Adaptation mechanism of the adult zebrafish respiratory organ to endurance training

Abstract

In order to study the adaptation scope of the fish respiratory organ and the O 2 metabolism due to endurance training, we subjected adult zebrafish (Danio rerio) to endurance exercise for 5 weeks. After the training period, the swimmer group showed a significant increase in swimming performance, body weight and length. In scanning electron microscopy of the gills, the average length of centrally located primary filaments appeared significantly longer in the swimmer than in the non-trained control group (+6.1%, 1639 µm vs. 1545 µm, p=0.00043) and the average number of secondary filaments increased significantly (+7.7%, 49.27 vs. 45.73, p=9e-09). Micro-computed tomography indicated a significant increase in the gill volume (p=0.048) by 11.8% from 0.490 mm 3 to 0.549 mm 3 . The space-filling complexity dropped significantly (p=0.0088) by 8.2% from 38.8% to 35.9%., i.e. making the gills of the swimmers less compact. Respirometry after 5 weeks showed a significantly higher oxygen consumption (+30.4%, p=0.0081) of trained fish during exercise compared to controls. Scanning electron microscopy revealed different stages of new secondary filament budding, which happened at the tip of the primary lamellae. Using BrdU we could confirm that the growth of the secondary filaments took place mainly in the distal half and the tip and for primary filaments mainly at the tip. We conclude that the zebrafish respiratory organ -unlike the mammalian lung -has a high plasticity, and after endurance training increases its volume and changes its structure in order to facilitate O 2 uptake. Author summaryAdult zebrafish show an increase of their gill volume after endurance training, likely to adjust for the increased oxygen demand measured with respirometry during swimming.

Dynamics of repair and regeneration of adult zebrafish respiratory gill tissue after cryoinjury.

“…In contralateral gills, low levels of cyclinb1 were detected along the primary lamellae, at the base of secondary lamellae (Fig 4G -G'). This pattern is consistent with the expression of the proliferation markers PCNA and BrdU/idU in the zebrafish and Medaka gills [11,50,51]. At 3 and 7 dpc, many proliferating cells were detected in the cryoinjured area (Fig.…”

“…In teleost gills, cells in the apical domain of filaments proliferate to allow growth and addition of new secondary lamellae [50,51], making the location of cyclinb1 expressing cells at 21 dpc consistent with the growth of newly regenerated filaments observed at that stage (Fig. 1).…”

“…The basic development and growth of gill filaments can be reminiscent of appendages such as fins and limbs: gill filaments are protrusions which use apical growth to extend distally [50]. The tip of a zebrafish gill filament has actually been likened to a plant meristem with apical cells driving outgrowth to generate new secondary lamellae [51]. The fact that a known blastema marker, msx1b, is expressed in cryoinjured tissue also supports the theory of conserved repair mechanisms between gill filaments and fins.…”

A Miniature Intermittent-Flow Respirometry System with a 3D-Printed, Palm-Sized Zebrafish Treadmill for Measuring Rest and Activity Metabolic Rates

“…However, the conventional IFRS with a liter-sized swimming tunnel does not provide a suitable zebrafish-scaled swimming tunnel with a low water volume and proper flow velocities to precisely measure the metabolic rates at a single zebrafish level because of the small size and relatively slow swimming speeds of zebrafish. Recently, the IFRS with a milliliter-sized swimming tunnel of a glass tube from Loligo Systems ( ) have been typically used to study the swimming performance and active metabolic rates of larvae, juveniles and adult zebrafish in studies of endurance exercise [ 11 , 12 ], aerobic/hypoxic metabolism [ 13 , 14 ], and drug toxicity [ 15 , 16 ]. However, this miniature IFRS is expensive and the assembly of the whole system is also complicated and time-consuming.…”

A Reproducible Protocol to Measure the Critical Swimming Speed of Adult Zebrafish

“…Swimmill equipments. The absolute value of Ucrit measured in adult wild-type zebrafish (3)(4)(5)(6)(7)(8)(9)(10)(11)(12) months old) appears to vary by the difference of the swimmill equipments. This is probably due to the size difference of swimming chamber that generates uneven water flow between center and peripheral.…”