Factors influencing the spawning success of Oreochromis karongae (Trewavas) in ponds

Fry and fingerlings production of a pelagic tilapia from Lake Malawi, Oreochromis karongae subgenus Nyasalapia (Trewavas), was lower (4.07 ± 5.09, 10–21 fry female⁻¹ month⁻¹) than reported for other tilapias (about 135 fry female⁻¹ month⁻¹). Although seasonality was very pronounced in all experimental systems, the use of net bags (hapas) improved fry yield to 24.7 ± 27.90, 0–354 fry female⁻¹ month⁻¹. Multiple regression analysis demonstrated that the depth of ponds, solar radiation, rainfall and maximum temperature significantly influenced fry and fingerling production (adjusted R²= 0.75; P= 0.0024). Injection of exogenous hormones intramuscularly (pimozide, LH-RHa) induced spawning and significantly (P < 0.05) improved spawning success to a maximum of 998 fry female⁻¹ month⁻¹. As in other cultured tilapias, when placed in fine-meshed net bags, broodstock density was critical to fry production. A density of 1.0 fish m⁻² for broodfish of 120–200 g produced significantly larger numbers of progeny in the hatchery system employed. Spawning was seasonal and restricted to November–February. Broodfish ponds given inputs of chicken layers' mash produced significantly (P < 0.05) higher numbers of fry and fingerlings than maize bran (4.17 vs. 1.22 fry m⁻² female⁻¹ month⁻¹).     

Yield, growth and mortality rate of the Thai river sprat, Clupeichthys aesarnensis, in Sirinthorn Reservoir, Thailand

The Thai river sprat, Clupeichthys aesarnensis Wongratana, is a clupeid with a short life span, and supports artisanal fisheries in a number of reservoirs in the Mekong Basin. The growth parameters, mortality rates and the status of the Thai river sprat in Sirinthorn Reservoir (28 800 ha), NE Thailand (15°N; 105°E), are presented. The fishery is based on lured lift‐nets, operated 7–14 days in the new moon period, September to April each year. It was shown that the von Bertalanffy growth function (VBGF) model was L_t (mm) = 78.43[1 ? exp{?0.211[t ? (?0.7996)]}] and its growth conformed to an isometric pattern. Natural mortality rate (month^?1) was 0.13 month^?1. Total mortality rates ranged from 0.69 to 1.53 month^?1 depending on the weather and the fishing season. Recruitment was continuous throughout the year but peaked in June and July. The yield per recruit model indicated that the exploitation rate of this fishery is probably too high.     

Effect of ammonia-N on growth and feeding of juvenile Macrobrachium rosenbergii (De-Man)

Survival rate, growth and feed intake were determined for late juveniles (4.31 ± 0.18 g) of river prawn Macrobrachium rosenbergii in freshwater with total ammonia‐N (NH₃‐N+NH₄‐N) concentrations of 0.015 (control), 0.5, 1.0 and 1.5 mg L⁻¹ for 60 days at pH 7.53 ± 0.04 and temperature 24.0 ± 2.5°C. Survival rate was significantly (P<0.05) lower (54 ± 4.2–70 ± 5.4%) for total ammonia concentrations from 0.5 to 1.5 mg L⁻¹ [0.0139–0.0419 mg L⁻¹ of unionized ammonia (NH₃)]. Growth (0.026–0.030 g day⁻¹ range) of the prawns did not differ for the different NH₃ levels but were significantly (P<0.05) lower compared with control (0.056 g day⁻¹). Feed intake rates also diminished significantly (P<0.05) from 77.60 ± 2.45% at control (0.015 mg L⁻¹ NH₃‐N) to 48.69 ± 2.13% at 1.5 mg L⁻¹ NH₃‐N (0.0419 mg L⁻¹ of unionized NH₃).     

Effects of dietary mannan oligosaccharide on growth, body composition and hepatopancreas histology of Penaeus semisulcatus (de Haan 1844)

The effects of dietary mannan oligosaccharides (MOS) on growth, body composition and hepatopancreas histology of Penaeus semisulcatus (postlarvae stage 20) were investigated for 48 days. Different dosages of MOS (0, 1.5, 3.0 and 4.5 g MOS kg⁻¹) were tested in triplicate groups. Shrimp postlarvae averaging 0.34 ± 0.01 g attained 1.52 ± 0.31, 1.51 ± 0.15, 2.18 ± 0.13, 1.57 ± 0.13-g final weight and 42.7 ± 2.7, 37.3 ± 1.3, 64.0 ± 6.9, 50.7 ± 4.8% survival, respectively. At the end of the study, generally enhanced growth performance and feed conversion ratio were observed in shrimp fed on diet containing 3.0 g kg⁻¹ MOS with the highest final live weight (2.18 ± 0.13 g) and survival rate (64.0 ± 6.9%) after 48 days of feeding. The protein contents in the whole body decreased with increasing rates of dietary MOS (P < 0.05). Different levels of dietary MOS used in this study showed no detrimental effects on hepatopancreas tissue judged by histological screening. In conclusion, 3.0 g kg⁻¹ MOS could be used as a healthy growth promoter in shrimp diets.     

Growth and survival of juvenile lined seahorse,Hippocampus erectus (Perry), at different stocking densities

The lined seahorse, Hippocampus erectus (Perry), is an important species in both medicinal and aquarium trades. The aim of this study was to evaluate the effects of stocking density (1, 3 and 5 individuals L⁻¹) on the growth performance and survival of the early-stage juvenile H. erectus. The height (HT), wet weight, weight gain (WG) and specific growth rate (SGR) were affected significantly by the stocking density during the 40-day study. The HT, WG and SGR of the seahorse at 1 and 3 juveniles L⁻¹ were significantly higher than that at 5 juveniles L⁻¹. The survival of juveniles at the three stocking densities was not significantly different at day 25 (90.3 ± 4.5%, 86.7 ± 4.2% and 86.2 ± 3.8% for 1, 3 and 5 juveniles L⁻¹ respectively), but was significantly different at day 40 (87.8 ± 3.9%, 69.6 ± 4.2% and 52.9 ± 2.8% for 1, 3 and 5 juveniles L⁻¹ respectively). For the early-stage juvenile H. erectus, we recommend a stocking density of 3 juveniles L⁻¹, but the density should be reduced to 1–2 juveniles L⁻¹ to avoid reduced and variable growth and high mortality after 25 days.     

Dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (Hamilton)

An 8‐week feeding experiment was conducted to quantify the dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (3.50 ± 0.04 cm; 0.40 ± 0.02 g) using amino acid test diets (400 g kg⁻¹ crude protein; 17.90 kJ g⁻¹ gross energy) containing casein, gelatin and l ‐crystalline amino acids. Six dietary treatments supplemented with graded levels of isoleucine (7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 g kg⁻¹), in gradations of 2.5 g kg⁻¹ diet, were fed to triplicate groups of fingerlings to apparent satiation divided over two feedings at 07:00 and 17:30 h. Performance of the fish was evaluated on the basis of live weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR) and protein productive value (PPV). Statistical analysis of live weight gain, FCR, PER, SGR and PPV reflected significant differences among treatments. Live weight gain and conversion efficiencies were best with isoleucine at 15.0 g kg⁻¹ of diet. Live weight gain, FCR, PER, SGR and PPV data were also analysed using second‐degree polynomial regression analysis to obtain more accurate isoleucine requirement estimate which was found to be at 15.9, 15.3, 15.2, 15.8 and 15.7 g kg⁻¹ of dry diet, corresponding to 39.8, 38.3, 38.0, 39.5 and 39.3 g kg⁻¹ of dietary protein respectively. Based on the quadratic regression analysis of the live weight gain, FCR, PER, SGR and PPV, the optimum level of isoleucine for fingerling L. rohita is in the range of 15.2–15.9 g kg⁻¹ of dry diet, corresponding to 38.0–39.8 g kg⁻¹ of dietary protein. Maximum body protein, minimum moisture and fat were noted at 15.0 g kg⁻¹ of dietary isoleucine while the body ash remained constant among all the treatment levels. No mortality was recorded during the duration of the experiment.     

Influence of different sources and levels of dietary protein and lipid on the growth,feed efficiency,muscle composition and fatty acid profile of Snakehead Channa striatus (Bloch, 1793) fingerling

Nine isoenergetic (18.5 kJ g⁻¹) diets were formulated, in a 3 × 3 factorial design, by varying three levels of dietary protein (350, 400 and 450 g kg⁻¹) at each of three levels of dietary lipid (65, 90 and 115 g kg⁻¹) accordingly. Each diet was hand fed two times daily for 8 weeks to triplicate homogenous groups of eight fish (average weight 3.34 ± 0.02 g) per tank connected to a recirculation system. Results showed that the feed efficiency and growth performance significantly (P<0.05) increased with increasing protein level at the two lower lipid levels (65 and 90 g kg⁻¹), respectively, as indicated by indices such as %weight gain, specific growth rate, protein efficiency ratio, feed conversion ratio and feed intake, but did not at the highest lipid level (115 g kg⁻¹). The muscle polyunsaturated fatty acids (PUFA) content declined with increasing dietary protein level at the lipid levels producing the highest growth, suggesting that the utilization of PUFA influences growth. Whereas the muscle monounsaturated fatty acids level was generally lower than the dietary levels in all the treatments tested, indicating preferential catabolism for energy, the muscle saturated fatty acids level was comparatively higher than in the diets, indicating selective deposition. Docosa hexaenoic acid (22:6n3, DHA), which was very low in the diet and in the initial fish, was higher in the muscle of some of the treatments, indicating the ability of Channa striatus to desaturate and elongate short‐chain PUFA to long‐chain HUFA, due to the availability of dietary 18:3n3 and 20:5n3 (the precursors for DHA biosynthesis). It could be concluded, based on the results of this trial, that a diet formulated to contain 65 g kg⁻¹ lipid and 450 g kg⁻¹ protein, with a gross energy of 18.5 kJ g⁻¹ and a dietary n3/n6 PUFA ratio of about 0.1, is sufficient to promote good feed efficiency and growth performance in C. striatus fingerling.     

Growth and mortality of Mediterranean mussel Mytilus galloprovincialis Lam., 1819, in relation to size on longline in Mersin Bay, Izmir (Turkey – Aegean Sea)

The growth and mortality rate of different size of mussels, Mytilus galloprovincialis, were compared in Mersin bay, Izmir. Mussel sampling was performed on a monthly basis over 1 year, together with hyrobiological parameters. Water temperature, salinity, chlorophyll a, total particulate matter (TPM) and particulate organic carbon (POC) were determined. Average chlorophyll a, TPM and POC values were 3.88±1.62 μg L⁻¹, 13.12±3.68 mg L⁻¹ and 252±121.89 μg L⁻¹ respectively. Initial mean lengths of mussels for each size group were 10 mm (9.91±0.25 mm), 20 mm (20.14±0.29 mm), 30 mm (30.66±0.21 mm), 40 mm (40.14±0.21 mm), 50 mm (50.62±0.21 mm), 60 mm (59.77±0.21 mm) and 70 mm (69.47±0.62 mm). Maximum growth in length occurred during the spring–summer months. The annual length increments of mussel size groups were 46.22, 41.42, 30.3, 28.03, 20.63, 16.34 and 12.03 mm from small to large size groups respectively. Small mussels grew faster than large mussels and reached commercial size at the same time. Mortality was <5% for all groups at the end of the experiment.     

Dietary arginine requirement of fingerling hybrid Clarias (Clarias gariepinus×Clarias macrocephalus)

The dietary arginine requirement of fingerling hybrid Clarias (Clarias gariepinus×Clarias macrocephalus) (4.2±0.03 cm, 0.56±0.04 g) was determined by feeding six isonitrogenous (400 g kg⁻¹ crude protein) and isocaloric (17.9 kJ g⁻¹) amino acid test diets containing casein, gelatin and l ‐crystalline amino acids with graded levels of arginine (10.0, 12.5, 15.0, 17.5, 20.0 and 22.5 g kg⁻¹) for 4 weeks to triplicate groups. Diets were fed twice a day at 09:00 and 16:00 hours at 8% body weight day⁻¹. Maximum weight gain (523%), best feed conversion ratio (FCR, 1.41), protein efficiency ratio (1.78) and specific growth rate (6.53%) were recorded in fish fed the diet containing arginine at 20.0gkg⁻¹ of the diet. Second‐degree polynomial regression analysis of live weight gain and FCR values indicated the dietary arginine requirement at 17.8 and 20.0 g kg⁻¹ of dry diet respectively. Significantly higher carcass protein and protein deposition values were recorded at the requirement level (20.0 g kg⁻¹). Higher fat and lower moisture values were obtained in carcass of fish fed the diet with 15.0g kg⁻¹ arginine. The maximum carcass ash value was noticed in the fish fed at 20.0 g kg⁻¹ dietary arginine. We recommend that the diet for hybrid Clarias (C. gariepinus×C. macrocephalus) should contain arginine in the range of 17.8–20.0 g kg⁻¹ of the dry diet, corresponding to 44.5 and 50 g kg⁻¹ of dietary protein respectively.     

Digestibility and performance of pacu (Piaractus mesopotamicus) juveniles — fed diets containing different protein, lipid and carbohydrate levels

Due to lack of information on the use of non‐protein energy sources in diets for pacu (Piaractus mesopotamicus), a 2 × 2 × 3 factorial experiment was conducted to evaluate the performance and digestibility of 12 diets containing approximately two crude protein (CP; 220 and 250 g kg⁻¹), two lipid (40 and 80 g kg⁻¹) and three carbohydrate levels (410, 460 and 500 g kg⁻¹). The pacu juveniles‐fed diets containing 220 g kg⁻¹ CP did not respond (P > 0.05) to increased dietary lipid and carbohydrate levels, but the fish‐fed diets containing 250 g kg⁻¹ CP showed a better feed conversion ratio. There were interactions in weight gain (WG), specific growth rate (SGR), crude protein intake (CPI) and feed conversion rate (FCR) dependent on dietary carbohydrate and lipid levels, showing positive effects of increasing carbohydrate levels only for fish‐fed diets containing 80 g kg⁻¹ lipid level. However, when the diets contained 40 g kg⁻¹ lipid, the best energy productive value (EPV) results were obtained at 460 g kg⁻¹ carbohydrate. A higher usage of lipids (80 g kg⁻¹) reduced CPI and was detrimental to protein [apparent digestibility coefficient (ADC)_CP] and energy (ADC_GE), but did not affect growth. The ADC_GE improved proportionally as dietary carbohydrate levels increased (P < 0.05), increasing the concentration of digestible energy. In addition, the WG, CPI, ADC_GE results showed best use of the energy from carbohydrates when dietary protein level was 250 g kg⁻¹ CP. The utilization of 250 g kg⁻¹ CP in feeds for juvenile pacu for optimal growth is suggested. Therefore, the optimum dietary lipid and carbohydrate levels depend on their combinations. It can be stated that pacu uses carbohydrates as effectively as lipids in the maximization of protein usage, as long as it is not lower than 250 g kg⁻¹ CP or approximately 230 g kg⁻¹ digestible protein.     

Mass culture of fairy shrimp Streptocephalus proboscideus (Crustacea – Anostraca) and its use in larviculture of the Persian sturgeon, Acipenser persicus

This study was conducted with cysts of Streptocephalus proboscideus obtained from the University of Gent‐Belgium. The cysts were hatched in Environmental Protection Agency (EPA) medium. The nauplii were reared at the Sturgeon Research Institute using a pure culture of Scenedesmus obliquus alga supplied at a density of 5 × 10³ cell mL⁻¹ that gradually increased to 1 × 10⁴, 5 × 10⁴ and 1 × 10⁵ cell mL⁻¹ with the growth of the nauplii. The nauplii attained sexual maturity and started producing cysts in 8 days and yielded a mean cyst number of 220±40 female⁻¹ brood⁻¹ cysts. These cysts were used in the larviculture of Persian sturgeon, Acipenser persicus (Borodin). Forty‐three larvae of Persian sturgeon (mean weight: 15.4±1.1 mg; mean length: 27.1±2.7 mm) with roughly absorbed yolk sacs were stocked in three aquaria and fed S. proboscideus nauplii at 8‐h intervals. By the end of the experiment (day 5), the mean weight and length of Persian sturgeon larvae were 51.4±13.3 mg and 20.7±1.4 mm respectively.     

Effect of plant protein concentrates on nutrition physiology of Litopenaeus vannamei (Boone, 1883) juveniles

This study was designed to test the effect of soy protein (SPC), wheat gluten (WHG) and potato protein (PPC), in vitro and in vivo digestibility of protein and energy in the juveniles Litopeneaus vannamei. A completely random design was used with nine 400‐L tanks (with three repetitions by treatment). Ten respirometric chambers (500 mL) were used for energy distribution. In vitro digestibility for SPC (8.8%) was higher than for PPC (5.8%) and for WHG (4.3%, P < 0.05). Diets’ degree of hydrolysis ranged between 0.75% and 1.2%, with lowest value in potato protein concentrate diet (0.75 ± 0.09%, P < 0.05). No significant differences were obtained in apparent digestibility coefficient (ADC) for protein (63.4–74.1%). ADC for amino acids ranged between 80% and 90%. Daily growth coefficient ranged from 0.86% to 1.1% day⁻¹, being the best in soybean protein concentrate diet (SPCd) (P < 0.05). Significant differences on heat increment were observed (P < 0.05); highest value was in wheat gluten diet (1.0 ± 0.1 kJ shrimp day⁻¹) that coincided with a peak of trypsin specific activity (16.5 ± 3.7 mU mg protein⁻¹). Highest retained energy for growth was observed in shrimp fed SPCd (0.7 ± 0.03 kJ day⁻¹, P < 0.05). Muscle collagen content presented a minimum of bands with SPCd, whereas shrimp post‐mortem collagenase activity was not affected by any of the three diets (P > 0.05).     

Effects of enriched Artemia nauplii on production, survival and growth of the mysid shrimp Mysidopsis almyra Bowman 1964 (Crustacea: Mysidacea)

The effects of enriched Artemia nauplii on larvae production and survival and growth of the mysid Mysidopsis almyra Bowman 1964 are compared. There were no significant differences (P > 0.05) in production between mysids fed the Artemia nauplii (133 ± 69 mysids day⁻¹) and mysids fed the enriched nauplii (139 ± 82 mysids day⁻¹). No differences in size of newly hatched mysids or mysid growth to 15 days (P > 0.05) were found between the two diets. Survival was significantly higher (P < 0.05) for mysids fed the enriched nauplii (59.1%) compared with mysids fed Artemia nauplii (41.4%).     

Effects of dietary supplementation of fructooligosaccharide on growth performance,body composition,intestinal enzymes activities and histology of blunt snout bream (Megalobrama amblycephala) fingerlings

A feeding trial was conducted to investigate the effects of dietary fructooligosaccharide (FOS) on growth performance, body composition, intestinal enzymes activities and histology of fingerling Megalobrama amblycephala. A total of 1200 fish (1.42 ± 0.01 g) were fed diets containing graded levels of FOS (0, 0.5, 1, 2, 4 and 8 g kg⁻¹ diet) for 8 weeks in a recirculating system indoor. The weight gain, specific growth rate (SGR) and survival rate were all improved in dietary supplementation of FOS fed fish. Increasing FOS levels resulted in both higher whole‐body lipid and lower moisture contents, whereas ash and protein contents showed no significant differences among all the treatments. Intestinal amylase, protease, Na⁺, K⁺‐ATPase, alkaline phosphatase, γ‐glutamyl transpeptidase and creatine kinase activities all increased with dietary FOS levels up to 4 g kg⁻¹ (P < 0.05). Transmission electron microscopy analysis indicated that microvilli length in the mid‐intestine was significantly increased with increased dietary FOS levels (P < 0.05). In conclusion, dietary supplementation of FOS could confer benefits on growth performance, intestinal digestive and absorptive ability, histology of fingerling Megalobrama amblycephala.     

The effect of feed supply rate on growth of juvenile perch (Perca fluviatilis)

This study investigates the effect of the feed supply rate within a meal on growth of juvenile perch (Perca fluviatilis). Groups of PIT-tagged, feed-trained juvenile perch (12 g) were held in 100-L tanks at 18 °C, under a 24L:0D photoperiod and fed five meals per day in excess. Feed was applied at rates of 1.2 (Low), 4.2 (Medium) and 14.3 (High) pellets fish⁻¹ min⁻¹ during two periods, each of 50 days. Cumulative meal-time per day ranged from 10 to 225 min. Specific growth rates (SGR) in the two periods were positively correlated, indicating a consistent individual growth performance. There was growth dimorphism between the sexes. Females grew about 20% faster than males, resulting in final mean weights of ≈ 87 and 58 g respectively. Autopsy revealed differences in sex ratios between treatments and the effect of feeding rate was analysed according to sex. There was a tendency for fish fed at the lowest rate to have a higher SGR than fish in other treatments, both for females (L = 1.98 ± 0.0, M = 1.84 ± 0.08, H = 1.88 ± 0.19% bw day⁻¹) and males (L = 1.68 ± 0.01, M = 1.55 ± 0.16, H = 1.57 ± 0.02% bw day⁻¹). Fish fed at the lowest rate also tended to have the lowest feed conversion ratio (L = 0.88 ± 0.05, M = 1.02 ± 0.11, H = 1.04 ± 0.10) but the effects were not significant. These results suggest that juvenile perch can feed efficiently under a range of conditions.     

Protein-sparing effect of carbohydrate in silver barb, Puntius gonionotus fry

A 30‐day study was undertaken to examine the protein‐sparing effect of carbohydrate in diets for silver barb, Puntius gonionotus fry. Six semi‐purified experimental diets were formulated with two levels of protein (200 and 250 g kg⁻¹ diet) and three levels of carbohydrate (300, 340 and 380 g kg⁻¹ diet). In addition to the six experimental diets, a diet containing the protein and carbohydrate requirement levels of 300 and 260 g kg⁻¹ diet, respectively, as reported earlier for this species, was used as a reference diet. For each dietary treatment, 30 healthy fry of 20 days age (0.12 ± 0.01 g) were stocked in triplicate tanks using a flow‐through system. The fish were fed ad libitum four times a day to a level close to apparent satiation. Batch weighing of fish was done after 15 days of stocking to measure growth and general health status of the fish. The fish fed 250 g protein and 340 g carbohydrate kg⁻¹ diet with a protein to energy ratio of 17.86 g protein MJ⁻¹ performed equally well in terms of growth and nutrient utilization as the reference diet group. The study indicates that dietary protein can be reduced from 300 to 250 g kg⁻¹ diet by increasing carbohydrate from 260 to 340 g kg⁻¹ diet without sacrificing the growth of silver barb fry.     

Effects of stocking density on growth, yield and profitability of farming Nile tilapia, Oreochromis niloticus L., fed Azolla diet, in earthen ponds

Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand‐fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g⁻¹) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by‐products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P<0.05), but same profitability values were obtained with all diets (P>0.05). In experiment 2, three stocking densities, 1, 3 and 5 m⁻², were assigned to three treatments T₁, T₂ and T₃ respectively. Fish were hand‐fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day⁻¹), the specific growth rate (1.90–2.20% day⁻¹) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P<0.05) at 5 m⁻², compared with the other densities. Stocking density did not affect survival rate (P>0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are⁻¹ and 28.79 ± 3.66 to 101.42 ± 7.48 kg are⁻¹ year⁻¹, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m⁻² produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m⁻² with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.     

Effect of dietary protein on growth, feed conversion, body composition and survival of pike perch fingerlings (Sander lucioperca)

Triplicate groups of pike perch (Sander lucioperca) juveniles were fed six experimental diets containing protein levels varying from 263 to 619 g kg⁻¹ dry matter (d.m.) for 56 days. Dietary protein was supplied by graded amounts of fish meal (with 720 g kg⁻¹ crude protein). Crude lipid and gross energy content of 101–107 g kg⁻¹ and 19.9–20.6 MJ kg⁻¹ remained constant between experimental diets. Pike perch with an initial body weight of 1.05 ± 0.05 g were randomly distributed in 18 tanks of two similar recirculation systems and fed on gradually decreasing feeding rates of 10 to 6% of their body weight per day. Growth performance and feed conversion increased with dietary protein level from 263 to 549 g kg⁻¹ d.m. but did not decline at highest dietary protein level. Protein efficiency ratio declined linearly with increasing dietary protein. Survival ranged between 89.7 and 93.9% and was not affected by dietary composition. Dry matter and crude lipid content of pike perch fingerlings decreased with increasing dietary protein supply and significantly the lowest dry matter and crude lipid levels were observed in fish fed diets containing 619 g kg⁻¹ of crude protein. The dietary protein requirement for pike perch fingerlings calculated by broken‐line and second‐order polynomial regression ranged between 529 and 577 g kg⁻¹, respectively.     

Effect of varying dietary energy level on feed intake, feed conversion, whole-body composition and growth of Malawian tilapia, Oreochromis shiranus– Boulenger

Four isonitrogenous [30% crude protein (CP)] diets containing different gross energy levels (13.39, 16.74, 20.50 and 23.85 kJ g⁻¹) were evaluated to determine the optimum energy for the Malawian tilapia Oreochromis shiranus. Each tank (120 L) was stocked with 18 juvenile tilapia (average weight 7.32±0.25 g) and they were fed the experimental diets for 10 weeks. The final average weight of the fish was approximately twofold higher (range: 12.64–16.77 g) than the initial weight. The dietary energy significantly (P<0.05) influenced growth. The average weight of fish fed dietary energy level 20.50 kJ g⁻¹ was significantly higher (P<0.05) than the weight of the fish fed any of the other experimental diets. There was no significant difference in growth of fish fed 13.39 and 16.74 kJ g⁻¹ energy levels, but 23.85 kJ g⁻¹ produced the lowest growth rates. There were no significant differences (P>0.05) between feed intake across the treatments. Feed conversion ratio (range: 2.2–3.0) and protein efficiency ratio (range: 1.10–1.50) among the dietary treatment groups were in agreement with trends for weight gain. Dietary energy level significantly (P<0.05) influenced the body composition of O. shiranus. Whole‐body moisture (range: 64.27–67.15%) and ash (range: 13.21–14.73%) decreased in all treatments. Whole‐body protein (range: 63.57–66.16%) increased only in groups fed on the diet containing 20.50 kJ g⁻¹. Whole‐body fat (range: 13.58–17.27%) and gross energy (range: 28.411–33.210 kJ g⁻¹) increased significantly (P<0.05). Fish survival was 100% in all treatments. The results demonstrated that to maximize growth at a temperature of 23°C, O. shiranus should be fed diets containing 20.50 kJ g⁻¹ gross energy.     

Sperm density, seminal plasma composition and their physiological relationship in the endangered Caspian brown trout (Salmo trutta caspius)

Sperm density, mineral and organic composition of the seminal plasma and their physiological relationship were investigated in the Caspian brown trout (Salmo trutta caspius). To establish a rapid and accurate method for assessment of sperm density, three different techniques were used: sperm counting, spectrophotometry (at 480 nm) and determination of the spermatocrit. The seminal plasma contained 159.26±8.84 mM sodium (Na), 33.72±2.01 mM potassium (K), 133.04±5.96 mM chlorine (Cl), 1.68±0.2 mM calcium (Ca) and 0.988±0.13 mM magnesium (Mg). The following organic components were found: total protein 0.75±0.14 mg 100 mL⁻¹, cholesterol 2.86±0.58 mg L⁻¹ and glucose 3.81±1.04 mM L⁻¹. The mean sperm density was estimated to be 3.3 × 10⁹ spermatozoa mL⁻¹. The spermatocrit (%) ranged from 25 to 52 in sperm samples. Highly significant linear relationships were found between sperm density and spermatocrit (R²=0.703, P<0.001) and sperm density and optical density (R²=0.909, P<0.001), indicating that optical density can be used as a quick and accurate method of estimating sperm density. Significant relationships were also found between sperm density and Ca, Mg and total protein of seminal plasma. A significant correlation was also observed between the Ca and Mg concentrations (R²=0.774, P<0.01). The following correlations were observed between mineral and organic components: total protein and Ca (R²=0.462, P<0.05), total protein and Mg (R²=0.518, P<0.05) and glucose and Cl (R²=0.374, P<0.05). These parameters should be considered when developing procedures for either artificial fertilization or for cryopreservation of sperm.