Edo D’Agaro

Alternative plant protein sources in sea bass diets

Abstract A control diet (C) containing animal protein (mainly fish meal) was compared with 6 experimental diets containing different plant proteins (soybean meal, SM; rapeseed meal, RM; potato protein concentrate, PPC and a mix of the three vegetable protein sources, M). The plant protein replaced either 25 (1) or 50 (2)% of the animal protein with the exception of diet RM2 where the substitution rate was lowered to 35%, and in diet M where 55% of the total protein given was replaced in equal amounts by the three plant proteins. For the growth trial, which lasted 97 days, 528 European sea bass (initial live weight 107 ± 0,06g), distributed among 24 fibreglass tanks with three replicates per treatment, were used. The pelleted feed was distributed 5 times per day using an automatic dispenser. Energy, crude protein and crude fat digestibility values for fish meal and soybean meal were similar and not statistically different while the values for rapeseed meal and potato protein concentrate were significantly lower. Digestive utilization for NFE was higher in fish meal and decreased significantly in soybean meal, rapeseed meal and even more noticeably in potato protein concentrate. Diet digestibility values showed a similar trend with a clear worsening effect at the higher inclusion rates used. Diet M gave digestibility coefficients lower than those observed with diets C, SM1, SM2, RS1 and RS2 and higher than those of diets PPC1 and PPC2. Fish fed a diet in which 25% of the total protein was replaced by soybean had similar performances to those of the control group. On the other hand, sea bass fed diets SM2, RS1, RS2 and M had lower growth rates and worse feed utilization than those observed with the control. Finally, specific growth rates and food conversion efficiency in sea bass fed diets containing potato protein concentrate were poor because of the low palatability. These results show that soybean meal can substitute up to 25% of the total protein of the diet without any negative effect on sea bass performance.

Environmental impact of sea bass cage farming in the north Adriatic Sea

Abstract The main objective of the research was to reduce the organic and nutrient load under the net pen fish farms. An experiment was conducted to study the effects of artificial barriers fixed under a set of sea cages in order to reduce the environmental impact. The artificial barriers were made of four submerged galvanized steel pipes coated with plastic and placed on the sea floor (10 m depth) in the Trieste gulf. The experimental design was as follows: control (C), cages with barriers (B), cages without barriers (WB). Measurements were taken on the surface as well as at 4 and 8m of depth. The trial lasted from the end of June 2000 to December 2001. Water quality parameters were not significantly influenced by the fish cages. Surface samples were characterised by lower levels of salinity and higher levels of oxygen and nitrate compared to those taken at 4 and 8 m. The artificial barriers favoured the establishment of a rich epiphytic fauna that took advantage of the presence of organic matter derived from fish cages. The two species Nucula nucleus and Neanthes caudata and the total bacterial counts were identified as potential indicators of pollution under the fish cage farms.

Growth parameters in European sea bass (Dicentrarchus labraxL.): effects of live weight and water temperature

Abstract The voluntary feed intake (VFI) and growth rate of sea bass were studied for 147 days, based on different starting live weights, under natural photoperiods and varied water temperatures. Sea bass (n = 720) were divided into five weight classes (60–70, 90–110, 130–150, 160–180 and 230–250 g) and distributed among 20 tanks. Seven different water temperatures were compared: 13, 16, 19, 22, 25, 28 and 31 °C. A commercial extruded diet (N x 6.25, 43.7% DM; crude fat, 25.7% DM) was used. The trial was performed in a closed-circuit plant, with a daily water turnover rate of 10%. Each tank was fitted with an apparatus for collecting the uneaten food. Automatic feeders distributed equal amounts of food for ten meals per day. The daily food allowance was adjusted, based on fish biomass, to permit ad libitum feeding and to leave approximately 20% uneaten. Fish were exposed to natural photoperiod (March-July). Non-linear regression equations were used to calculate the best-fitting curves for the data.

Effects of dietary energy content on the voluntary feed intake and blood parameters of sea bass (Dicentrarchus labrax L.)

Abstract Energy and protein requirements of sea bass for maximum growth and fasting energy requirements were determined by using three diets containing increasing DE levels and two fish weights. Five hundred and sixteen sea bass were divided in two body weight (BW) classes (A: 67.7 ± 0.85g and B: 128.6 ± 0.88g, mean ± SD live weight) and randomly distributed among 24 tanks. They were fed for 12 weeks on three isoproteic diets characterized by different levels of digestible energy (DE): low energy (LE), 18.6; medium energy (ME), 19.7; and high energy (HE), 22.6 MJ kg-1 dry matter (DM). The entire trial lasted 113 d and was divided into two periods: a feeding trial of 83 d and a fasting trial of 30 d. Specific growth rates decreased in fish fed on the HE diet (P < 0.05), but only in fish weighing 68 g. Voluntary feed intakes and feed conversion ratios were inversely related to dietary energy contents in both weight classes. During the starvation trial, body depletion increased (P<0.05) in fish fed on high-energy diets during the feeding experiment. The gross energy requirements (per day) for maximum growth were 320 and 221 kJ kg-1 BW for fish weighing 68 g and 128 g, respectively. Fasting metabolisms were 60.6 and 54.1 kJ kg–0.83 BW per day for fish weighing 68g and 128g, respectively. It is concluded that growth performance of sea bass appear to be dependent on digestible dietary energy. Gross energy intake, net energy (production) and maintenance requirements of fish were not influenced by dietary treatments.

Induction of ovarian maturation by means of dietary hormonal treatment in Austropotamobius pallipes

Riassunto Induzione della maturazione ovarica mediante l’impiego di ormoni di sintesi nel gambero Austropotamobius pallipes. Lo scopo della presente ricerca era quello di indurre la riproduzione nel gambero autoctono Austropotamobius pallipes in ambiente controllato. A tal fine, 33 femmine adulte di Austropotamobius pallipes sono state alimentate durante un periodo non riproduttivo (febbraio-aprile) con diete contenenti sostanze ormonali di sintesi (ormone giovanile III, 17α-idrossiprogesterone, 17α-idrossiprogesterone + ormone giovanile III) per stimolare la maturazione ovarica. Vennero utilizzate per l’esperimento due gruppi d animali: il primo in cui le femmine si erano già riprodotte l’anno precedente e il secondo in cui non si eran riprodotte. Alla fine dell’esperimento, l’indice gonadosomatico e il diametro degli oociti aumentarono significati- vamente negli animali trattati con l’ormone giovanile III rispetto al controllo. Venne inoltre osservata la produ zione di vitellogenine emolinfatiche del peso di 105 e 164 Kda rispetto al controllo. L’ormone giovanile III somministrato con l’alimento ha esercitato un effetto positivo sullo sviluppo ovarico di tutte le femmine nella specie A. pallipes durante un periodo non riproduttivo.

Weaning experiments with Dover sole (Solea solea) larvae

Abstract Two experiments were performed in an hatchery; in the first 520 sole larvae, average live weight (a.l.w.) 37 mg, 52 dah, were distributed among 8 net cages and fed two microdiets, for 55 days (d). Protein, fat, EPA contents were: 64.1 and 62.6; 21.9 and 18.5% on d.m.; 8.9 and 9.0% of fat respectively for diet A and B. Artemia enriched naupli (AEN) were distributed for 28 d, at 5 (1st week), 3 (2nd w.) and 2 units/ml (3rd and 4th ws.). In the secon trial 1040 sole larvae, a.l.w. 69 mg, 87 dah, were distributed among 16 net cages (4 replicates, diet A and B,8