Diet shift of larval and juvenile landlocked Ryukyu-ayu <Emphasis Type="Italic">Plecoglossus altivelis ryukyuensis</Emphasis> in the Fukuji Reservoir,Okinawa Island,Japan

ABSTRACT:   The diet shift of larval and juvenile Ryukyu-ayu Plecoglossus altivelis ryukyuensis was investigated for the landlocked population stocked in the Fukuji Reservoir, Okinawa Island. Gut contents of 274 specimens (5.1–31.4 mm in body length) including 31 yolk-sac larvae (5.7–8.0 mm) were examined. The diet of larval and juvenile landlocked P. a. ryukyuensis was mainly composed of zooplankton such as dinoflagellates, rotifers, copepods, and cladocerans. Feeding incidence was 48% in total and it gradually increased with growth. Diet analysis clearly demonstrated a diet shift during the larval and juvenile periods. For yolk-sac larvae and 5.0–19.9 mm fish, the diet was dominated by dinoflagellates Gymnodinium sp., and Peridinium sp., both numerically and by frequency, followed by rotifers that mainly consisted of Polyarthra spp. Diet breadth (Levin's standardized index B_A) diversified with growth, and feeding on copepods and cladocerans gradually increased in 10.0–14.9 mm fish. Diet overlap (Morisita's index: C) showed that diet drastically changed in 20.0–24.9 mm fish with a specialization on cladocerans Bosminopsis deitersi and Diaphanosoma brachyurum . This diet shift probably corresponded with an increase of feeding ability resulting from an enlargement of the mouth, increased swimming ability, and the development of sense organs.     

Dietary carbohydrate/lipid ratios and nutritional condition in juvenile southern rock lobster, Jasus edwardsii

The availability of formulated diets is considered economically imperative if rock lobster aquaculture, based on the collection and ongrowing of puerulus, is to progress. Central to the development of diets is an understanding of the nutritional requirements of the species. This study determined the effect of different dietary carbohydrate/lipid ratios (17:1, 5:1, 2:1, 0.8:1) on the growth and nutritional condition of juvenile southern rock lobsters, Jasus edwardsii, by measuring standard growth parameters, proximate composition of the whole body and digestive gland, and from a histological investigation of the digestive gland. Four replicate groups of eight lobsters (initial weight 5.08±0.98 g (mean±S.D.)) per diet treatment were held in 50 l tanks, in a recirculating system at 18 °C for 84 days. Maximum growth and the highest levels of lipid and dry matter in digestive glands and whole bodies was found in lobsters fed a diet containing 27% carbohydrate and 13.5% lipid (2:1 ratio) suggesting that of the four experimental diets, this diet provided the best balance of lipid and carbohydrate. Digestive gland histology supported this conclusion and lobsters fed low carbohydrate, high lipid diets were in the best nutritional condition, with high lipid accumulation, and structurally sound epithelial cells. Digestive gland epithelial cells of lobsters fed the high carbohydrate, low lipid diets were compressed, of inconsistent shape and size, with low lipid accumulation. Histology is therefore seen as a feasible method, in addition to growth and proximate composition data, to further examine the effect of diets in nutritional studies of crustaceans.     

Effects of weaning age and diets on ontogeny of digestive activities and structures of pikeperch (<Emphasis Type="Italic">Sander lucioperca</Emphasis>) larvae

Growth and ontogeny of digestive function were studied in pikeperch (Sander lucioperca) larvae weaned on artificial food at different ages. Three weaning treatments initiated respectively on day 9 (W9), day 15 (W15) or day 21 (W21) post-hatching (p.h.) were compared with a control group, fed Artemia nauplii from first feeding until the end of the rearing trial on day 36 p.h. The digestive enzyme activities and the ontogeny of digestive structures were investigated using enzymatic assays and histological methods. Growth of pikeperch larvae was significantly affected by precocious weaning. Pancreatic (trypsin and amylase) and intestinal (leucine-alanine peptidase, leucine aminopeptidase N and alkaline phosphatase) enzyme activities were detected from hatching onwards, increased at the moment of first feeding and then decreased. Pepsin secretion occurred at day 29 p. h. only, concurrently with the stomach development and differentiation of gastric glands. In the early weaning group (W9) the maturation process of intestinal enterocytes seems to be impaired and/or delayed and several signs of malnutrition were recorded. Except for alkaline phosphatase activity, no differences in enzyme activities and development of digestive structures were observed among the control, W21, and W15 groups. Moreover, at the end of the experiment, no differences in proteolytic activities were observed among larvae from the different treatments, indicating that, in surviving individuals, the digestive structures were properly developed and the larvae had acquired an adult mode of digestion. Based on the artificial diet used, our results suggested that pikeperch larvae can be weaned from day 15 p.h. without significant adverse effect on digestive capacities (except for alkaline phosphatase) or development of digestive tract, while earlier weaning impaired the onset of the maturation processes of the digestive system, both in terms of morphological structures and enzymatic activities.     

Effective use of glucose rather than starch in formulated semimoist diets of common octopus (Octopus vulgaris)

The aim of the present work was to test the capacity of Octopus vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg^?1 water, 200 g kg^?1 gelatine, 100 g kg^?1 egg yolk powder, 50 g kg^?1 freeze‐dried Sardinella aurita and 150 g kg^?1 freeze‐dried Todarodes sagittatus) and two obtained by substituting 50 g kg^?1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best‐accepted diet was STA50 (SFR 1.26%BW day^?1) although there were no significant differences in the growth rates obtained with the three diets: 10.12 g day^?1, 9.37 g day^?1 and 11.22 g day^?1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 71.88% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all the three diets (96–98% for proteins and 85–94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.     

Effects of lysine and methionine supplementation on growth,body composition and digestive function of grass carp (Ctenopharyngodon idella) fed plant protein diets using high‐level canola meal

A 76‐day feeding trial was carried out to evaluate the effects of Lysine and Methionine supplementation on growth and digestive capacity of grass carp (Ctenopharyngodon idella) fed plant protein diets using high‐level canola meal (CM). Fish with initial average weight 103.9 ± 0.6 g were fed three extruded diets. Fish meal (FM) diet was formulated as the normal control with 40 g kg^?1 FM and 300 g kg^?1 CM; CM diet was prepared by replacing all FM with CM (total 340 g kg^?1) without Lys or Met supplementation; CM supplement (CMS) diet was similar to CM diet but was supplemented with essential amino acids (EAA) to ensure the levels of Lys and Met similar to those in the FM diet. Feed intake, feed efficiency and specific growth rate of the grass carp fed CMS and FM diets were similar (P > 0.05), but higher than those of the grass carp fed CM diet (P < 0.05). The hepatosomatic index, relative gut length, intestosomatic index and intestinal folds height were significantly improved in fish fed FM and CMS diets as compared to CM diet (P < 0.05). Lower activities of trypsin, lipase and amylase in hepatopancreas were observed in fish fed CM diet (P < 0.05). Three hundred and forty gram per kilogram CM without Lys or Met supplementation significantly decreased trypsin, lipase and amylase mRNA levels in hepatopancreas (P < 0.05). These results indicated that the high supply of CM (340 g kg^?1) in plant protein (200 g kg^?1 soybean meal and 100 g kg^?1 cottonseed meal) diets decreased digestive ability through decreasing digestive enzyme activities and enzyme gene's expressions of grass carp, and these side effects can be reversed by supplementing Lys and Met. Therefore, CM could be high level used in a plant protein blend‐based extruded diet for grass carp as long as EAA were supplemented.     

东海北部近海棘头梅童鱼食物组成的季节变化及随发育的变化

根据2006年7月～2008年12月采集于东海北部近海的棘头梅童鱼(Collichthys lucidus)样品,共测定体长在23～157 mm范围内的棘头梅童鱼474 ind,应用卡方检验和聚类分析等方法,对棘头梅童鱼食物组成的季节变化及随个体发育的变化进行了分析。结果显示:东海北部近海棘头梅童鱼的食物种类夏季出现较多,春季出现较少;91～110 mm体长组出现较多,≤50 mm体长组和>130 mm体长组出现较少。食物多样性指数春季较高,秋季较低;≤50 mm体长组较低,>130 mm体长组较高,食物多样性指数随体长的增加而升高。卡方检验显示,棘头梅童鱼主要食物种类宽尾刺糠虾(Acanthomysis latiscauda)、中国毛虾(Aceteschinensis)、七星底灯鱼(Myctophum pterotum)和中华哲水蚤(Calanus sinicus)的出现频率有极显著的季节变化,中华假磷虾(Pseudeuphausia sinica)的出现频率有显著的季节变化;宽尾刺糠虾和七星底灯鱼的出现频率随体长的变化极显著,而中国毛虾、中华假磷虾和中华哲水蚤的出现频率随体长的变化不显著。聚类分析结果表明,棘头梅童鱼春冬季、夏季和秋季三个时期的食物组成差异显著;体长聚类分两组,即体长>70 mm和≤70mm之间食物组成有明显差异。通过分析发现:东海北部近海棘头梅童鱼食物的季节变化与该海域饵料生物的季节变化密切相关;食物组成随发育的变化符合"最佳摄食理论",其饵料生物种类和大小随棘头梅童鱼体长的增加发生了显著的变化。     

Potential trophodynamic and environmental drivers of steelhead (Oncorhynchus mykiss) productivity in the North Pacific Ocean

Information on prey availability, diets, and trophic levels of fish predators and their prey provides a link between physical and biological changes in the ecosystem and subsequent productivity (growth and survival) of fish populations. In this study two long‐term data sets on summer diets of steelhead (Oncorhynchus mykiss) in international waters of the central North Pacific Ocean (CNP; 1991–2009) and Gulf of Alaska (GOA; 1993–2002) were evaluated to identify potential drivers of steelhead productivity in the North Pacific. Stable isotopes of steelhead muscle tissue were assessed to corroborate the results of stomach content analysis. We found the composition of steelhead diets varied by ocean age group, region, and year. In both the GOA and CNP, gonatid squid (Berryteuthis anonychus) were the most influential component of steelhead diets, leading to higher prey energy densities and stomach fullness. Stomach contents during an exceptionally warm year in the GOA and CNP (1997) were characterized by high diversity of prey with low energy density, few squid, and a large amount of potentially toxic debris (e.g., plastic). Indicators of good diets (high proportions of squid and high prey energy density) were negatively correlated with abundance of wild populations of eastern Kamchatka pink salmon (O. gorbuscha) in the CNP. In conclusion, interannual variations in climate, abundance of squid, and density‐dependent interactions with highly‐abundant stocks of pink salmon were identified as potential key drivers of steelhead productivity in these ecosystems. Additional research in genetic stock identification is needed to link these potential drivers of productivity to individual populations.     

Effects of dietary supplementation of Haematococcus pluvialis powder on gonadal development,coloration and antioxidant capacity of adult male Chinese mitten crab (Eriocheir sinensis)

The green algae Haematococcus pluvialis is an important source of natural astaxanthin as feed additive. This study was conducted to investigate the effects of dietary supplementation of H. pluvialis powder on gonadal development, coloration and antioxidant capacity of adult male Chinese mitten crab Eriocheir sinensis, and four experimental diets were formulated to contain 0, 0.2%, 0.4% and 0.6% of H. pluvialis powder. There were four treatments (defined as D1~D4) in this study and each treatment had three replicates. Dietary H. pluvialis contents had no significant effects on survival, body weight gain rate and gonadal development of male E. sinensis. For colour parameters, the total carotenoids content in carapace and hepatopancreas as well as hepatopancreatic lightness (L*) and carapace redness (a*) increased significantly with increasing dietary H. pluvialis (p < 0.05). For the antioxidant indices in the serum, D4 had the lowest activities of superoxide dismutase (SOD) and peroxidase (POD), but the highest glutathione peroxidase (GSH‐Px) and lactic dehydrogenase (LDH), while the malondialdehyde (MDA) in serum and hepatopancreas decreased significantly with the rising content of dietary H. pluvialis (p < 0.05); D1 had the highest levels of SOD, POD and GSH‐Px in hepatopancreas. For the non‐specific immune indices, the highest activities of acid phosphatase (ACP) and γ‐glutamyl transpeptidase (γ‐GT) were found on the serum of D3 and D4 (p < 0.05). D1 had the highest levels of ACP and alkaline phosphatase (ALP) in hepatopancreas, while D2 and D3 had the lowest levels of ALP and ACP respectively. These results suggested the optimal dietary natural astaxanthin level was around 40 mg/kg diets.     

Effect of insulin in the diet on the growth of European eels (Anguilla anguilla L.)

The effect of oral administration of insulin, in various concentrations, on the growth of European eels (Anguilla anguilla L.) was studied. In order to determine whether the insulin penetrated through the stomach or gills to the blood system, 5 ml insulin, suspended in an 0.6% solution of NaCl, was inserted via the mouth of eels, and the insulin content in the blood measured by radioimmunoassay immediately, and at one and two hours after administration. A control group was given 0.6% NaCl alone. Significantly increased levels of insulin in the blood plasma were found in eels which received high insulin concentrations compared to the control group. Eels administered 20 ppm and 40 ppm insulin in the diet grew significantly faster than a control group fed a diet without insulin, and a group fed 5 ppm insulin.