Positive phototaxis as the cause of jaw malformations in larval greater amberjack, Seriola dumerili (Risso, 1810): Mitigation by rearing in tanks with low‐brightness walls

Abstract

Jaw malformations are a serious problem in fingerlings of the greater amberjack, Seriola dumerili. To establish a countermeasure against these malformations, we conducted a larval behavioural test to identify their root cause, and we investigated the ability of low‐brightness rearing tank walls to control their occurrence. Larval distribution was examined in a horizontally illuminated rectangular transparent aquarium (20 cm × 100 cm × 25 cm), and their distribution was biased towards the light source after this lighting was provided from 3 to 13 days post hatching (dph), indicating positive phototaxis; this response disappeared on 22 dph (there are no data between 13 and 22 dph). Larvae were observed to swim phototactically towards the light source and repeatedly collided with the tank wall (walling behaviour). To investigate the ability of wall brightness to control the incidence of jaw malformations, we compared their incidence in a rearing trial with different Munsell colour values for the tank walls: 2.11 (black), 5.85 (grey) and 9.52 (white). The incidence rate of jaw malformations at 25 dph was significantly lower in the tanks with lower‐brightness walls, that is, 5.8%, 22.5% and 26.8% for black, grey and white respectively. Larval walling behaviour was most intense for white, followed in order by grey and black. These results indicate that positive phototaxis elicits larval walling behaviour, causing jaw malformations, and that low‐brightness tank walls control this process.

Pugheadedness in Fishes

“…scombrids, carangids, clupeids, coregonids and other neritic-pelagic species held in aquaria or certain types of hatchery tanks (Suzuki et al 1973;Howey 1985;Shimizu and Takeuchi 2002;Stejskal et al 2018), can lead to a head morphology similar to pugheadedness, likely caused by collisions with walls (Blaxter and Holliday 1963). If walling happens in larval stages, it could probably cause malformations in the cranial bones and hence become actual cases of pugheadedness, as seen in Sawada et al (2020). One report of pugheadedness in laboratory-reared Pacific herring Clupea pallasii notes that the condition developed gradually through ontogeny, suggesting cumulative effects of e.g.…”

Deformities prevalence in farmed ballan wrasse (Labrus bergylta) in relation to hatchery origin and life stage

“…Equally, hatcheries operated with different coloured tanks (light blue vs. dark green), with unknown tank wall brightness characteristics, suggesting walling behaviour may have been a contributing factor to the observed difference in jaw deformity prevalence (Cobcroft et al, 2012;Sawada et al, 2020). One potential factor that has not been fully explored yet would be stocking density that is known to impact on fin condition in fish (Noble et al, 2012) and can be very variable in ballan wrasse hatcheries depending on stock survival rates.…”

The effect of different co‐feeding protocols on greater amberjack (Seriola dumerili, Risso 1810) larvae

“…In many fish species, skeletal anomalies have been frequently reported in larval culture, being often associated with a low survival of the fish larvae Izquierdo et al, 2010;Mesa-Rodriguez et al, 2019;Roo et al, 2009Roo et al, , 2019. Greater amberjack larvae are particularly susceptible to the incidence of skeletal anomalies (Roo et al, 2019;Sawada et al, 2020). Despite the predominant number of anomalies in the pre-haemal and haemal vertebrae in all larvae, greater amberjack fed low Artemia sp.…”