Occurrence of Eggs of Bass in Ireland

8/13/2019 Occurrence of Eggs of Bass in Ireland

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mar bioi ss U K I968) 48, 585-592Printed in Great Britain

OCCURRENCE OF EGGS OF BASSDICENTR RCHUS L BR X ON THE

SOUTHERN COASTS OF IRELAN DBy MICHAEL KENNEDY AND PATRICK FITZMAURICE

Inland Fisheries Trust, Dublin Text-figs. 1-2)

During April-June, 1967, tow-netting for bass eggs was carried out at fourplaces on the Irish coast. Small numbers of bass eggs were obtained at two ofthese places, namely the Splaugh Rock, near Greenore Point, Co. Wexford andYoughal Harbour, Co. Cork. They were taken near the surface, in water of thesalinity range 30-34 5 0 and of surface temperature range 10 5-13 2 C.The Irish material was larger than described by Bertolini 1933) from theMediterranean, but smaller than described by Jackman 1954), who hatched eggsspawned in the Plymouth Laboratory Aquarium and described the larvae.

INTRODUCTIONBass have spawned in the aquarium at Naples, and their eggs have beenfound in plankton in the Mediterranean Raffaele, 1888; Bertolini, 1933).Bass have also spawned in the aquarium at Plymouth, and their eggs and theresulting young stages have been described by Jackman 1954).Hitherto, however, the eggs of bass do not appear to have been found onthe coasts of Britain or Ireland. The only young stages recorded were 14 post

larvae from 4 to 7 5 mm long, taken in the Eddystone area in the years 1925,1926, 1931 and 1933, with dates of capture between 17 March and 4 June Russell, 1935).As part of a programme of research on the biology of bass in Irish waters,tow-netting was carried out in 1967 at the Splaugh Rock off the Wexfordcoast; at Dungarvan, Co. Waterford; at Youghal, Co. Cork; and at Baltimore,

Co. Cork Fig. 1). The Splaugh, Dungarvan and Youghal are places wherebass shoal ; that is, frequently gather in shoals to attack sand-eels, herringfry or sprats at the surface. It was felt that places where bass assemble innumbers to prey on bait fish might also be places where they spawn. Bass donot usually shoal at Baltimore, but they frequent the estuary of the Ilen Riverflowing into Baltimore in fair numbers.


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586 MICHAEL KENNEDY AND PATRICK FITZMAURICEPROPERTIES OF WATER IN WHICH EGGS OCCURRED

Small numbers of bass eggs were taken in Youghal on several occasionsbetween 8 May and I June 1967; and small numbers of bass eggs were taken onboth days (1-2 June) on which tow-netting was carried out at the SplaughRock. No bass larvae or post-larvae were taken.plaugh ock

The Splaugh Rock is a reef mile south-east of Greenore Point on the eastcoast of Co. Wexford. It is situated in an area of shoals inside the 5-fathomline. Tides are swift. Salinity determinations were as follows:

I June 19672 June 1967 Neap tides; early ebbLate flood 32'1 034 5 0

oI MILES

__ SPLAUGHROCK

i

Fig. 1. Places on the Irish coast where bass eggs were sought in 1967,

YoughalYoughal Harbour is the mouth of the estuary of the Cork Blackwater, whichis tidal to Cappoquin, 14 miles from the sea.Bass occur in large numbers in Youghal Bay, in Youghal Harbour and inthe estuary above it. They often 'shoal' in the vicinity of the Bar Rocks, inthe Bay, about a mile off the Harbour mouth; they also' shoal' in the narrowsin the harbour itself.Tides are strong in the Bay, and in the Harbour. In the Harbour, undernormal conditions of flow in the Blackwater, a surface current of brackish

water continues seawards for up to an hour after low water. Mter that, thecurrent reverses, and there is a strong run of tide up the Harbour from the seaat all depths from channel bed to surface.


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EGGS OF BASS OFF SOUTHERN IRELANDSalinity determinations were not made for all tow-net hauls, but an indication of the surface salinity pattern is given by the following determinations:

Salinitytationocation Tide0)mile from open seaNeaps; H.W.3 724 354 35t miles from open seaprings; half ebb1 10 2

ow netting resultsTable I gives details of tow-net hauls in which bass eggs occurred. The netwas 45 cm in diameter and had 25 meshes per centimetre. It was fished froma small boat either slowly stemming the tide, or anchored in the tide-way,according to conditions. Hauls series 8,9 and 13 were from the surface downto 2 m; the remaining hauls were all at the surface. Each series of hauls, with

a few exceptions, represents a total of 1-2 h actual fishing-the net being leftout for 5 min to an hour at a time, according to the abundance or scarcity ofplankton.At the Splaugh Rock, 18 pelagic fish eggs were taken in three hauls. Ofthese, six were bass eggs occurring in two hauls. At Youghal, 124 eggs weretaken in 16 hauls, including 25 bass eggs in six hauls. At Youghal, the basseggs were obtained only at stations 2 and 3 mile and It miles respectivelyfrom the open sea). None occurred in the Bay (Station I) nor at the north endof the Harbour, 3t miles from the sea (Station 4). No bass eggs occurred inhauls made during the latter part of the ebb tide.

EGGS AND LARVAE OF BASSThe bass egg taken in haul 17 at Youghal on 18May contained an advancedembryo estimated to be about 3 days old. All the other bass eggs taken atYoughal and at the Splaugh Rock were recently fertilized. They were in an

early stage of cell division and contained mostly two, sometimes three, oilglobules which had not yet fused together.Some of the eggs were preserved on capture; others were brought back tothe laboratory and hatched. The surface temperature was recorded when theeggs were obtained, and the water temperature in the laboratory was alsorecorded. However, between capture and arrival in the laboratory, the eggswere in uninsulated containers in boats, hotels and cars, so no incubationtemperature can be given,The bass eggs taken at Youghal ranged in diameter from 1 20 to 1 386 mmin diameter. When a single oil-globule was present or was formed duringdevelopment, its diameter ranged from 0 36 to 0 42 mm. An egg of 1 20 mmhad two globules 0 32 and 0 20 mm across; an egg of 1 275 mm had threeglobules measuring 0 30, 0 27 and 0 20 mm; and an egg of 1 22 mm had two


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Vl000Fish eggs

:s:emp. Larvae or post-larvaeatetationide0C)assthers (nos. in parentheses) (nos. in parentheses))::r:: :tI1 8 Mayprings, flood0 5Phrynorhombus regius I) Semi-metamorphosed--l N :s:June Neaps, early ebbRocklings (2); Trachinus viperaallionymus sp (5)c :-0- ) 2 June-ate flood]12ocklings (5) Gadus spp. (2); Gobius spp.I1Solea solea (I); symmetrical Buglossidiumuteum I)


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EGGS OF BASS OFF SOUTHERN IRELANDglobules measuring 0 40 and 0 175 mm. The eggs taken at the Splaugh Rockranged from 1 20 to 1 30 mm in diameter.The Irish eggs were thus bigger than those from the Mediterranean 1 15to 1 16 mm diam., Bertolini, 1933); but were smaller than those from thePlymouth Aquarium, 1 26-1 51 mm diam., Jackman, 1954). They were ofsimilar size to the unfertilized eggs of bass from the Plymouth Aquariumdescribed by Holt Byrne 1898) 1 25-1 34 mm diam.). In appearance theeggs were as described by Bertolini and Jackman except for their size difference. They had a small perivitelline space, an undivided yolk, and acapsule without any special features. The oil-globules fuse together to forma single globule during development. The oil-globule is somewhat yellowish.The banding, which is a feature of the larva, is obvious in the embryo beforehatching. Eggs, which were in an early stage of development when collected,hatched in 3-4 days.

Fig. 2A shows a larva less than a day old, drawn when alive and anaesthetized at 4 p.m. on 12 May 1967. It was then 4 45 mm long. It had hatchedduring the previous night. When examined at 10 a.m. that morning, it hadmeasured 4 25 mm. It came from an egg in the size-range 1 20-1 30 mm.From Bertolini s figures and descriptions, it differs chiefly in that the colouredpigment, by reflected light, is more a brownish yellow than the clear yellowof Bertolini s specimens. By transmitted light, the coloured pigment is brown,not yellow. At lower magnifications, the combination of black and yellowbrown pigments gives a grey-green effect to the oil-globule and to the bandedareas of the body. This is a feature also of the advanced embryo.Fig. 2B shows a more advanced larva, 4 days old, drawn alive on 16 May.It probably came from a smaller egg than specimen 2A, as it measured only4 35 mm. The eyes were as yet unpigmented. The anterior vertical band onthe body, over the yolk sac, had faded out on the sides, but was representedby dark touches dorsally and ventrally. Again, at high magnifications, thecoloured pigment was brownish yellow rather than clear yellow by reflectedlight. Some of the melanophores-on the snout; anteriorly on the yolk sac;along the top of the gut and the ventral edge of the tail; at the vent; and inthe band over the vent-were still black, but the melanophores elsewherewere becoming brownish black. Some, but not all, of the melanophores wereconspicuously stellate. There was some diffused brown pigment, the colourof pale milk chocolate, on the head and about the eye. At lower magnifications,by reflected light, the pigment now appeared amber-brown where onlycoloured pigment occurred, and brown-grey rather than grey-green) wheredark and coloured pigments occurred together.

This example was less advanced than a 3-day-old specimen figured byBertolini; but this may be attributable to the water temperature fluctuatingin the laboratory during the period 12-16 May between 12 and 15 5 DC themean temperature being 13 5 dc.


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590 MICHAEL KENNEDY AND PATRICK FITZMAURICEFig, shows a larva 3 days old, drawn alive on 6 June 1967, This hatchedon 3 June, from an egg collected on Youghal on I June (hauls series 23).Structurally it was very similar to the 3-day-old larva, 4 5 mm long, figuredby Bertolini, and the arrangement of the pigment was very similar-though,

as in other Irish examples, the coloured pigment was not clear yellow. In this

~~ ~ : ~.. -ct~~ ~~ J~


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EGGS OF BASS OFF SOUTHERN IRELAND 59place as early as March in west Cork and Kerry. This would be consistentwith the capture of post-larval bass off Plymouth in mid-March Russell,1935). During the present Irish investigations, eggs were obtained during theperiod 8 May to 2 June 1967; but no doubt a more systematic samplingwould disclose their presence over a longer period of the year. The surfacetemperatures when Irish bass eggs were obtained varied between 10 5 and13 2 0c.Spawning off Ireland, and presumably in English waters also, is later thanin the Mediterranean, where it occurs from January to March. This is presumably attributable to differences in sea temperatures. No data are availablefor seasonal surface temperatures in Youghal Harbour, but sea temperaturesalong the Irish coast can be deduced from the monthly charts published byLC.E.S. Sea temperatures in the Bay of Naples from January 1957 to January1958 have been given by Hapgood 1960). Details are given in Table 2.

TABLE 2, TEMPERATURES OFF SOUTHERN IRELAND AND NAPLESRange of observedtemperaturesBay of Naples Jan, 1957-Jan, 1958) 0C)15 1-15 7 8 Jan, 1958)13 0-13 78 1957)13 48-15 38 1957)15 2-16 17 1957)17 09-18 53 1957)20 74-25 79 1957)

\Splaugh Rock July 1955Dec, 1958) 0C)9-9 57-8 57 5-9 58-9 59 7 IIII 5-12 5

Youghal July 1955Dec, 1958) 0C)9-9 57 5-8 58-9 58 5-9 5ro 5-II2 3

Range of mean temeraturesA

Jan,Feb,Mar.Apr,MayJuneThe bass eggs taken at the Splaugh Rock were in the open sea, though closeto shore and in shallow water. At Youghal, bass eggs, as already noted, were

obtained only on the flood, at high water and on the early ebb. This suggeststhat they were spawned in the Bay and were being swept into and out of themouth of the estuary by the strong tides. is possible that some eggs mightdrift into big eddies in the estuary where they would remain long enough tohatch. The possibility of spawning in the estuary itself cannot be excluded onthe basis of the limited data at present available. All that can be said withcertainty at this stage is that the bass eggs which were obtained occurred inwater of fairly high salinity.The eggs found associated with those of bass are of interest. While eggs ofrockling, which are ubiquitous, predominated, the other species most frequently represented were Phrynorhombus regius tenolabrus rupestris andTrachinus vipera-species which live in inshore waters and whose eggs areusually shed close to the shore. Eggs of species which normally spawn offshore were represented in the collections made at Y oughal and the SplaughRock only by two mackerel eggs, and one lemon sole egg.


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592 MICHAEL KENNEDY AND PATRICK FITZMAURICEThe invertebrate plankton associated with the bass eggs was essentiallyinshore in character.The difference in size between the eggs of Irish bass and Mediterraneanbass is consistent with observations on many other species-that eggs tend to

be larger in waters of lower salinity and temperature. the Bay of Naples,where the diameter of bass eggs does not exceed 1 16 mm Bertolini, 1933),or at most 1 2 mm Raffaele, 1888), the surface salinity in the early monthsof the year varies between 36 82 and 38 01 parts per thousand Hapgood,1960). The Irish bass eggs, measuring from 1 20 to 1 386 mm, were taken inwaters in the salinity range 30 0-34 5 parts per thousand.When adult bass shoal , with the gulls working over them, they arefeeding, not spawning. However, the present investigations have shown thatbass eggs are likely to be taken in places where shoaling occurs. Spawningprobably takes place in a variety of scattered situations, some of which, atleast, are in inshore waters where there are swift tides. The tides probablycreate the traffic patterns which result in bass becoming concentrated for atime in such places and may also create conditions favourable for spawning.It seems likely that some spawning takes place whenever temporary assembliesof bass occur throughout a rather long spawning season.

The authors thanks are due to their colleagues Desmond Brennan, Kevin Linnaneand Patrick Sheehy who participated in the tow-netting; to Dr Julie Fives of theZoology Department, University College, Galway, who identified the invertebrateplankton; and to Jack O Brien of Rosslare, John Casey of Dungarvan and Cecil Prattof Youghal, for their cooperation in the project.Thanks are also due to Dr Alwyne Wheeler of the British Museum, Dr J. E. Smithof the Marine Biological Association of the United Kingdom, and Dr P. Dohrn ofthe Stazione Zoologica, Naples, for their help in tracing references to the young stagesof marine fishes and to hydrographical conditions.

REFERENCESBERTOLINI,F., 1933. Serranidae; in Uove Larve e stadigiovanili di Teleostei: Fauna uFlora Golf Neapel Monogr. 38, pp. 3IO-I3.HAPGOOD,W., 1960. Hydrographic observations in the Bay of Naples Golfo diNapoli) January I957-January 1958 Station Lists). Pubbl Staz zooI Napoli;Vol. 31, pp. 337-7I.HOLT,E . W. L. BYRNE,L. W., 1898. Notes on the reproduction ofteleostean fishesin the south-western district. mar bioi Ass U K Vol. 5, pp. 333-5.JACKMAN,. A. J., 1954. The early development stages of the bass, Morone labrax L.).Proc zool Soc Lond Vol. 124, NO.3, pp. 531-4.RAFFAELE,., 1888. Le uove galleggianti e Ie larve dei Teleostei nel Golfo di Napoli.Mitt zool Stn Neap Bd. 8, pp. 1-84.RUSSELL,F. S., 1935. On the occurrence of post-larval stages of the bass Moronelabrax L.) in the Plymouth area. mar bioi Ass U K Vol. 20, pp. 71-2.

Occurrence of Eggs of Bass in Ireland

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