Effects of bioflocs on water quality,and survival,growth and digestive enzyme activities of Litopenaeus vannamei (Boone) in zero‐water exchange culture tanks

A 30‐day experiment was performed to investigate the effects of bioflocs on water quality, and survival, growth and digestive enzyme activities of the white shrimp Litopenaeus vannamei. Altogether 28 shrimp (7.4 ± 0.1 g) were stocked in each 150 L tank. Two bioflocs treatments and one control were managed: ‘bioflocs 1’ and ‘bioflocs 2’ based on two different densities of the bioflocs, and clean water control without the bioflocs. Brown sugar was added to the bioflocs 1 and bioflocs 2 treatment tanks accounting for 28% and 80% of the shrimp feed respectively (corresponding to proximate C/N ratios of 10 and 14 in daily additions of organic matter respectively), so as to promote bioflocs production and approximately 14 mL L^?1 in treatment bioflocs 1 and 20 mL L^?1 in treatment bioflocs 2 were maintained from day 15. Monitoring of selected water quality parameters throughout the whole experiment period showed that all parameters remained within recommended levels for shrimp culture in the bioflocs treatments at zero‐water exchange, especially low total ammonia nitrogen and nitrite nitrogen levels. By the end of the experiment, shrimp survival rates were above 86%, with no significant differences (P > 0.05) among the three groups. Both weight gain rate and special growth rate tended to increase in the bioflocs treatments compared to those in the control. Meanwhile, the overall specific activities of protease, amylase, cellulase and lipase of the shrimp in the bioflocs treatments were all higher than those in the control; and for the specific activity of the same digestive enzyme, the differences between the bioflocs treatments and the control performed inconsistently among different organs: hepatopancreas, stomach and intestine. Present results suggest that the bioflocs can not only maintain favourable water quality conditions for shrimp culture and help shrimp grow well in zero‐water exchange culture systems, but may also have a positive effect on digestive enzyme activities of the shrimp.     

Prediction of culture performance of juvenile Litopenaeus vannamei by in vitro (pH-stat) degree of feed protein hydrolysis with species-specific enzymes

Rapid in vitro methods for measuring digestibility may be useful in analysing aqua feeds if the extent and limits of their application are clearly defined. The pH‐stat protein digestibility routine with shrimp hepatopancreas enzymes was previously related to apparent protein digestibility with juvenile Litopenaeus vannamei fed diets containing different protein ingredients. The potential of the method to predict culture performance of shrimp fed six commercial feeds (T3, T4, T5, T6, T7 and T8) with 350 g kg^?1 declared crude‐protein content was assessed. The consistency of results obtained using hepatopancreas enzyme extracts from either pond or clear water‐raised shrimp was further verified in terms of reproducibility and possible diet history effects upon in vitro outputs. Shrimps were previously acclimated and then maintained over 56 days (initial mean weight 3.28 g) on each diet in 500‐L tanks at 114 ind m^?2, clear water closed system with continuous renewal and mechanical filtering (50 μm), with four replicates per treatment. Feeds were offered four times daily (six days a week) delivered in trays at feeding rates ranging from 4.0% to 7.0% of stocked shrimp biomass. Feed was accessible to shrimp 4 h daily for 1‐h feeding period after which uneaten feed was recovered. Growth and survival were determined every 14 days from a sample of 16 individuals per tank. Water quality was monitored daily (pH, temperature and salinity) and managed by water back flushing filter cleaning every 7–10 days. Feeds were analysed for crude protein, gross energy, amino acids and pepsin digestibility. In vitro pH‐stat degree of protein hydrolysis (DH%) was determined for each feed using hepatopancreas enzyme extracts from experimental (clear water) or pond‐raised shrimp. Feeds resulted in significant differences in shrimp performance (P < 0.05) as seen by the differences in growth rates (0.56–0.98 g week^?1), final weight and feed conversion ratio (FCR). Shrimp performance and in vitro DH% with pond‐raised shrimp enzymes showed significant correlation (P < 0.05) for yield (R² = 0.72), growth rates (R² = 0.72–0.80) and FCR (R² = ?0.67). Other feed attributes (protein : energy ratio, amino acids, true protein, non‐protein nitrogen contents and in vitro pepsin digestibility) showed none or limited correlation with shrimp culture performance. Additional correlations were found between growth rates and methionine (R² = 0.73), FCR and histidine (R² = ?0.60), and DH% and methionine or methionine+cystine feed contents (R² = 0.67–0.92). pH‐stat assays with shrimp enzymes generated reproducible DH% results with either pond (CV ≤ 6.5%) or clear water (CV ≤ 8.5%) hepatopancreas enzyme sources. Moreover, correlations between shrimp growth rates and feed DH% were significant regardless of the enzyme origin (pond or clear water‐raised shrimp) and showed consistent R² values. Results suggest the feasibility of using standardized hepatopancreas enzyme extracts for in vitro protein digestibility.     

Optimum dietary protein‐to‐energy ratio for juvenile whiteleg shrimp,Litopenaeus vannamei,reared in a biofloc system

An 8‐week feeding trial was conducted to evaluate the optimum dietary protein‐to‐energy (P/E) ratio in juvenile whiteleg shrimp, Litopenaeus vannamei. Six diets were formulated with two protein levels (30% and 35%) and three digestible energy levels (16, 17.5 and 19 kJ/g diet) at each protein level (₃₀P₁₆, ₃₀P_17.5, ₃₀P₁₉, ₃₅P₁₆, ₃₅P_17.5 and ₃₅P₁₉). Fifty shrimp averaging 0.97 ± 0.03g (Mean ± SD) were randomly distributed in biofloc tanks and fed one of the experimental diets. Weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of shrimp fed the ₃₅P_17.5 diet were significantly higher than those of shrimp fed ₃₀P₁₆, ₃₀P_17.5 and ₃₀P₁₉ diets (p < .05). Results for non‐specific immune responses showed that diet ₃₅P_17.5 caused higher lysozyme activity in shrimp comparing to lower protein diets. Thiobarbituric acid reactive substances (TBARS) of plasma were lower for shrimp fed on diets consisting of higher protein and energy levels than shrimp fed on the ₃₀P₁₉ diet. Analyses of digestive enzyme activities showed higher trypsin activities for shrimp fed on ₃₅P_17.5 and ₃₅P₁₉ diets comparing to ₃₀P₁₆ and ₃₀P_17.5 diets. Also, hepatopancreatic lipase activity of shrimp fed ₃₅P₁₆, ₃₅P_17.5 and ₃₅P₁₉ diets were significantly higher than those of shrimp fed the other diets. In conclusion, based on the results for growth performance, biochemical parameters, immune responses, oxidative stress and enzyme activities, 35% protein and 17.5 kJ/g digestible energy (₃₅P_17.5) could be considered as the optimum protein‐to‐energy ratio in the diet of juvenile whiteleg shrimp reared in a biofloc system.     

Compensatory growth and digestive enzyme activity of Litopenaeus vannamei submitted to feeding restriction in a biofloc system

Feeding restriction is a strategy in shrimp farming management that may promote compensatory growth after feeding is re‐established. This study aims to evaluate the effects of two feeding restriction regimens on the compensatory growth and digestive enzymes activity of Litopenaeus vannamei reared in biofloc system. Juvenile shrimp (0.46 ± 0.18 g) were stocked (320 individuals/m³) in 310 L tanks. The experiment comprised two phases: (a) Feeding Restriction (30 days) when shrimp were submitted to three feeding regimes, Control (fed daily), R1F1 (repetitively fasted one day and fed one day) and R2F1 (repetitively fasted 2 days and fed 1 day); and (b) Refeeding (28 days) when shrimp were fed daily. In the restriction phase, shrimp growth and digestive enzyme activities were reduced in R2F1 and R1F1. However, during the refeeding phase, enzyme activities and feed conversion improve significantly in R2F1 and R1F1. Control group attained higher final weight, but its final biomass was similar to R1F1. Litopenaeus vannamei exhibited partial compensatory growth, probably due to improved feed conversion efficiency driven by increased enzyme activity. It is possible to reduce feeding by 50% (R1F1) in biofloc systems for 28 days, without compromising the biomass produced at the end of a 30‐day refeeding period.     

Characterization of bacterial community in intestinal and rearing water of Penaeus monodon differing growth performances in outdoor and indoor ponds

Penaeus monodon provides a high‐quality protein source for humanity, and pond cultured shrimp often presents asynchronous growth. Microbial communities are important for the digestion and immunity of shrimp. Therefore, in this study, we investigated the bacterial characteristics of the intestine and rearing water of asynchronously growing P. monodon that were cultured in outdoor and indoor pond respectively. The results showed that the bacterial community of the rearing water was more complex than that of the intestine; the fast‐growing shrimp in the indoor pond had higher intestinal bacterial diversity. Besides, the dominant bacterial composition of the water was more complex than that of the intestinal. Specifically, the abundance of Proteobacteria in the intestine was consistent with the growth performance of shrimp in the outdoor pond, which was exactly the opposite in the indoor pond. At the genus level, two cyanobacteria, Limnothrix and Cyanobium PCC‐6307, were dominant in the indoor and outdoor water respectively. In the outdoor pond, Bacillus was dominant in the slow‐growing shrimp intestines, while Vibrio was dominant in the fast‐growing shrimp. The intestinal microbes of the fast‐growing shrimp had higher proteasome metabolic capacity. These results can provide new insights into microbiome characteristics involved in the asynchronous growth of shrimp.     

Growth,digestive enzymes activities,serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (Oreochromis niloticus) reared at different stocking densities in in‐pond raceway recirculating culture system

The feeding trial was conducted in 80 days to assess the effects of stoking densities on growth, digestive enzymes activities, serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus) reared in in‐pond raceway recirculating culture system (IPRS). Fish (initial body weight: 6.25 ± 0.32g ) were randomly allotted to six in‐pond raceways (22 × 5 × 2.5 m) stocked at three different stocking densities: low stocking density (LSD, 0.28 kg/m³), medium stocking density (MSD, 0.57kg /m³) and high stocking density (HSD, 0.85 kg /m³). The results indicated that no significant differences were observed in final body weight, weight gain and specific growth rate of GIFT reared at different stocking densities on day 20 (p > 0.05). Fish reared in the HSD group showed poor growth than those reared in the LSD and MSD groups on day 50, but fish reared in the MSD and HSD groups showed poor growth than those reared in the LSD group on day 80. There were no significant differences found in digestive enzyme activities, serum cortisol, lysozyme and superoxide dismutase (SOD) content, hepatic catalase (CAT), total SOD, total antioxidant capacity (T‐AOC) activities and malondialdehyde (MDA) content among fish reared at different densities treatments (p > 0.05). Fish reared in the HSD group exhibited significant higher red blood cell number, haematocrit and glucose (GLU) contents on day 80 (p < 0.05). In brief, under this trial conditions, high stocking densities (0.57 kg/m³) resulted in decrease in growth, and GIFT might have an adaptation capability to crowding stress without a change in antioxidant activity, some physiological and immune parameters.     

Carotenoids and retinal levels in captive and wild shrimp, Litopenaeus vannamei

In farm‐raised marine organisms, the interactions and functions of carotenoid and retinoid micronutrients as free radical scavengers during specific physiological processes, such as gonadic maturation, are not known. Captive and wild female white shrimp, Litopenaeus vannamei, were sampled at two maturation stages: II and IV. Total carotenoids, a carotenoid profile, and vitamin A from the digestive gland and ovary were determined. Superoxide dismutase (SOD) activity was determined in hemolymph. The carotenoid concentration and range of activity were significantly higher (P < 0.05) in wild than in captive shrimp, particularly at maturation stage IV. Activity of SOD in hemolymph of captive shrimp at both stages of maturation was significantly greater (P < 0.05) than that of wild organisms. In sexually exhausted, level IV captive shrimp, low carotenoid concentrations, mainly in digestive gland and ovary, reflected scavenger action insufficient to neutralize oxidative stress processes, as suggested by SOD activity. Carotenoids are important nutrients associated with the reproductive capacity of shrimp.     

Effects of different carbon sources addition on nutrition composition and extracellular enzymes activity of bioflocs,and digestive enzymes activity and growth performance of Litopenaeus vannamei in zero‐exchange culture tanks

A 35‐day feeding experiment was conducted to investigate the effects of different carbon sources addition on nutritional composition and extracellular enzymes activity of bioflocs, and digestive enzymes activity and growth performance of Litopenaeus vannamei juveniles (average 5.52 ± 0.21 g) in zero‐water exchange culture tanks. Molasses, corn flour and wheat bran were used as carbon sources and added into the tanks to promote the development of bioflocs during the experiment. During the entire experiment, good water quality and biofloc development were achieved under the addition of different carbon sources. At the end of the experiment, the proximate composition and extracellular enzymes activities of the collected bioflocs from seven biofloc groups were influenced by the addition of the different carbon sources. Meanwhile, the specific activities of protease, amylase, lipase and cellulase in the hepatopancreas, stomach and intestine of the shrimp showed differences among the seven biofloc groups, and most of them were significantly higher than those obtained in the control group (P < 0.05). There were differences in the performance (growth and FCR) of the shrimp among the seven biofloc groups, and all of them were significantly better than those obtained in the control group (P < 0.05). Based on the results of this study, 60% molasses + 20% corn flour + 20% wheat bran could be an appropriate formula of the addition of carbon sources for intensive culture of L. vannamei (mainly in terms of growth and FCR) in zero‐water exchange culture tanks.     

Ontogenic development of enzymatic activity and digestive system in Jullien's golden carp (Probarbus jullieni Sauvage, 1880)

Ontogenic development of the main enzymes and histological structure of digestive organs were studied in Jullien's golden carp (Probarbus jullieni) from hatching until 50 days after hatching (DAH). The larval fish were produced by artificial insemination and fed only Moina sp. till end of experiment. Body weight (mg) and total length (cm) of Jullien's golden carp increased exponentially and linearly. The results indicate the fish weight grew fast with increasing rate, while length increased at a constant rate over the studied period. Up‐regulation of acid protease was observed in newly hatched larvae and the specific activity gradually decreased with time. Trypsin specific activity was relatively stable within the first 35 DAH, while fluctuations in chymotrypsin were observed. Among these three proteolytic enzymes, acid proteases exihibited relatively high specific activity in newly hatched larvae, suggesting a role in yolk protein degradation. Alkaline proteases became more prominent with age and correlated with an abrupt decrease in acid proteases. Increased lipase‐specific activity appeared within 3 DAH and then gradually decreased with time, indicating the capacity to digest yolk lipid reserve. Amylase and cellulase‐specific activities changed in a similar manner, and the sensitivity to time was higher in amylase than in cellulase. The digestive organs and accessory organs developed around 3–5 DAH. However, intestinal histology was almost fully developed around 18 DAH. These findings should be useful for deciding the preferred timing for weaning, as well as on developing artificial diets referenced to the physiological changes of digestive enzymes.     

Enhancement of innate immune system,survival and yield in Penaeus monodon reared in ponds using Streptococcus phocae PI80

The objective of this study was to evaluate the effect of dietary and water supplementation of probiotic Streptococcus phocae PI80 on growth, immune response and feed utilization of tiger shrimp Penaeus monodon in earthen ponds. The probiotic bacterium S. phocae PI80 was cultured in large fermenter (50 L) by adding additional carbon source in the form of molasses and glucose along with yeast extract as nitrogen source to enrich S. phocae PI80 biomass. This enriched S. phocae PI80 was administered to shrimp in feed (6.5 × 10¹³ bacterial cells mL^?1) as well as in pond water (5 L/pond). Shrimp growth performance was significantly improved (P < 0.05) in 120 days culture when the average body weight of treated molasses + yeast extract (MY) (28.41 ± 0.874 g), glucose + yeast extract (GY) (27.013 ± 0.698 g) was significantly higher than control (23.63 ± 0.684 g). Food conversion ratio FCR was also found to be reduced significantly in ponds treated with probiotics when compared with control pond (1.89 ± 0.09). Vibrio and luminescent bacteria were found to be lower in the treatment receiving MY group, and we hypothesize that this may lead to greater shrimp survival. Furthermore, fermentation product of S. phocae PI80 added to pond water and feed additives enhanced the shrimp immune system. The results indicated that total haemocytes count (THC), phenoloxidase (PO) activity, NBT reductase assay and phagocytic activity significantly increased in shrimps treated with S. phocae PI80. Our study demonstrates that administration of S. phocae PI80 in the water and feed at 6.5 × 10¹³ colony‐forming units (CFU) mL^?1 bacterial cells induce immune modulation and enhances the immune ability of P. monodon in pond‐reared shrimp and increased the shrimp production.     

A dietary modification approach to improve the osmoregulatory capacity of Litopenaeus vannamei cultured in the Arizona desert

A modified diet was formulated for Arizona inland shrimp farming and tested as a method for reducing moult‐associated mortalities presumed due to trace mineral deficiencies. The experimental diet was supplemented with additional dietary magnesium, potassium, phospholipids and cholesterol to a commercial shrimp feed (Rangen 45/10, which was also used as the control diet). The modified diet was tested at Arizona Mariculture Associates (AMA), while the control diet was used at a nearby inland shrimp farm, Desert Sweet Shrimp Farm (DSSF). Both feeds were used throughout the culture season of 2001. Earthen pond‐reared Litopenaeus vannamei at intermoult stages (C‐D₀) and ranging from 7 to 30 g were sampled at intervals for determination of haemolymph osmolality (HO). Results showed that the modified diet had not only resulted in larger size shrimp at harvest, but also improved osmoregulatory capacity (OC). HO of DSSF shrimp decreased as shrimp grew bigger, whereas HO of AMA shrimp was maintained at a stable level, or showed a slightly positive linear relationship with weight. The hyper‐OC of shrimp from AMA (462 mOsm kg^?1) was greater than that from DSSF (398 mOsm kg^?1). Shrimp at AMA fed the experimental diet presented no mass moult‐associated mortalities. To further investigate the iso‐osmotic point of shrimp reared in AMA, a group of six salinity gradients were designed by mixing oceanic salts into the well water to form 5, 8.5, 11.4, 14.4, 17.8, 20.7 p.p.t. medium. HO of subadult shrimp (25 g in average) were then evaluated 48 h after they had been transferred from 5 p.p.t. pond water to the medium. Shrimp HO increased with external salinity, and a plateau formed as salinity reached at 11.4 p.p.t. and higher. The iso‐osmotic point of shrimp was estimated to be 695.5 mOsm kg^?1, equivalent to 26.1 p.p.t. in AMA well water.     

Digestive enzyme activity at different developmental stages of blackspot seabream, Pagellus bogaraveo (Brunnich 1768)

Blackspot seabream, Pagellus bogaraveo (Brunnich), has been identified as a potential species to diversify European aquaculture production. Although rearing aspects have been widely investigated, little information exists on the nutritional requirements for this species. The aim of this study was to build up information on the activity of digestive enzymes at certain developmental stages of blackspot seabream in order to understand the nutritional needs of larvae and post larvae. Fish larvae were reared from hatching to 55 days after hatching (dah), and the feeding plan consisted in rotifers (5–35 dah), Artemia naupli (30–35 dah) metanaupli (35–45) and Gemma microdiet (45–55 dah). At 7, 11, 21, 45 and 55 days after hatching (dah), pooled samples of fish larvae were collected for analysis of trypsin, amylase, lipase, alkaline phosphatase and leucine–alanine peptidase activity. Up to 21 dah, the whole larvae body was used for enzymatic analysis, whereas in older larvae only the dissected abdominal cavity was used. Blackspot seabream body dry weight growth was exponential, increasing from 60 μg at 5 dah to 30±9.7 mg at 55 dah. Amylase specific activity decreased significantly during development, exhibiting at 11 dah (0.6 U mg^?1 protein) an average value 2.7 times lower than at 7 dah, and remaining stable between 45 and 55 dah (0.7 U mg protein^?1). Trypsin specific activity remained constant until 21 dah (between 38 and 44 mU mg protein^?1), which could be related to the larvae feeding regime. At later stages of development, lipase‐specific activity exhibited a significant increase (P<0.05), being three times higher at 55 dah (8 U mg protein^?1) than at 45 dah. The total activity of the studied digestive enzymes increased significantly during larval development (until 21 dah), whereas afterwards only lipase and leucine–alanine peptidase increased significantly between 45 and 55 dah. The pattern of digestive enzymes activity was related to organogenesis and the type of food used at different developmental stages.     

Influence of light intensity on biofilm formation and the performance of pink shrimp Farfantepenaeus paulensis juveniles reared in cages

A reduction in light intensity may increase shrimp activity, although it may also negatively affect the development of photoautotrophic organisms present in biofilm, an important natural food source for shrimp. This experiment evaluated the influence of light intensity on biofilm development and on the growth of cultured Farfantepenaeus paulensis juveniles. Six cages were deployed in a shrimp culture pond and stocked with 60 juveniles (0.72 ± 0.03 g). Three cages were randomly chosen and covered with five layers of polyamide net to reduce light incidence (shaded treatment), while the other three cages were not covered (control treatment). Biofilm chlorophyll a and microorganism abundance, as well as shrimp growth, were monitored during the experiment. Chlorophyll a concentration and the abundance of bacteria and flagellates were significantly lower in the shaded treatment (P<0.05). After 75 rearing days, shrimp stocked in control treatment achieved significantly higher (5.98 g) (P<0.05) mean weight than shrimp reared in shaded treatment cages (5.13 g). Similarly, the biomass produced was also significantly higher (P<0.05) in the control treatment (322.92 g) than in the shaded treatment (287.31 g). The results of this study demonstrate that light intensity has a huge influence on shrimp performance mainly due to the increase in natural food availability.     

Effects of dietary heat‐killed Lactobacillus plantarum L‐137 (HK L‐137) on the growth performance,digestive enzymes and selected non‐specific immune responses in sea cucumber,Apostichopus japonicus Selenka

A feeding trial was conducted to evaluate the efficacy of dietary heat‐killed Lactobacillus plantarum L‐137 (HK L‐137) on growth performance, digestive, non‐specific immune and phagocytosis of sea cucumber, Apostichopus japonicus. Sea cucumbers (initial body weight 1.35 ± 0.04 g) were fed diets supplemented with five levels of HK L‐137 (0, 0.005, 0.025, 0.05 and 0.25 g HK L‐137 kg^?1 diets) for 60 days. Results indicated sea cucumbers fed with diets containing 0.05 and 0.25 g HK L‐137 kg^?1 diets showed significantly (P < 0.05) higher body weight gain and specific growth rate than other groups. Sea cucumbers fed with diets containing 0.05 and 0.25 g HK L‐137 kg^?1 diets showed significantly (P < 0.05) higher protease activity than control group. Higher amylase, lysozyme and phagocytic activities were found in 0.25 g HK L‐137 kg^?1 diet group. Higher superoxide dismutase enzyme and alkaline phosphatase activity was found in 0.05 g HK L‐137 kg^?1. While no significant differences (P > 0.05) were found in acid phosphatase activity. These results suggested that dietary supplementation of 0.05 g HK L‐137 kg^?1 diets would have benefit on growth, digestive enzymes and several non‐specific immune parameters of sea cucumber.     

Effects of biological water purification grid on microbial community of culture environment and intestine of the shrimp Litopenaeus vannamei

Biological water purification grid (BWPG), a type of biofilm, could increase aquaculture production by improving the growth of shrimp and culture environment. In this study, the microbial community composition and diversity of water, sediment and shrimp intestine were analysed using the Illumina Miseq high‐throughput sequencing technique. Installation of BWPG did not only increase the dissolved oxygen, pH and decreased inorganic nutrients, but also increased shrimp body length by 5.39% and weight by 16.35%. Furthermore, it was found that the microbial community diversity of water and shrimp intestine in test pond with BWPG was higher than that of control pond without BWPG. Cyanobacteria, Bacillus and Lactococcus were enriched in the test pond with BWPG. However, Rhodobacter was mainly identified in the test pond. It thus seems to suggest that the application of BWPG in shrimp culture pond enhanced the microbial species richness, types of species and proportion of beneficial bacteria in culture environment as well as shrimp intestine. The results from this study will therefore provide some scientific basis for the improvement and development of shrimp aquaculture.     

不同饵料对海蜇幼体生长、消化酶、抗氧化和免疫酶活力的影响

本研究旨在探讨不同饵料对海蜇(Rhopilema esculentum)幼体生长、消化酶、抗氧化酶和非特异性免疫酶活力的影响。实验设置4个饵料组:小球藻组、虾片(对虾开口饵料)组、卤虫无节幼体组和混合组(卤虫无节幼体和虾片等比例混合),养殖实验持续进行30 d。结果显示:混合组和卤虫无节幼体组海蜇的增重率(WGR)和特定生长率(SGR)都显著高于其他各组(P<0.05);混合组海蜇胃丝的蛋白酶活力显著高于小球藻组和虾片组(P<0.05);虾片组海蜇口腕的淀粉酶活力显著高于其他各组(P<0.05);各饵料实验组的脂肪酶活力均显著高于初始组(P<0.05);在海蜇的体腔液中,混合组和卤虫无节幼体组的超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、总抗氧化能力(T-AOC)和溶菌酶(LZM)活力均显著高于其他各组(P<0.05)。研究表明,混合组和卤虫无节幼体组可以显著促进海蜇的生长,增强海蜇的抗氧化能力和免疫酶活力。     

Influence of dietary protein on digestive enzyme activity, growth and tail muscle composition in redclaw crayfish, Cherax quadricarinatus (von Martens)

This study was conducted to evaluate the effects of dietary protein on digestive enzyme profiles, growth and tail muscle composition in the freshwater redclaw crayfish, Cherax quadricarinatus. Crayfish were fed five diets that consisted of a commercial crayfish pellet and experimental diets containing 13%, 18%, 25% or 32% crude protein (CP), for a period of 12 weeks. Analysis of digestive enzyme profiles from the midgut gland (MG) revealed a positive correlation between protease, amylase and cellulase activities and dietary protein level. For all treatments, carbohydrase activity levels (cellulase and amylase) were significantly higher than those detected for protease. As dietary protein was elevated, there was a general increase in specific growth rate (SGR), with the highest SGR (0.58 ± 0.06) values observed in crayfish fed the diet containing 25% CP. Feed conversion ratio (FCR) ranged between 5.84 and 6.97 and did not differ significantly among the treatment groups including the reference diet, with the exception of the low‐protein diet (13% CP) which showed an FCR of 9.31. Finally, regression analysis revealed a strong positive correlation between the level of dietary protein and CP content in the tail muscle (P=0.004; r²=0.99).     

Digestive enzyme activity and food ingesta in juvenile shrimp Litopenaeus vannamei (Boone, 1931) as a function of body weight

A study was conducted to evaluate variations of digestive enzyme activities in Litopenaeus vannamei (Boone) reared in commercial ponds under semi‐intensive conditions. Shrimp were collected at each body weight increase of 2 g. As the shrimp grew (2–12 g), significant increases in the activities of lipase and chymotrypsin were observed. The total protease activity decreased from 6 g onwards. Trypsin activity showed a peak at 6 g and amylase activity increased two‐fold after 2 g. Additionally, the stomach contents were analysed microscopically for shrimp between 2 and 10 g. Plant matter contributed above 30% of the total stomach content in 6‐, 8‐ and 10‐g shrimp. Detritus represented 58% and 62% of the total stomach content in 2‐ and 4‐g shrimp, respectively, decreasing to 33–43% at greater shrimp weights. Artificial feed showed a maximum contribution of 20% in 6‐g shrimp. The present results show changes in the enzyme activity after the shrimp reach 6 g in body weight, evidenced by a decrease in total protease and an increase in lipase and amylase activities. The amylase/protease ratio was 2.6 in 2‐g shrimp and increased steadily to 9.6 in 12‐g shrimp. These findings suggest an adaptation of the enzymatic activity to diets with lower protein content as body weight increases, and may be related to the variation of the different items found in the stomach.     

Effects of genetic strain and holding facility on the characteristics of alkaline phosphatase and brush border enzymes in silver perch (Bidyanus bidyanus)

The activity of the enzymes located in the digestive tract (pyloric caeca and intestine) in two strains and F₁ crosses of the Australian freshwater fish silver perch [Murray River (M) and Cataract Dam (C)] was evaluated. The effect of the fish holding system (cages or ponds) on the activity of alkaline phosphatase (AP) and the brush border enzymes: maltase, leucine amino peptidase (LAP) and γ‐glutamyl transferase (γ‐GT) was examined. The enzymatic activity was tested in three intestinal sections: the pyloric caeca, upper and lower intestine. All the tested enzyme activities were influenced by an interaction between the intestinal section and the strain or cross of silver perch. For fish maintained in ponds, there were two distinct enzymatic activity patterns, one for the pure strains (C × C and M × M) and one for the crosses (C × M and M × C). Significantly higher (P<0.05) enzymatic activities of the crosses compared with the pure strains were particularly noticeable in the pyloric caeca. In fish held in cages, there was a significantly higher (P<0.05) enzymatic activity in the pyloric caeca of the C × C strain. The total enzymatic activities in the fish reared in the ponds were significantly higher (P<0.05) than those in the fish held in cages. The results of the present investigation confirm that the different genetic background of the silver perch in the Murray River and in the Cataract Dam influences the activity of the brush border digestive enzymes. This activity also varies between maintenance systems.     

Effects of soluble dietary cellulose on specific growth rate,survival and digestive enzyme activities in three freshwater crayfish (Cherax) species

The current study evaluated the effect of soluble dietary cellulose on growth, survival and digestive enzyme activity in three endemic, Australian freshwater crayfish species (redclaw: Cherax quadricarinatus, marron: C. tenuimanus, yabby: C. destructor). Separate individual feeding trials were conducted for late‐stage juveniles from each species in an automated recirculating freshwater, culture system. Animals were fed either a test diet (TD) that contained 20% soluble cellulose or a reference diet (RD) substituted with the same amount of corn starch, over a 12‐week period. Redclaw fed with RD showed significantly higher (P < 0.05) specific growth rates (SGR) compared with animals fed the TD, while SGR of marron and yabby fed the two diets were not significantly different. Expressed cellulase activity levels in redclaw were not significantly different between diets. Marron and yabby showed significantly higher cellulase activity when fed the RD (P < 0.05). Amylase and protease activity in all three species were significantly higher in the animals fed with RD (P < 0.05). These results indicate that test animals of all three species appear to utilize starch more efficiently than soluble dietary cellulose in their diet. The inclusion of 20% soluble cellulose in diets did not appear, however, to have a significant negative effect on growth rates.