Growth response of African catfish,Clarias gariepinus (B.), larvae and fingerlings fed protease‐incorporated diets

African catfish, Clarias gariepinus (B.), is one of the promising freshwater fish species in African aquaculture but the expansion of its farming needs more production of its larvae. The use of live food organisms at first feeding for larvae is still obligatory. That increases the cost of larvae production. Hence, the incorporating of exogenous enzymes especially protease in artificial microdiets may provide affordable alternatives for enhancing the larvae performance. The present study was carried out to evaluate the growth and survival of larvae or fingerlings of African catfish fed artificial diets incorporated with different protease levels. Four artificial diets were formulated and enriched with protease enzyme at levels of 0.0, 750, 1,000, and 1,250 unit/kg diet; after that diets were made into crumbles (100–200 µm diameter). After absorption of the yolk sac, diets were offered to fish larvae (3.6 ± 0.2 mg) in triplicates as a starter feed up to apparent satiation every two hours for 30 days. In another treatment, fish larvae were fed on newly hatched Artemia nauplii (2,500 Artemia/L) as a starter food. In another experiment, African catfish fingerlings (10.1 ± 1.6 g) were fed on the same diets up to satiation twice a day for 2 months. It was noticed that the dietary protease improved larval growth and survival but not as Artemia nauplii did where fish larvae fed on Artemia nauplii showed highest growth and survival followed by those fed a diet enriched with 1,250 unit/kg diet of protease. The mortality of larvae fed protease‐enriched diets as well as the control diet was occurred mostly at the first week reaching its maximum at the third week. The poor growth was observed with fish larvae fed the control diet. Meanwhile, catfish fingerlings fed protease‐enriched diets showed higher growth over those fed the control diet. The larvae survival (11.0%–41.7%) was enhanced by increasing protease levels and it was lower than that of fingerlings (95.6%–100.0%). Furthermore, protein retention and digestibility were significantly improved with protease supplementation over the control diet especially at a level of 1,000 unit/kg diet. As compared with the previous studies, live food should be used in larvae rearing for the first week after that a starter diet enriched with protease at levels of 1,250 unit/kg diet should be used. In case of fish fingerlings, the dry diets should be enriched with 1,100 unit/kg diet to improve diet digestibility and subsequently enhance their growth.     

Different iodine and thyroid hormone levels between Atlantic halibut larvae fed wild zooplankton or Artemia from first exogenous feeding until post metamorphosis

The iodine concentration in wild zooplankton was 700 times higher than in Artemia and threefold higher in Atlantic halibut Hippoglossus hippoglossus larvae fed wild zooplankton than in those fed Artemia . In larvae fed wild zooplankton thyroxine (T4) and triiodothyronine (T3) concentrations were significantly higher than in those fed Artemia at the commencement of metamorphosis, 68–77 days post hatching. There was no difference in the amino acids phenylalanine and tyrosine levels in larvae fed Artemia in comparison with those fed wild zooplankton. The selenium level was significantly higher in larvae fed Artemia than in those fed wild zooplankton, but concentrations in the prey were not different. The results indicate sufficient amounts of phenylalanine, tyrosine and selenium in Artemia , but indicated a lower thyroid status due to an insufficient iodine supply at commencement of metamorphosis in larvae fed Artemia . This may partly explain the higher frequency of juveniles with complete eye migration and asymmetric pigmentation in the group fed wild zooplankton.     

Response of bighead carp Aristichthys nobilis and Asian catfish Clarias macrocephalus larvae to free-living nematode Panagrellus redivivus as alternative feed

The use of Panagrellus redivivus as live feed for bighead carp and Asian catfish larvae was tested. In experiment 1, carp larvae were given Artemia nauplii (control) or Panagrellus twice daily for 21 days. A third treatment consisted of unfed larvae. The same three treatments were used in experiment 2 plus another with a commercial entomopathogenic nematode (EPN). Bighead carp larvae given Panagrellus in experiment 1 had much lower growth and survival than those fed Artemia nauplii. This could be due to low nematode density (5–30 mL^?1 water) during feeding. The unfed larvae had 100% mortality by days 11–13. In experiment 2, growth and survival of carp larvae given Artemia nauplii (5–10 mL^?1) and Panagrellus (50 mL^?1) did not differ significantly (P > 0.05). All unfed larvae had died by day 13, while larvae fed EPN were all dead by day 8. Two experiments on Asian catfish were likewise conducted. In experiment 1, the catfish larvae were fed Tubifex (ad libitum), Panagrellus (50–100 mL^?1 per feeding) orArtemia (5 nauplii mL^?1 per feeding) three times daily for 14 days. In experiment 2, larvae were fed Artemia alone (10 nauplii mL^?1 per feeding), Panagrellus alone (100 mL^?1 per feeding), or their combination with a 38% protein dry diet twice daily. For both experiments, catfish larvae fed Panagrellus had significantly lower growth and survival than those fed Tubifex or Artemia. The combination of Panagrellus and dry diet created little improvement in the growth and survival of catfish larvae.     

Effects of two Avtemia diets with different contents of polyunsaturated fatty acids on the lipid composition of larvae of Atlantic herring (Clupea harengus

Atlantic herring larvae ( Clupea harengus ) were fed two enriched Artemia diets with different contents of (n-3) highly unsaturated fatty acids (HUFA), one containing low levels of 20: 5(n-3) and no 22: 6(n-3), the other containing substantial levels of both 20: 5(n-3) and 22: 6(n-3). After 30 days of culture, fatty acid compositions of lipid classes in the heads, bodies and eyes of the larvae were analysed. Fish fed Artemia with the low (n-3) HUFA diet lacking 22: 6(n-3) had lower amounts of total (n-3)HUFA and, in particular, of 22:6(n-3) in individual phospholipids and total neutral lipids of heads, bodies and eyes as compared to fish fed Artemia with high levels of (n-3)HUFA. The amount of 22: 6(n-3) in the fatty acids of phosphatidyl-ethanolamine of eyes was particularly susceptible to dietary depletion. The implications of these findings are discussed, particularly in relation to dietary requirements for 22: 6(n-3) during development of neural tissue in predatory fish iarvae.     

Live food mediated vitamin C transfer to Dicentrarchus labrax and Clarias gariepinus

Live food enrichment techniques, using formulated diets and emulsions for improving the nutritional quality of Brachionus and Artemia , were studied as a tool for transferring ascorbic acid (AA) to fish larvae.
Artemia nauplii enriched for 24 h with an experimental emulsion containing 20% HUFA and 0%, 10% and 20% ascorbyl palmitate (AP) were administered to catfish larvae in a 20-day feeding trial. Survival was not affected by the dietary AA, but from day 7 onwards a significantly positive effect of supplemental AA on growth was demonstrated. At the end of the experiment the 20% AP group weighed 30% more than the control (0% AP), i.e. 9.5 and 6.3 mg DW, respectively. Evaluation of the physiological condition was demonstrated by salinity tests. In all three treatments larval growth was relatively low, and it still has to be verified if extra vitamin C in the diet really promotes growth. Seabass larvae fed on AP-enriched rotifers (days 4–12) and Artemia nauplii (days 13–46) showed no significant differences in production characteristics nor in stress resistance, however, for all salinity stress tests the 20% AP group performed better. AA was well incorporated into the predator larvae from the Brachionus feeding onwards.     

Growth and survival of river catfish Mystus nemurus (Cuvier & Valenciennes) larvae fed isocaloric diets with different protein levels during weaning

The growth of river catfish Mystus nemurus (Cuvier & Valenciennes) larvae fed four isocaloric diets (4200 kcal kg^?1) with different protein levels during weaning was determined. Diets containing 45, 50, 55, and 60% protein were formulated by linear programming using amino acid profiles based on that of 2‐day‐old river catfish larvae. Artificial diets were fed to the larvae beginning at day 5 after being initially fed Artemia nauplii for 4 days. The larvae thrived solely on artificial diets from day 8 to day 16. On the other hand, the control larvae were fed Artemia nauplii from day 1 to day 16. Results of the feeding trial showed that growth and survival of M. nemurus larvae given the diet containing 60% protein were high and comparable to those of the larvae given only live food (control). Larvae fed the 55% protein diet had significantly lower growth and survival than the larvae on the control and 60% diets but significantly higher growth and survival rates than did larvae fed with 45 and 50% protein diets. Carcass moisture and total lipids after 16 days of feeding did not differ significantly (P > 0.05), but body protein increased with increasing dietary protein. Body protein of the control larvae was similar to that of larvae given the 60% protein diet.     

Growth of Perca fluviatilis larvae fed with Artemia spp. nauplii and the effects of initial starvation

Experiments were performed to test the growth and survival of perch larvae fed with Artemia spp. nauplii and to determine the most advantageous time of first feeding. During a first experiment, perch larvae were divided into groups according to their hatching dates. Daily ingestion of Artemia spp. nauplii began significantly 2 days after mass larvae hatching. By day 7, the daily prey acceptance was over 75% among the separate larvae groups. During a second 14-day feeding experiment, larvae fed after a 2- or a 3-day delay showed the best growths: 12.5 mm and 13.7 mg. There was no significant difference (P > 0.05) among survival rates (85.3%) of perch larvae fed after a 1-, 2- or 3-day delay.     

Use of the rotifer, Brachionus calyciflorus Pallas, in freshwater ornamental fish larviculture

The Brachionus calyciflorus used in this study were produced by batchculture using Chlorella spp. as feed. Larviculture experiments in indoor10-l and 200-l tanks revealed that, compared with egg yolk, the rotifersused as starter food significantly improved the growth and survival of DwarfGourami larvae (Day 2–12). These beneficial effects also extended tothe subsequent Artemia feeding phase (Day 13–32), suggesting that thequality of starter food is crucial to later development. At metamorphosis,the overall survival rate of larvae fed on rotifers in indoor tanks(65.1–74.5%) was about four times of that obtained in extensiveculture in open ponds (17.5%). In Discus, larvae are dependent on thebody slime of their parent as a nutrient during the first two weeks ofexogenous feeding. Our observation demonstrated that Brown Discus larvaecould be raised in the absence of the parent fish by using rotifers asstarter food followed by Artemia nauplii. Their growth and survival ratewere comparable to those on parental feeding. The artificial feeding wouldeliminate the risk of larvae being eaten by the parent fish and shorten thebrooding interval of the spawners, thereby leading to higher yield of fry.This feeding protocol is less tedious and more practical for use incommercial farming of Discus than the existing strategies of smuggling thebatch of larvae to foster parents or feeding the larvae with egg food. Theuse of rotifers would enable freshwater larviculture to improve larvalperformance, increase yield, and facilitate breeding of new fish specieswith small larvae.     

Dietary neutral lipid level and source in Senegalese sole (Solea senegalensis) larvae: effect on growth, lipid metabolism and digestive capacity

Contrary to larval essential fatty acid (EFA) requirements, the effect of dietary neutral lipid supply has been little investigated in marine fish larvae. The present work investigates the effect of feeding Senegalese sole larvae on Artemia enriched with higher or lower doses of lipid emulsion. Two lipid sources - soybean oil and fish oil - were compared. From 16 days after hatching (DAH) onwards, larvae were fed one of four experimental treatments: Artemia enriched on a high or low dose of soybean oil emulsion (HS and LS) or Artemia enriched on a high or low dose of fish oil emulsion (HF and LF). In terms of growth, the dietary lipid level did not have a significant effect while the soybean oil treatments induced a lower growth than the fish oil-enriched Artemia. The fatty acid (FA) composition of the larvae closely reflected the dietary quantitative and qualitative FA profile. Only slight dietary effects were noted in the activity of trypsin, lipase and alkaline phosphatase. A higher amount of lipid droplets was noticeable in the posterior intestine epithelia and in the hepatocytes of larvae fed Artemia enriched with higher lipid doses, while LS-Artemia induced the lower lipid accumulation on the basal zone of the enterocytes, in accordance with the lowest total lipid level measured in this treatment. These results suggest an important effect of dietary total lipid level on lipid accumulation in the enterocytes and on FA absorption. At 33 DAH a tube feeding trial was conducted with 14C-labelled oleic acid (OA) or triolein (TRI), showing that the lower accumulation of lipid droplets in the larvae fed LS was associated with a significantly higher absorption and retention in the gut and body tissues of the TRI label. For OA no significant differences between treatments were found. TRI label was considerably more evacuated than OA, indicating that sole larvae may have a lower capacity to incorporate a triacylglycerol, which needs to be digested. Finally, OA appears to be preferentially utilized for energy production, accumulating more in larval tissues when absorbed in higher amounts.     

Comparison of some live organisms and artificial diet as feed for Asian catfish Clarias macrocephalus (Günther) larvae

Experiments were conducted to evaluate the efficacy of five live organisms (Artemia, Brachionus calyciflorus, Chironomus plumosus, Moina macrocopa and Tubifex sp.) and an artificial diet (40% protein) in the larval rearing of Asian catfish Clarias macrocephalus. The larvae were fed three times daily starting at the onset of exogenous feeding. Results showed that the catfish larvae utilized the live organisms more efficiently than the artificial diet. The Tubifex‐fed larvae consistently showed the highest growth rate. In trial 1, length increment (64.9 mm), weight gain (3192 mg) and specific growth rate (13.1%) after 8 weeks of feeding were significantly higher (P < 0.05) in catfish larvae given Tubifex than those in all other treatments. In trial 2, length increment after 4 weeks of feeding was highest in larvae fed Tubifex (22.9 mm) although it did not significantly differ from that of larvae given Moina (21.0 mm). However, weight gain of larvae fed Tubifex (253.0 mg) was significantly higher than that of larvae fed Moina (171.6 mg). The specific growth rate was highest for larvae fed Tubifex (15.0%) followed by larvae fed Artemia (14.5%), Moina (14.4%) and Chironomus (12.0%). Survival rates of the catfish larvae ranged from 9 to 39% after 8 weeks in trial 1 and from 26 to 83% after 4 weeks in trial 2. The present results suggest that Tubifex is an excellent food and a potential substitute for Artemia in the rearing of catfish larvae.     

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.     

Effect of feed on larvae of Macrobrachium malcolmsonii (H. Milne Edwards) reared in synthetic brackishwater

Freshwater prawn, Macrobrachium malcolmsonii, has potential for aquaculture. Larvae of M. malcolmsonii were reared in synthetic brackishwater using commercial salts. Live and artificial feeds were provided to larvae either individually or in combination. Survival was significantly higher when larvae were fed with live feed only. However, larvae fed with artificial feed showed significantly lower survival. Survival was significantly higher when Artemia combined together with other feeds. Despite its limitations, synthetic brackishwater can be used for freshwater prawn seed production.     

Effects of prey density and short term food deprivation on the growth and survival of American shad larvae

Growth and survival of 16-and 18-day-old American larvae ( Alosa sapidissima ) increased with prey density (0, 500, and 1000 Artemia l⁻¹), though differences were not always significant. Significant differences were not observed in growth parameters and survival for larvae fed 500 v . 1000 Artemia 1⁻¹ in laboratory experiments. Food deprivation for as little as 2 days had significant effects on survival but growth effects were not detectable until 4 days of starvation. These findings have application to the Susquehanna River where c . 11 million 2.5-week-old shad larvae are released annually as part of a basin wide effort to restore the species. Larvae released at upriver sites where food may be limiting would drift for 2–3 days to reach reservoirs with higher prey densities. Based on these laboratory findings, survival of shad may be reduced significantly if larvae do not feed prior to reaching reservoir environments.     

Growth and survival of tench larvae fed under different feeding strategies

Two feeding experiments were conducted to evaluate the growth and survival rates of tench Tinca tinca L. larvae when initially fed with a combination of three different brands of Artemia nauplii under two conditions: (A) in the laboratory and (B) on a commercial farm. At the same time, a protozoan culture of the freshwater ciliate Colpoda cucullus was additionally tested in one of the experiments to possibly enhance the initial hunting behaviour of the larvae. The larvae were fed every 4 h from the onset of exogenous feeding up to 14 days of age. Three types of commercial Artemia products, mainly differing in size and high unsaturated fatty acid (HUFA) content, were used. One group was fed with C. cucullus as a starter. The different combinations of Artemia nauplii were used to evaluate possible effects on larval growth. The final growth at 26.3 °C, expressed in length and weight, did not show significant differences, suggesting the use of the most economically feasible Artemia strain studied. The experiments confirmed that using smaller prey during the first 2 days of feeding increases their survival rate, although the mean final survival rate was high (89%). In the experiment carried out at the commercial fish farm facilities, experimental groups were also fed with Artemia nauplii, using the EG type either enriched or not enriched with HUFA. Again, one of the groups was offered the ciliate C. cucullus as initial feed. Final growth showed significant differences when using Colpoda culture as a starter feed, although this test resulted in the lowest survival rate (69%), indicating that further studies on the management of its culture should be undertaken to improve the applicability of the technique. The mean final survival rate was 83%.     

Critical involvement of dietary docosahexaenoic acid in the ontogeny of schooling behaviour in the yellowtail

To investigate involvement of the central nervous system in the ontogeny of behaviour, diets of differing quality were used to rear yellowtail Seriola quinqueradiata larvae and juveniles. Artemia nauplii enriched with oleic acid (OA), eicosapentaenoic acid (EPA), or two different concentration levels of docosahexaenoic acid (DHA) were fed to yellowtail larvae (L^T 7 mm; 13 days old) for 12 days, and their behavioural development was analysed together with growth, survival, activity and fatty acid composition. Yellowtail fed with DHA–enriched Artemia showed mutual attraction behaviour at 11 mm L^T, while those fed with OA– or EPA–enriched Artemia did not show this behaviour at the same size. While fish in the OA group showed poor growth, survival and activity index, fish in the EPA group were similar to the two DHA groups. In addition, most fish tested, including the OA group, showed clear optokinetic responses. Fatty acid composition of the diet was reflected in that of the fish body. Therefore, dietary DHA in the larval stage is considered to be essential for the development of schooling behaviour in the yellowtail.     

The occurrence of juvenile pigmentation abnormalities in plaice (Pleuronectes platessa) larvae fed on enriched and unenriched Artemia salina nauplii

The effect of diet on the frequency of malpigmentation was investigated in laboratory-reared plaice ( Pleuronectes platessa ) fed on either enriched or unenriched Artemia salina nauplii . The juveniles fed continuously on unenriched Artemia during their larval period showed 29.0% normal pigmentation whereas those fed solely on enriched Artemia , showed 63% normal pigmentation. The possibility of a critical period for pigment development was tested by changing the diet of larvae at different ages. Results suggested that a critical period is less important than the duration of time fed on a nutritionally complete diet.     

Development of sensory organs in larvae of African catfish Clarias gariepinus

African catfish Clarias gariepinus hatched with morphologically immature features; however, sensory organs developed rapidly with fish growth. Although the eyes of newly hatched larvae were immature without pigment, in 2 day‐old larvae, the retina of the eyes had already developed except for the rod cells. No free neuromasts were observed in newly hatched larvae. In 1 day‐old larvae, however, free neuromasts were observed on the head and trunk. Free neuromasts increased with larval growth. Newly hatched larvae had simple round‐shaped otic vesicles; however, all sensory epithelia of the inner ear were observed until the larvae were 3 days old. Two day‐old larvae swam horizontally, had sharp teeth, commenced ingesting rotifers and also artificial feed (small‐size pellets) under both light and dark conditions; by then the larvae already had many taste buds. Three day‐old larvae showed negative phototaxis and cannibalism by eating their conspecifics. Most of the free neuromasts observed in this study had the peculiar feature of many microvilli around the sensory cells on the apical surface. Detected free neuromasts as ordinary type lateral‐line organs were not observed in previous reports in teleosts. In 10 day‐old larvae, there were two lines of free neuromasts on the flank and lower edge of the trunk; presumptive canal neuromasts were oval shaped and had begun to sink under the skin. The direction of maximum sensitivity of the neuromasts was parallel with the longitudinal axis of their elliptical apical surface.     

Larval growth patterns in Cyprinus carpio and Clarias gariepinus with attention to the finfold

During the larval period, most teleost fishes undergo a dramatic change in body form. Most functional systems are incomplete at hatching. Rapid development of swimming, feeding and respiration systems are expected. In this study, growth patterns of morphological characteristics related to these three functions were studied in two species of Ostariophysian teleosts: African catfish Clarias gariepinus and common carp Cyprinus carpio . Special attention was paid to the larval finfold, which is a remarkably common feature of fish larvae. The results confirmed that larval growth shows different phases. Many morphological characters showed fast allometric growth in early larvae, followed by isometric growth after an inflexion point. In carp, all larval growth curves showed such inflexion points at a total length of about 7 mm while in Clarias such a coupling was not found. The inflexion points in carp occur at a stage during which the typical larval swimming style changes towards the adult swimming style.