Swim bladder morphology changes with female reproductive state in the mouth-brooding African cichlid Astatotilapia burtoni

Abstract

Mouth brooding is an extreme form of parental care in which the brooding parent carries the developing young in their buccal cavity for the duration of development. Brooding fish need to compensate for the brood weight on the anterior portion of their body. For fishes with a compartmentalized swim bladder, gas distribution between the chambers may aid in regulating buoyancy during brooding. To test this hypothesis, we took radiographs of to compare the swim bladder morphology of gravid, mouth-brooding and recovering females. Following spawning, females carry developing fish in their buccal cavity for ∼2 weeks, resulting in a larger and rounder anterior swim bladder compartment. Comparatively, the swim bladder of gravid females is long and cylindrical. Using small beads to mimic brood weight and its effects on female buoyancy, swim bladder changes were induced that resembled those observed during brooding. Immediately after releasing their fry, brooding females swim at a positive angle of attack but correct their swimming posture to normal within 5 min, suggesting a rapid change in swim bladder gas distribution. These data provide new insights into how swim bladder morphology and swimming behavior change during mouth brooding, and suggest a compartmentalized swim bladder may be a morphological adaptation for mouth brooding.

Noise during mouthbrooding impairs maternal care behaviors and juvenile development and alters brain transcriptomes in the African cichlid fishAstatotilapia burtoni

“…A second group of control fish were placed in the experimental setup but without a sound file selected (ambient sound levels just above the spawning shelter: ~90 dB re: 1 μPa). While A. burtoni likely responds primarily to the particle acceleration component of sound, short anterior projections of the swim bladder suggest that they may also respond to sound pressure but this requires further experimental study 29 . We used a total of 32 females: 10 per group in behavior experiments, and 6 per group for brain and hormone data.…”

The relationship between target strength frequency response and vertical swim velocity: a new approach for fish discrimination

“…Carp have two-chambered "physostomous" swimbladder, which is connected to gut (e.g., Grom, 2015). Tilapias have two-chambered "physoclistous" (closed) swimbladders (e.g., Butler et al, 2017). Mullet have one-chambered physoclistous swimbladder (e.g., Moore, 1970).…”

Sex and male breeding state predict intraspecific trait variation in mouth‐brooding fishes

“…Nonetheless, whether mouth‐brooding leads to other morphological differences ( e.g ., morphological or functional traits) as well as performance trade‐offs in the adult carer is still largely speculative (but see Tkint et al ., 2012; Van Wassenbergh et al ., 2015). Some studies have also suggested that the adult mouth‐brooding carer can undergo temporary internal and external trait changes only while incubating eggs ( e.g ., Butler et al ., 2017; Okuda et al ., 2002; Van Wassenbergh et al ., 2015). In the paternal mouth‐brooding cardinalfish Apogon doederleini (Jordan and Snyder 1901), males differ from females in the morphometric measures of the head‐jaw region, including the buccal cavity, during the breeding period but not in the non‐breeding season (Okuda et al ., 2002).…”