Cybium, Revue Internationale d’Ichtyologie
Copyright © 2002 Société Française d’Ichtyologie

(1) Aquaculture and Ichthyology Consulting, 3 Plan de la Croix, 34980 Montferrier-sur-Lez, FRANCE.
(2) UR Ressources Ichtyologiques en Plan d’Eau, CEMAGREF/GAMET, BP 5095-34033 Montpellier, FRANCE.

Résumé. - La détermination de certains paramètres hématologiques de base en élevage intensif de Silurus glanis a été effectuée sur 143 juvéniles de l’espèce (poids compris entre 55 et 250 g et d’une LT entre 19 et 31 cm). Les paramètres explorés étaient : natrémie, kaliémie, chlorémie, osmolarité, glucose, hématocrite, leucocrite et lysozyme plasmatique. À l’exception de la natrémie, de la chlorémie et de l’osmolarité, tous les autres paramètres ont montré une forte variabilité individuelle, en particulier la kaliémie, le rapport K/Na, le leucocrite et le lysozyme plasmatique. Des corrélations significatives sont présentes entre natrémie, osmolarité, lysozyme plasmatique et hématocrite. Les analyses comparatives intragroupe suggèrent que le poids puisse influencer l’hématocrite, le lysozyme plasmatique et l’osmolarité. La possibilité que les variables hématologiques puissent varier en fonction de l’origine des poissons est discutée.

Abstract. - Haematological baseline values of juvenile Silurus glanis (Siluridae) reared in intensive conditions.

The non availability of haematological baseline values could be one of the reasons why health fish monitoring according to their haematological parameters is not a current practise. This is especially true for the sheatfish (Silurus glanis), for which the baseline values are unknown. The aim of this paper was to present the results from three observation series carried out on juvenile sheatfish in order to determine the plasmatic baseline values of Na⁺, K⁺, Cl^-, glucose, osmolarity, haematocrite, leucocrite and lysozyme. The morphological characteristics of the fish (size, length and condition factor) as well as their geographic origin were evaluated as possible factors of variability in the baseline values.
The three series of observations were carried out on 70, 50 and 36 juvenile sheatfish, respectively in the first second and third experiment (weight and total length range from 55 to 250 g and from 19 to 31 cm). Fish were reared into a close warm water system (26-27°C), in shallow light (approx. 0.644 W/m²) and fed at 1% of their biomass per day during more than 3 weeks before sampling procedures. After individual catch, fish were immediately sacrificed and 1 ml of blood was collected with heparinized syringes. The determination of Na⁺, K⁺ and Cl^- was performed using a spectrophotometer; plasmatic lysozyme was also determined by spectrophotometry according to Parry’s method (Ellis, 1990). The haematocrite and leucocrite values were obtained with “Compur microspin” (3000 laps/min for 6 min) and glucose was determined using a glucometer (Bayer Diagnostic)
In juvenile sheatfish, the baseline values of selected blood parameters were as follows (data are expressed as an average ± IC at 95%): natremia 128 ± 1.210 mEq/l; plasma chloride 111 ± 1.562 mEq/l; K⁺ 3 ± 0.275 mEq/l; osmolarity 238 ± 1.981 mOsm/l; glucose 43 ± 2.673 mg/l; K/Na rate 0.023 ± 0.002; haematocrite 25 ± 0.928%; leucocrite 0.94 ± 0.076% and plasma lysozyme 337 ± 16.655 U/ml.
Except for the first three blood parameters, all the other parameters showed high individual variability as attested by the high coefficient of variation. Significant correlation existed between the plasma osmolarity haematocrite and the lysozyme, and the statistical analysis suggested that weight value was positively related to these parameters. The same parameters plus the natremia allowed to differentiate the three groups of fish according to the two different geographic origins with a significant chi-squared value of discriminant analysis
Potential factors, which could be responsible for the variations of baselines, were discussed. The individual variability seemed to be the most probable cause of variability but the weight and the geographic origin (probably a different genetical origin) were also implicated in the variation of some haematological parameters of the sheatfish.

Key words. - Siluridae - Silurus glanis - Blood baseline values - Stress.