Scottish Animal Welfare Commission: welfare of cleaner fish used in the Scottish salmon industry - report

Appendix V - Biology of ballan wrasse

Ballan wrasse, Labrus bergylta Ascanius

Family Labridae, Superfamily Perciformes, Order Labriformes,

IUCN List status: Least Concern

This account is based largely on Davie et al. (2018).

Description

The Ballan wrasse has a heavy body with a large head and thick fleshy lips (Baldock and Dipper 2023). It has a single dorsal fin that runs along the body with sharp spines in the anterior part, which is usually folded close to the body. Coloration is variable ranging from mottled brown or green to reddish with a pale underside and pale spots on the fins (Baldock and Dipper 2023). The large scales have a dark edge and pale centre, which can give some fish a spotted appearance when this scale coloration is highly contrasting. There is no difference in coloration between the sexes, although larger fish tend to be males. Young fish tend to be uniform in coloration, mainly green, reddish or beige. Ballan wrasses reach up to 65 cm long, but typically they are 30-40 cm long (Baldock and Dipper 2023).

The two colour morphs and the two sexes display divergent growth curves (Villegas-Rios et al. 2013b). Males and spotted individuals reach larger mean asymptotic lengths than females and plain individuals, respectively, but grow more slowly to reach their asymptotic length. Almada et al. (2016) found no genetic differences (mtDNA and nuclear markers) between spotted and plain morphs, but Quintela et al. (2016) suggested that these two colour morphs may represent two distinct species based on 20 microsatellites. More recently, Seljestad et al. (2020) found distinct genetic differences (82 SNPs) between sympatric spotted and plain morphs in Galicia, northwest Spain, but not in Scandinavia, suggesting a more complex pattern of differentiation.

Distribution and habitat

The Ballan wrasse is found in coastal waters of the eastern Atlantic ranging from Morocco to Norway (Davie et al. 2018). Genetic analyses of mtDNA and microsatellites have identified two main genetic clades (Atlantic and Scandinavian), which probably reflect glacial refugia in the North Sea and off the western and southern Iberian coasts with an additional clade from a largely isolated refugium around the Azores (D’Arcy et al. 2013a; Almada et al. 2017). The current population structure has its origins in glacial refugia coupled with current and past oceanographic circulation patterns.

The Ballan wrasse inhabits sublittoral zones and is closely associated with rock faces, boulder slopes, offshore reefs and kelp beds up to 30 m deep (Davie et al. 2023, Burns et al. 2025). It is active only during the day, hiding in rock crevices and seaweed beds at night (Davie et al. 2018).

Ballan wrasses have very small home ranges and show high site fidelity. A study of home-range use by Ballan wrasses in the Galician Atlantic Islands Maritime-Terrestrial National Park based on 25 individuals over 71 days between September and November 2011 showed that they stayed within the monitored area 92% of the monitored time (Villegas-Rios et al. 2013b). Home ranges were very small; mean total minimum convex polygons were estimated as 0.133 ± 0.072 km2 and whereas 95% kernel distribution estimated mean home-range size as 0.091 ± 0.031 km2 (Villegas-Rios et al. 2013b). The mean core area (50% kernel) was very small: 0.019 ± 0.006 km2. Ballan wrasses showed different daily movement patterns, with most fish (92%) being more active and moving greater distances during daytime. Most fish (76%) had larger home ranges during the day compared with the night during the night and there was high site fidelity (volume of intersection index between consecutive daily home ranges was 0.75 ± 0.13) (Villegas-Rios et al. 2013b). Ballan wrasses are generally inactive at low seawater temperatures of 5-10°C (Yuen et al. 2019).

Diet and feeding

Ballan wrasses have a short gut and are agastric, and so need to feed continuously. Deady and Fives (1995) investigated the gut contents of 99 Ballan wrasses between April and July from Galway Bay, Ireland and 95 individuals between April and June from Brittany, France. Galway Bay Ballan wrasses’ diet included 19 food categories. Decapods (Cancer pagurus, Carcinus maenas and Eupagurus bernhardus) and bivalves (c.90% Mytilus edulis) were the major prey categories in both areas, but algae (Laminaria spp., Fucus spp., Ceramium rubrum and Palmaria palmata) and gastropods (Littorina spp., Calliostoma zizyphinum, Bittium reticulatum and Lacuna vincta) were eaten often but in much smaller amounts. Although the volume of major food categories did not vary significantly with fish length, wrasses more than 20 cm long ate greater volumes of bivalves than smaller fish. Dietary diversity increased during the breeding season. The Ballan wrasses from Brittany mainly ate bivalves with Chlamys spp.(c.80%) comprising most of these (Deady and Fives 1995).

There were some differences in diet between the same sexes at the two different locations. Males ate many more bivalves and preferred fish slightly more than females, but females had a more diverse diet than males, consuming more algae, amphipods, isopods and considerably more bryozoans (Deady ad Fives 1995). The males from Brittany ate fewer bivalves and more ascidians, decapods and fish than females, but dietary diversity was similar for both sexes (Deady and Fives 1995). The diets of males from each site had different diets; the males from Brittany ate more algae, ascidians and fish and fewer bivalves compared with the Galway Bay population. Females from Galway Bay consumed significantly more decapods and amphipods, whereas females from Brittany ate more ascidians and bivalves.

Cardona et al. (2020) used stable isotope analysis to compare the isotope niches of the plain and spotted morphs of the Ballan wrasse off Galicia (NW Spain). Plain morphs of Ballan wrasse always had depleted δ13C values compared to spotted morphs, whereas δ15N values of plain morphs showed that they fed at higher trophic levels than the spotted morphs in high-density unfished populations, but these differences were not apparent or were reversed in fished areas. Therefore, resource partitioning is density dependent and the two morphs have different ecological niches in unfished ecosystems (Cardrona et al. 2020).

Le et al. (2019) have described the digestion, absorption and evacuation rates of captive juvenile Ballan wrasse fed dry or pre-soaked diets with inert markers. Evacuation of the digestive tract was completed by 12-14 hours after feeding for both kinds of dietary hydration. Ninety percent of the digesta moved from the foregut to the midgut after 4-8 hours and 7% was found in the hindgut after four hours. The major site of digestion was the foregut, where most carbohydrates (86%), proteins (74%), and lipids (50%) were absorbed (Le et al. 2019). Absorption of proteins (90%), carbohydrates (98%) and lipids (80%) increased until the hindgut.

Reproduction

The Ballan wrasse is a monandric protogynous hermaphrodite with a harem mating system and a highly skewed sex ratio of c.10% males in the wild (Grant et al. 2016). All Ballan wrasses hatch as females and protogynous sex change of some females to males is thought to driven by mostly unknown social cues (possibly size and/or social dominance) from about 5-6 years old and when they are more than 28 cm long (Grant et al. 2016). In northern Europe 50% sex change occurs at 10.8 years with a weight of 636 g and length of 342 mm (Davie et al. 2018).

Male Ballan wrasses are highly territorial during the spawning season, defending areas of up to 300 m2, which is a small proportion of the estimated home-range size (see above) (Davie et al.2018). The males guard active nest sites, which restricts the spawning season. It has been suggested that there is a latitudinal cline in spawning season, but this has not been confirmed (Davie et al. 2018).

Based on histology, Ballan wrasses are classified as a group-synchronous multiple-batch spawning species, with the breeding season occurring between April and July (mean 58.5±4.8 days) and varying geographically (Muncaster et al., 2013). In captivity there are 3-5 spawning periods, lasting 1-6 days including spawning, with an inter-spawning interval 8-15 days and 4-6 spawning windows over the season. This regular pattern of spawning suggests a “multiple or repetitive spawning” reproductive strategy (Grant et al. 2016).

Fertilisation rates are very high in captivity (>87.5%), but hatch rates are very variable (0-97.5%), peaking in the middle of the spawning season. A captive study showed that 50% of six spawnings involved single parents, while the other 50% involved more than a pair of parents, including a male with two females and a female with fertilisations by two males (Grant et al. 2016). D’Arcy et al. (2012) identified eight primary embryonic developmental stages of the eggs. Ballan wrasses have a short egg stage, hatching occurring c.123 hours (or 62.5 degree days) after fertilisation at 12.2±1.1oC; the larvae swim intermittently near the surface of the water column (D’Arcy et al. 2012). Young fish grow fastest and are more robust and active in the winter. Larval growth factors have been studied by Piccinetti et al. (2017) and larval organ growth in captivity by Gaagnat et al. (2016). Ballan wrasses grow slowly and are long-lived, reaching a maximum length of 65.9 cm and weight of 4.35 kg during a 29-year lifespan (Davie et al. 2023).The oldest known Ballan wrasse was a 34-year-old female caught off the coast of western Norway (Pritchard et al. 2024).

References

Almada, F., Casas, L., Francisco, S.M., Villegas-Ríos, D., Saborido-Rey, F., Irigoien, X. and Robalo, J.I. (2016). On the absence of genetic differentiation between morphotypes of the ballan wrasse Labrus bergylta (Labridae). Marine Biology 163(4): 86.

Almada, F., Francisco, S.M., Lima, C.S., FitzGerald, R., Mirimin, L., Villegas-Ríos, D., Saborido-Rey, F., Afonso, P., Morato, T., Bexiga, S. and Robalo, J.I. (2017). Historical gene flow constraints in a northeastern Atlantic fish: phylogeography of the ballan wrasse Labrus bergylta across its distribution range. Royal Society Open Science 4(2): 160773.

Baldock, L. and Dipper, F. (2023). Inshore fishes of Britain and Ireland. Princeton University Press, New Jersey and Oxford.

Barrett, L.T., Oppedal, F., Robinson, N., Dempster, T. (2020). Prevention not cure: a review of methods to avoid sea lice infestations in salmon aquaculture. Reviews in Aquaculture (2020) 12, 2527–2543.

Burns, N.M., Hopkins C.R. and Bailey D.M. (2025). Assessing the implications of wrasse fishing for marine sites and features. NatureScot Commissioned Report No. RR1207.

Cardona, L., Reñones, O., Gouragine, A., Saporiti, F., Aguilar, A. and Moranta, J. (2020). Fishing alters resource partitioning between colour morphs in a temperate coastal fish. Marine Ecology Progress Series 648: 179-190.

D’Arcy, J.D., Dunaevskaya, E., Treasurer, J.W., Ottesen, O., Maguire, J., Zhuravleva, N., Karlsen, A., Rebours, C. and FitzGerald, R.D. (2012). Embryonic development in ballan wrasse Labrus bergylta. Journal of Fish Biology 81: 1101-1110.

D'Arcy, J., Mirimin, L. and FitzGerald, R. (2013). Phylogeographic structure of a protogynous hermaphrodite species, the ballan wrasse Labrus bergylta, in Ireland, Scotland, and Norway, using mitochondrial DNA sequence data. ICES Journal of Marine Science 70(3): 685-693.

Davie, A., Grant, B., Clark, W. and Migaud, H. (2018). The Ballan wrasse (Labrus bergylta) reproductive physiology, broodstock management and spawning behaviour. In: Treasurer , J. (ed.).Cleaner Fish Biology and Aquaculture Applications, pp. 26-36. CABI, Wallingford.

Deady, S. and Fives, J.M. (1996). Diet of ballan wrasse, Labrus bergylta, and some comparisons with the diet of corkwing wrasse, Crenilabrus melops. Oceanographic Literature Review 2(43): 176.

Gagnat, M.R., Wold, P.A., Bardal, T., Øie, G. and Kjørsvik, E. (2016). Allometric growth and development of organs in ballan wrasse (Labrus bergylta Ascanius, 1767) larvae in relation to different live prey diets and growth rates. Biology Open 5(9): 1241-1251.

Grant, B., Davie, A., Taggart, J.B., Selly, S.L., Picchi, N., Bradley, C., Prodohl, P., Leclercq, E. and Migaud, H. (2016). Seasonal changes in broodstock spawning performance and egg quality in ballan wrasse (Labrus bergylta). Aquaculture 464: 505-514.

Hall. L.M., Smith, R.J., Munro, E.S., Matejusova, I., Allan, C.E.T., Murray, A. G., Duguid, S. J., Salama, N.. K G., McBeath, A. J. A., Wallace, I. S., Bain, N., Marcos-Lopez, M. and Raynard R. S.. (2013). Epidemiology and Control of an Outbreak of Viral Haemorrhagic Septicaemia in Wrasse Around Shetland Commencing 2012. Scottish Marine and Freshwater Science 4(3). Published by Marine Scotland – Science ISSN: 2043-7722

Le, H.T., Shao, X., Krogdahl, Å., Kortner, T.M., Lein, I., Kousoulaki, K., Lie, K.K. and Sæle, Ø. (2019). Intestinal function of the stomachless fish, ballan wrasse (Labrus bergylta). Frontiers in Marine Science 6: 140.

Palma, P.A., Lwin, S.S., Jimenez-Fernandez, E., Perschthaler, J.H., Baily, J.L. and Gutierrez, A.P. (2023). Insights into the early gonad development of the protogynous ballan wrasse (Labrus bergylta). Aquaculture Reports 33: 101857.

Piccinetti, C.C., Grasso, L., Maradonna, F., Radaelli, G., Ballarin, C., Chemello, G., Evjemo, J.O., Carnevali, O. and Olivotto, I., 2017. Growth and stress factors in ballan wrasse (Labrus bergylta) larval development. Aquaculture Research 48(5): 2567-2580.

Pritchard, C.J., Stendal, M.M., Treasurer, J., Halvorsen, K.T. and Skiftesvik, A.B. (2024). A new maximum age observed within the family Labridae, ballan wrasse Labrus bergylta. Journal of Fish Biology 105(4): 1354-1356.

Quintela, M., Danielsen, E.A., Lopez, L., Barreiro, R., Svåsand, T., Knutsen, H., Skiftesvik, A.B. and Glover, K.A. (2016). Is the ballan wrasse (Labrus bergylta) two species? Genetic analysis reveals within‐species divergence associated with plain and spotted morphotype frequencies. Integrative Zoology 11(2): 162-172.

Seljestad, G.W., Quintela, M., Faust, E., Halvorsen, K.T., Besnier, F., Jansson, E., Dahle, G., Knutsen, H., André, C., Folkvord, A. and Glover, K.A. (2020). “A cleaner break”: genetic divergence between geographic groups and sympatric phenotypes revealed in ballan wrasse (Labrus bergylta). Ecology and Evolution 10(12): 6120-6135.

Treasurer, J. (2018). An introduction to sea lice and the rise of cleaner fish. In: Cleaner Fish Biology and Aquaculture Applications. Ed: J. Treasurer. 5M Publishing Ltd. Sheffield, England

Villegas-Ríos, D., Alonso-Fernández, A., Fabeiro, M., Bañón, R. and Saborido-Rey, F. (2013a). Demographic variation between colour patterns in a temperate protogynous hermaphrodite, the ballan wrasse Labrus bergylta. PLoS One 8(8): e71591.

Villegas-Ríos, D., Alós, J., March, D., Palmer, M., Mucientes, G. and Saborido-Rey, F. (2013b). Home range and diel behavior of the ballan wrasse, Labrus bergylta, determined by acoustic telemetry. Journal of Sea Research 80: 61-71.