Allometric growth and development of organs in ballan wrasse (Labrus bergylta Ascanius, 1767) larvae in relation to different live prey diets and growth rates

Abstract

Small fish larvae grow allometrically, but little is known about how this growth pattern may be affected by different growth rates and early diet quality. The present study investigates how different growth rates, caused by start-feeding with copepods or rotifers the first 30 days post-hatch (dph), affect allometric growth and development of nine major organs in ballan wrasse (Labrus bergylta) larvae up to experimental end at 60 dph. Feeding with cultivated copepod nauplii led to both increased larval somatic growth and faster development and growth of organ systems than feeding with rotifers. Of the organs studied, the digestive and respiratory organs increased the most in size between 4 and 8 dph, having a daily specific growth rate (SGR) between 30 and 40% in larvae fed copepods compared with 20% or less for rotifer-fed larvae. Muscle growth was prioritised from flexion stage and onwards, with a daily SGR close to 30% between 21 and 33 dph regardless of treatment. All larvae demonstrated a positive linear correlation between larval standard length (SL) and increase in total tissue volume, and no difference in allometric growth pattern was found between the larval treatments. A change from positive allometric to isometric growth was observed at a SL close to 6.0 mm, a sign associated with the start of metamorphosis. This was also where the larvae reached postflexion stage, and was accompanied by a change in growth pattern for most of the major organ systems. The first sign of a developing hepatopancreas was, however, first observed in the largest larva (17.4 mm SL, 55 dph), indicating that the metamorphosis in ballan wrasse is a gradual process lasting from 6.0 to at least 15-17 mm SL.

Developmental stages of the ballan wrasse from first feeding through metamorphosis: Cranial ossification and the digestive system

“…The overall ontogeny of the digestive system in ballan wrasse larvae and juveniles observed in this study compares well with previous studies of the digestive system in ballan wrasse (Dunaevskaya, 2012 ; Gagnat et al, 2016 ; Piccinetti et al, 2017 ) and other marine teleosts (Gisbert et al, 2004 , Falk‐Petersen, 2005 , Sala et al, 2005 , Kamisaka & Rønnestad, 2011 , Gomes et al, 2014 ). The esophagus represents the transition from the mouth to the intestine and is derived from the anterior foregut (Govoni et al, 1986 ).…”

“…As the stomach and pyloric caeca form in these species, the pancreatic tissue form in‐between the caeca and the liver has the appearance as a defined organ (Mumford et al, 2007 ; Sánchez‐Amaya et al, 2007 ). In agastric species the pancreatic tissue form along the intestine after the metamorphosis (Al‐Hussaini, 1949 ; Gagnat et al, 2016 ; Kjørsvik et al, 2014 ). Gagnat et al ( 2016 ) proposed that the development of the hepatopancreas occurred concurrently with metamorphosis in ballan wrasse.…”

Isometric growth in the world's largest bony fishes (genus Mola)? Morphological insights from fisheries bycatch data

“…The estimated slope of the mass/total length linear model classes the relationship as on the borderline between isometric and allometric growth (b = 3.09). However, following similar reporting mechanisms in the recent literature (Gagnat et al, ; Rosli & Isa, ), if we consider that the true slope of the line is somewhere between 3.01 and 3.12, with a strong correlation coefficient (0.98), we suggest that a b exponent of ~3 is highly likely, although there is some variation between individuals.…”

Assessment of the efficacy of using taurine supplements to improve growth and feed utilization of juvenile starry flounder (Platichthys stellatus) given diets based on soy-protein

“…As juvenile fish develop, the growth of some organs is prioritized and higher than other tissues. This type of growth pattern is called allometric growth ( Elin et al, 2016 ). Information on the allometric growth of different organ groups may contribute to a better understanding of whether different somatic growth rates due to diet quality affect the allometric relative growth rates of internal organs.…”