Pierre Luquet

Digestibility in fish: Improved device for the automatic collection of feces

Abstract An improved apparatus for the quantitative automatic collection of fish feces is presented. The drainage water from fish tanks is filtered through metallic screens that separate feces from water as they move linearly. With an abrupt stop of the screens, the feces are injected into a refrigerated pan where they are automatically frozen. The system is limited only by the capacity of the collector pans. With this quantitative recovery of feces, the direct method may be used for digestibility determinations on natural or artificial foodstuffs. Furthermore, this apparatus may be used with species where feces collection by abdominal pressure for digestibility measurements is not possible.

Studies on the nutrition of Siberian sturgeon, Acipenser baeri: I. Utilization of digestible carbohydrates by sturgeon

Abstract A growth trial was conducted to study the effects of incorporation of four different carbohydrate sources (crude, gelatinized or extruded starch, extruded whole corn) in practical diets (crude protein level: 36%) for Siberian sturgeon, Acipenser baeri. Another diet incorporating gelatinized starch was formulated at a higher protein level of 42%. Based on growth performance, body composition and nutrient retention efficiencies, it was found that growing juvenile Siberian sturgeon do not utilize well complex carbohydrates like crude starch. Extruded or pregelatinized starches or extruded corn can be used as an energy-yielding ingredient in sturgeon grower diets. The level of feeding has a great impact on feed efficiency, the optimal level being 1.45% of body weight per day for sturgeon weighing between 90 and 400 g. The results indicate that the protein requirement for optimal growth of Siberian sturgeon would be around 36%, but below 42%. In absolute terms, the daily protein requirement for optimum growth would amount to 3.7 g digestible protein/kg BW per day with a protein:energy ratio of 18 mg digestible protein/kJ DE. Histological studies revealed that high levels of digestible carbohydrates adversely affect liver size, morphology and function.

Influence of bacterial protein incorporation and of sulphur amino acid supplementation to such diets on growth of rainbow trout, Salmo gairdnerii Richardson

Abstract A single cell protein (SCP) of methanophillic bacterial origin was incorporated into rainbow trout diets, at increasing levels of substitution for fish meal. Growth characteristics of rainbow trout fed these diets with or without sulphur amino acid supplementation (SAA) were followed over an experimental period of 16 weeks. It appeared from the results that this novel protein could replace nearly 80% of fish meal with no adverse effects on overall performance. Feed intake was adversely affected when the SCP was the major source of protein. Digestibility of protein was found to be increased at high levels of incorporation of the SCP. Effects of an addition of sulphur amino acids (L- or DL-methionine or L-cystine) to diets with 14% SCP or without SCP were also observed. Supplementation of these diets with the different SAA depressed trout growth to varying degrees. It was found that L-cystine had a more depressive effect than L-methionine, which in turn had a greater effect than DL-methionine. These results are discussed in the light of recent data on the SAA needs of rainbow trout. This study revealed that total substitution of fish meal in trout diets was feasible, and that there was no need for further supplementation with sulphur amino acids in the type of compounded diets used in this study.

Influence of environmental temperature on flow rate of foodstuffs through the gastrointestinal tract of rainbow trout

Abstract Experiments were carried out with rainbow trout ( Salmo gairdneri ) to determine the rate of passage of foodstuffs through the digestive tract, before and after a rise in environmental temperature from 9–10°C to 18°C in 1 day. Transit rate was analyzed from the rate of fecal excretion of a marker (Cr 2 O 3 ) incorporated in the diet. In a first experiment on trout weighing about 80 g, mean retention time (MRT) (Castle, 1956) and mean transit time (MTT) (Zierlier, 1958) of the marker, starting from the 9°C acclimated values (34 h for MRT and MTT), decreased as early as the first day after the temperature change (24 and 26 h respectively) and reached the 18°C acclimated values (19 and 21 h respectively) in 4–7 days. In a second experiment on trout weighing about 140 g the pattern of response of MRT and MTT to the temperature increase was similar to that observed in the first experiment: they were 27 and 29 h at 10°C, 16 and 19 h on the second day after the temperature change, and 13 h and 15 h after acclimation at 18°C, respectively. These changes related to environmental temperature were independent of any increase in food consumption. The differences in transit rate of marker between the two experiments could be attributed to the higher body weight and food consumption in the second experiment. Excretion of Cr 2 O 3 in the feces was analyzed in the second experiment through a four-compartment model involving the stomach, anterior and posterior intestine, and feces. Fractional evacuation rate of marker in each digestive tract compartment was calculated according to the model. All compartments were affected by the temperature increase. There was a transitory acceleration of transit rate, observed principally in the stomach. These alterations were achieved by the eighth day after the temperature change and it was concluded that acclimation to the new temperature was accomplished in 1 week.

Practical diet for mass culture of the rotifer Brachionus plicatilis: Application to larval rearing of sea bass, Dicentrarchus labrax

Abstract Different trials were undertaken to substitute a prepared diet for freeze-dried algae Platymonas suecica , as food for Brachionus plicatilis in continuous culture with renewal of a quarter of the volume daily. Good yield, steady for a month, was obtained only with a 60 l tank, with water of medium salinity (about 18‰) and with 33% of the ration as freeze-dried algae: about 120 Brachionus were produced per ml per day in this way, twice the level obtainable with living algae. When, in three experiments, rotifers fed on the prepared diet and freeze-dried algae in a proportion of 3:1 were given to sea bass larvae, the growth of the latter was not reduced, whereas their survival rates (25, 27 and 11% at the 25th or 20th day) were more constant than with algae-fed rotifers (respectiely 24, 3 and 1%). Better survival rates were obtained when rotifers were enriched with a nutrient mix just before pouring into tanks of larvae (50 and 16%).

Influence of dietary amino acid patterns on the free amino acid contents of blood and muscle of rainbow trout (Salmo gairdnerii R.).

1. Groups of rainbow trout were given one or other of two diets that differed in amino acid profile for two months; concentrations of free amino acids in whole blood and latero-dorsal muscle were then measured. The effects of temperature (12 and 18 degrees C in freshwater) and salinity on the concentrations of free amino acids in these tissues were also observed. 2. Although both diets apparently met the essential amino acid requirements of the trout and were isoenergetic, they nevertheless had different nutritional values for trout. 3. Patterns of free amino acids in tissues of trout given the two diets were different. Blood and muscle amino acid fractions were affected differently by changes in dietary amino acids.

Continuous Quantitative Automatic Collector for Fish Feces

Abstract A method for the automatic collection of fish feces is described. Drainage water from fish tanks is filtered through revolving hemispheric metallic screens which quickly remove feces from the water and propel them into a refrigerated pan, where they are immediately frozen. Operation of the system-requires minimal attention and is not time-consuming. As indicated by the total collection of an inert tracer, chromic oxide, this method enables quantitative recovery of feces and makes digestibility determinations possible, even by the direct method.

Effect of dietary fatty acids differing by chain lengths and ω series on the growth and lipid composition of turbot Scophthalmus maximus L.

1. A previous paper (Gatesoupe et al., 1977) showed that turbot had a specific requirement for omega 3HPUFA since equivalent dietary amounts of 18:3 omega 3 or omega 3HPUFA (0.55% of the diet) did not lead to the same growth performances. 2. In the present paper, we demonstrated that fish given a high level of dietary 18:3 omega 3 (3.7% of the diet), without omega 3HPUFA, presented better growth than those offered a lower level of 18:3 omega 3, and almost the same performances as fish receiving 0.57% omega 3HPUFA. 3. This suggested that turbot, like trout, might be able to use the 18:3 omega 3 as a precursor of the omega 3 series. Furthermore, according to the present relatively short-term experiment, elongation-desaturation reactions of the omega 3FA did not appear to be reduced with low dietary omega 3FA levels. 4. On the other hand, these types of reactions seemed to be totally missing with the 18:2 omega 6. Thus, it may be assumed that there was no direct relationship between growth and omega 3 elongating-desaturating activities, and that omega 3 lowering fish body content was not the cause, or at least not the only cause, of poor growth in long-term experiments.

Utilization of shrimp meal for rainbow trout (Salmo gairdneri Rich.) pigmentation. Influence of fat content of the diet

Abstract Norwegian shrimp meal contains astaxanthin (diester 88%, monoester 12%). The total content of the pigments amounts to 25.2 mg/kg dry meal. Incorporation of this shrimp meal at 30% in rainbow trout diets with three different fat levels (9.4, 12.08, 17.4%) causes a reddish pigmentation of the skin and muscle. In the skin, astaxanthin was found in diester form, whereas this pigment was in a free form in the muscle. An increased lipid content in the diet does not seem to enhance deposition of carotenoids in the fish. Although the increase in carotenoid percentage in trout skin and muscle is important (1 mg/fish), it is relatively small compared to the large amount of pigment (25 mg/kg) contained in shrimp meal. The low fixation of carotenoids by trout is due to the poor digestibility of pigments. Since nearly 90% of the ingested pigments are found in feces, this implies that the main obstacle to carotenoids fixation is of digestive origin.

Utilization of Dietary Urea in Rainbow Trout

Experiments were conducted to examine the potential utilization of dietary urea by rainbow trout. A control diet and two diets supplemented with 1 and 3% of urea were fed to fish. Postprandial levels of urea and ammonia in blood plasma, and postprandial excretion of these metabolites were followed during 24 h. Apparent digestibility of urea in rainbow trout was very high (greater than 98%). Maximum values of urea levels in plasma were reached 6 h (32.3 +/- 10.2 micrograms/ml) after a meal in the control fish and respectively 6 h (83.4 +/- 18.4 micrograms/ml) and 8 h (250.3 +/- 96.1 micrograms/ml) after a meal in trout fed 1 and 3% urea diets. Peaks of urea excretion rates appeared 7-9 h after meal, coinciding with the highest circulating urea concentration. Total daily urea excretion amounted to 5.53, 10.43 and 33.80 mg urea N/100 mg N intake in trout fed the control, 1 and 3% urea diets, respectively. It is concluded that the dietary urea is readily absorbed in the digestive tract of trout but is totally excreted thus leading to no beneficial effect on nitrogen balance. This excretion of urea also takes place passively without any increase in energy demands.