Gastrointestinal
pH and development of the acid digestion in larvae and early juveniles of
Sparus aurata (Pisces: Teleostei)
M. Yúfera, C. Fernández-Díaz, A. Vidaurreta,
J.B. Cara, F.J. Moyano-2004
Marine Biology, 144(5):
863-869
Abstract:
Changes in digestive pH and protease activity have
been determined throughout the transition from larvae to the juvenile stage
in Sparus aurata in rearing conditions (from 0.04 to 100 g wet
weight). Measurements of pH have been taken in the stomach and different
segments along the length of the intestine using a pH microelectrode. In
starved fish, the gastric pH ranged between 6.0 and 8.0 approximately,
except in juveniles of intermediate size (between 1.0 and 7.0 g wet
weight), which exhibited a wider pH range of 2.0–8.0. Fed fish with
digestive content showed, in general, lower pH values in the stomach. A
progressive decrease was observed from a pH range of 5.5–8.0 in the
youngest animals (0.04 g) to a pH range of 2.0–6.2 when juveniles
were approaching 1.0 g wet weight. Above this weight, the gastric pH
remained constant (between 2.0 and 6.0 approximately). The pH values in the
intestine ranged between 6.7 and 8.4. They were similar in the different
segments and weight classes examined, and there were no significant
differences between fed and starved animals. Specific acid protease activity
(units per milligram soluble protein) in fed animals increased from small
(0.04–1.0 g) to intermediate juveniles (1.0 and 7.0 g), but then
remained similar in larger juveniles. On the contrary, specific alkaline
protease activity in fed animals decreased from small to intermediate
juveniles, and then remained at a similar level in larger juveniles. The
results reflect a progressive transition during several months from alkaline
digestion in larvae with undeveloped stomachs to the acid digestion in
juveniles with fully developed stomachs. Full gastric capacity is developed
in seabream juveniles of 1 g wet weight, which represents approximately
100 days post-hatching in cultured populations. Nevertheless, in the
following 2.5 months, during which the intestine reaches the
appropriate length, juveniles still show a transitional period in the
regulatory mechanism of digestion, probably linked to the adaptation to a
different feeding habit.
(Instituto de Ciencias Marinas
de Andalucía (CSIC), Apartado Oficial, 11520 Puerto Real, Cádiz, Spain,
e-mail: manuel.yufera@icman.csic.es)