principally based on an examination of tradeoffs that primarily consider the cost difference of juveniles relative to the price differences for different final harvest weights.     

Preliminary Studies of Artificial Spawning of Channel Catfish as Male-Female Pairs or All-Female Groups in Recirculating Systems

Abstract— Channel catfish Icralurus punctatus are commonly spawned for research purposes by pairing of a hormonally treated female with a male in flow-through aquaria. A technique that allows hormonal induction of ovulation in females without pairing would accelerate genetic improvement and production of hybrid catfish. Over a 3-yr period (1994, 1995, and 1996) we conducted a series of trials to demonstrate the potential for artificial spawning in recirculating systems, and in 1996 we included trials with grouped females in addition to male-female pairs. Females were induced to spawn with injection of synthetic leuteinizing hormone-releasing hormone, and those that ovulated were stripped and the eggs were artificially fertilized. During 1994 and 1995, all fish were spawned by pairing, and in 1996, half of the females were spawned by pairing and half were grouped in tanks without males. Spawning success (percent of females that produced eggs), latency (time between injection and ovulation), and percent fertilization were observed for the paired and grouped trials. Spawning success was 36% in 1994 (N= 36). 22% in 1995 (N= 54). 41% in 1996 (N= 27). and 58% for grouped females (N= 26). The latency period was 113 ± 69 h in 1994, 109 ± 57 h in 1995, 44 ± 8 h in 1996, and 50 ± 9 h for grouped females. Percent fertilization was 16 ± 26% for eggs stripped in 1994, 72 ± 25% in 1995, 43 ± 20% in 1996, and 16 ± 37% for grouped females. In 1995, water quality problems were associated with high mortality of females (24 of 44 females; 4 of 44 males). The metabolic demands of final oocyte maturation in combination with methemoglobinemia caused by high nitrite levels could account for the increased vulnerability of females. These trials indicate that with adequate biofiltration, artificial spawning is possible in recirculating systems and with females grouped rather than paired. Further research on hormone dosage and timing of egg stripping will increase the utility of grouped spawning of channel catfish.     

Reproductive Performance of Macrobrachium rosenbergii Females in Captivity

Abstract.— The breeding frequency, fecundity, egg hatchability, larval output and viability of pond-reared, mature Macrobrachium rosenbergii females were individually followed up during 180 d. Sexually mature prawns were maintained under controlled laboratory conditions (28.7 C and 12-h light/d) in a 190-L freshwater recirculation system and fed a formulated diet. Ovarian development, moulting and spawning events were checked daily. At least six consecutive moults were recorded for each of the 18 females. The duration of the intermoult period averaged 27.5 d and was not affected by ovarian development or spawning, but intermoult periods followed by spawning had significantly lower growth rates. From a total of 126 moulting events recorded, egg laying successfully followed 76 (60.3%) of them. The number of eggs per spawn (NES) varied from 26,587 to 74,775 for females weighing 20.0 to 55.8 g. The relationship between NES and female size (W; in g) was found to be NES = 484 + 1454W ( r ²= 0.74). Results suggest that the number of viable larvae produced per egg clutch may be increased by in vitro incubation, as the losses of eggs, which usually occur under in vivo incubation, are prevented. The present study illustrates that under adequate and stable rearing conditions, M. rosenbergii females are able to spawn up to five times during 180 d, in comparison to three to five times per year as reported for wild prawn populations.     

Evaluation of partial replacement of live and fresh feeds with a formulated diet and the influence of weaning <Emphasis Type="Italic">Panulirus ornatus</Emphasis> phyllosomata onto a formulated diet during early ontogeny

We have evaluated the potential of a formulated diet as a replacement for live and fresh feeds for 7-day post-hatch Panulirus ornatus phyllosomata and also investigated the effect of conditioning phyllosomata for 14–21 days on live feeds prior to weaning onto a 100% formulated diet. In the first trial, the highest survival (>55%) was consistently shown by phyllosomata fed a diet consisting of a 50% combination of Artemia nauplii and 50% Greenshell mussel, followed by phyllosomata fed 50% Artemia nauplii and 50% formulated diet and, thirdly, by those receiving 100% Artemia nauplii. The second trial assessed the replacement of on-grown Artemia with proportions of formulated diet and Greenshell mussel that differed from those used in trial 1. Phyllosomata fed a 75% combination of formulated diet and 25% on-grown Artemia and 50% on-grown Artemia and 50% Greenshell mussel consistently showed the highest survival (>75%). Combinations of Greenshell mussel and formulated diet resulted in significantly (P < 0.05) reduced survival. In trial 3, phyllosomata were conditioned for 14, 18 or 21 days on Artemia nauplii prior to weaning onto a 100% formulated diet, which resulted in survival rates that were negatively related to the duration of feeding Artemia nauplii. In the final trial, phyllosomata were conditioned for 14 days on live on-grown Artemia prior to weaning onto one of three formulated diets (one diet with 44% CP and two diets with 50%). Phyllosomata fed a 44% CP diet consistently showed the highest survival (>35%) among all treatments, while those fed a 50%-squid CP diet showed a significant (P < 0.05) increase in mortality at day 24. The results of these trials demonstrate that hatcheries can potentially replace 75% of live on-grown Artemia with a formulated diet 7 days after hatch. The poor performance associated with feeding combinations of Greenshell mussel and formulated diet, and 100% formulated diet as well as conditioning phyllosomata for 14–21 days on live feeds prior to weaning onto a formulated diet highlights the importance of providing Artemia to stimulate feeding.     

Fatty acid and amino acid composition of eggs, muscle and midgut glands of freshwater prawns, Macrobrachium rosenbergii (de Man), raised in fertilized ponds, unfertilized ponds or fed prepared diets

Fatty acid and amino acid profiles were determined in three tissues (eggs, muscle and midgut glands) from freshwater prawns, Macrobrachium rosenbergii (De Man), raised unfed in ponds with no organic fertilization, unfed in ponds with organic fertilization or fed a formulated, pelleted diet. Amino acid profiles of tail muscle and eggs were not treatment-dependent. Comparison of amino acid profiles of the diet with those of tissues of animals fed that diet suggest that dietary levels of arginine, histidine, methionine, and especially lysine may be suboptimal. Fatty acid profiles of the midgut gland, tail muscle, and to a lesser extent, eggs reflected the fatty acid composition of the diet in the fed treatment, the organic fertilizer material in the fertilized treatment and natural food organisms in the unfed treatment. Direct consumption of organic fertilizer particles by the prawns is supported by these data. Selective retention of essential fatty acids appears likely in all three treatments. Comparison of the fatty acid composition of prawn eggs and muscle tissue with that of the pelleted diet indicates that 18: 3(n-3), 20: 5(n-3), and especially 20: 4(n-6) are probably below optimal levels. However, under practical culture conditions, prawn growth may not be significantly reduced because of relatively low dietary requirements and contributions from natural foods in the ponds.     

Biological performance of Octopus vulgaris in ‘integrated aquaculture’ models: effect of two potential fresh diets,sex and sexual maturation during the grow‐out phase

Two fresh diets were tested on the biological performance of males and females of Octopus vulgaris under industrial rearing conditions in floating cages. The presence of females could potentially release paralarvae to the natural environment (‘integrated aquaculture’). Octopuses were fed on a single diet of bogue (aquaculture by‐product), and on a mixed diet (60–40% crab‐bogue), in two trials. In Trial 1 (918 ± 125 g), growth was higher in octopuses fed on the mixed diet (1.9–2.0%d^?1) than in those fed on the bogue diet (1.8–1.9%d^?1) irrespective of sex, and mortality was 3% regardless of sex and diet. In Trial 2 (1483 ± 269 g), growth was higher in males fed on the mixed diet (1.8%d^?1) than in males fed on the bogue diet (1.4%d^?1), both higher than females (1.1–1.3%d^?1), and mortality was 22–28% regardless of sex and diet. Best biological performance in trial 1 was related to the lack of functional maturation in females, evidence by the low average gonadosomatic index (2.0–3.6%) in comparison with trial 2 (8.8–11.4%), regardless of diet. No correlations between final weight and sexual maturity indices were found, so the length of the rearing period to maximize biomass increment or to release paralarvae depends on functional maturation in females.     

Induced winter spawning and culture of larvae of the blue crab, Callinectes sapidus rathbun

Female blue crabs were induced to produce eggs out of their normal spawning season. One group of crabs, held in the laboratory at 19° C, was fed every 7 days; another group, held at 15° C, was offered food at the same interval. Photoperiod simulated ambient winter conditions in both groups. Of ten crabs held at 19° C, two produced egg masses and one died when spawning was about to commence. Among those crabs not producing egg masses during the experiment, ovarian development at 19° C proceeded further than among those held at 15° C.Survivorship of larvae from induced eggs raised on a rotifer diet was comparable with that for naturally spawned larvae through the first 28 days of development.Zoeae survived well to metamorphosis when fed a diet of rotifers during the first two stages, followed by Artemia salina nauplii. However, only six zoeal stages were present instead of the usual seven. Possible explanations for this observation include genetically controlled variation, variation due to origin of eggs (induced), or effect of diet.Survivorship and growth were not adversely affected when synthetic sea water was used as the culture medium.