Vertebral, Scale and Otolith Characteristics of Senile Kahawai, Arripis Trutta: Implications for Age Estimation

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<ul><li><p>Vertebral, scale and otolith characteristics ofsenile kahawai, Arripis trutta: implications forage estimation</p><p>R.W. Gauldie</p><p>76 Inglis Street, Seatoun, Wellington, New Zealand</p><p>Specimens of New Zealand kahawai (Arripis trutta; Bloch and Schneider) reared in theNational Aquarium of New Zealand (NANZ) from 12 year old sh in 1975 to the presentshowed outward signs of senility and were large (.75 cm fork length (FL)) compared withA. trutta in the wild, which usually have a maximum size of .60 cm FL. One of the NANZsh died on 12 April 1997 and a second sh was killed and both were then examined bycomputerized axial tomography (CAT) for vertebral anomalies and otolith location. Twoyounger NANZ specimens in the .48 cm FL size range were also killed and CAT scannedfor comparison, as were three specimens of orange roughy (Hoplostethus atlanticus;Collette). The patterns of incremental scale growth of the aquarium sh were comparedwith that of scales from an unusually large (75.4 cm FL) wild specimen of A. trutta from theMuseum of New Zealand collection.</p><p>KEYWORDS: Arripis trutta, CAT scan, Hoplostethus atlanticus, otoliths, scales, senility,vertebrae</p><p>INTRODUCTION</p><p>The physiological consequences of age in sh that involve deterioration offunction in one or more organs result in an increased risk of predation. For somelarger species, size alone may deter predation so that survival with signicantphysiological senility may occur. However, for small or moderate-sized sh (,1 m)the physiological dysfunction associated with senility would be expected to leadto increased predation mortalities. Thus, physiologically senile sh can beexpected to be hard to nd in the wild. Aquaria have an important role inproviding predator-free healthy environments within which sh can live to theirbiologically maximum age and die from natural causes. Such sh provide valuablebenchmarks in assessing techniques of age estimation in sh. The NationalAquarium of New Zealand (NANZ) has been particularly successful in maintainingits sh in peak health resulting in many specimens living far beyond the age (andsize) that they might be expected to reach in the wild.</p><p>This paper describes the vertebral and scale characteristics as well as the insitu positioning of otoliths of two senile specimens of kahawai, Arripis trutta(Bloch and Schneider), from the NANZ. The teleost family Arripidae (Percom-orpha) comprises a single genus with three species (Paulin, 1993) in temperateAustralian and New Zealand waters. Arripis trutta occurs in the coastal waters of</p><p>Aquarium Sciences and Conservation, 2, 5366 (1998)</p><p>13575325 # 1998 Chapman &amp; Hall</p></li><li><p>New Zealand, Chatham Island (Roberts, 1991), the Kermadec Islands, Norfolk andLord Howe Islands (Francis, 1991), New South Wales and Tasmania. There isconsiderable movement of tagged A. trutta around New Zealand (Wood et al.,1990) and the New Zealand population is regarded as a single stock of sh(Kilner, 1988). Three specimens of orange roughy Hoplostethus atlanticus: Colette(Trachichthyidae) were available and were also examined for vertebral charac-teristics. Hoplostethus atlanticus has been described as a very long-lived sh of.150 years maximum age (Smith et al., 1995). Although those extreme ages arenow in doubt (West and Gauldie, 1994; Romanek and Gauldie, 1996; Whiteheadand Ditchburn, 1996) it was nonetheless of interest to compare their vertebralcharacteristics with sh known to be physiologically senile at an apparentlymuch younger age.</p><p>Arripis trutta is a hardly aquarium sh. Twenty-two small A. trutta ofapproximately 25 cm total length (TL), 12 years old by conventional annualageing (Nicholls, 1973; Eggleston, 1975; Wood et al., 1990), were placed in theNANZ in 1975. The mortalities in this group of sh have been low. By 1987, 12specimens remained, one of which died of old age in that year and wasrecovered from the tank with little damage and frozen. Similarly, a second shdied of similar symptoms in 1989 and was also recovered intact and frozen. Thedetails of the otoliths and scales of these two specimens were described inGauldie et al. (1993).</p><p>Mortalities occur at night and by morning the dead specimens are usually sobadly damaged by other sh in the tanks that the specimens are not worthfurther study. However, by 1997 four of the original A. trutta remained alive, oneof which died on 12 April 1997 and was recovered undamaged and frozen. It wasdecided to examine this specimen in more detail including visualization of theinternal hard parts using computerized axial tomography (CAT) scans. Aprevious study using magnetic resonance imaging (MRI) of whole live shproved a valuable source of information about the internal soft and hard parts ofsh (Seri et al., 1995). The remaining three specimens showed a number ofabnormalities particularly in swimming and it was decided to kill one of thesesh to allow examination of a fresh specimen. This paper describes the vertebraland scale characteristics of the two large NANZ specimens of A. trutta. Twoyounger specimens of A. trutta and three specimens of H. atlanticus from theNANZ were examined for comparison. In addition, the scales from an unusuallylarge wild specimen of A. trutta from the collection of the Museum of NewZealand were also examined.</p><p>MATERIALS AND METHODS</p><p>Captive sh</p><p>The fork lengths (FLs) of the two large NANZ specimens of A. trutta were 75.4 and76 cm, respectively. They were conrmed as A. trutta from the key provided inPaulin (1993). The frozen dead specimen was allowed to thaw and placed in 12%buffered formalin. The second specimen was recovered from the aquarium using anet and killed and placed in 12% buffered formaldehyde. At the same time, two</p><p>54 R. W. Gauldie</p></li><li><p>younger specimens of A. trutta (48.3 and 49.4 cm FL, respectively) from aquariumtanks were also killed and placed in formalin.</p><p>A sample of ten scales was taken from each sh posterior to the tip of thepectoral n in the area of the lateral line canal. Scales from this region have beenshown to have the least errors associated with scale reading (Dannevig and Host,1931). The scale annuli were counted using the method of Eggleston (1975).</p><p>Wild sh</p><p>On 14 July 1997 a 75.4 cm FL specimen of A. trutta was caught in the commercialshery in the Bay of Plenty and donated to the National Museum of New Zealand(MONZ) collection (NMNZ p. 34778). A sample of ve scales from the post-pectoraln region was made available for this study by the keeper of the NMNZ shcollection.</p><p>CAT scanning</p><p>The formalin container was a cylinder made of low-density polyethylene, 79 cmhigh and 48 cm wide, holding 120 l with a tightly tting lid. Once sealed thecontainer was passed through a General Electric computerized axial tomography(CAT) scanner at the Wakeeld Hospital in Wellington, New Zealand. Thespecimens were CAT scanned less than 12 h after being placed in formalin. Scanswere made at 5 mm intervals. However, a shorter series of ten scans at 1 mmintervals was made to provide a detailed image of a small section of the spine ofthe 76 cm FL, NANZ A. trutta. The CAT scan data were analysed using the GeneralElectric Three Dimensional Reconstruction software package on a Sun work-station. Images were printed on a Color Transfer E7014LA photographic printer.</p><p>Scales</p><p>The scales were inserted into a photographic enlarger and the subsequent imageexposed on photographic paper as if the scale were a negative. Data analysis wascarried out using Data Desk software.</p><p>Otoliths</p><p>The otoliths were cut in half in the vertical plane (i.e. the mediolateral plane insitu) and sections mounted with epoxy resin on stainless steel pin mounts. Half ofthe otolith was mounted on a glass slide and ground down to provide a thin(50 m) optical section using 4000 grit wet and dry paper on a petrographicgrinder.</p><p>Water temperature records</p><p>Temperature and salinity records from December 1978 to June 1997 were obtainedfrom the daily records maintained by the NANZ (R. Yarrell, personal communica-tion).</p><p>Vertebral, scale and otolith characteristics of A. trutta 55</p></li><li><p>RESULTS</p><p>Senility</p><p>Similarly to previously examined specimens (Gauldie et al., 1993), the two large A.trutta specimens from the NANZ had advanced locomotor dysfunction involvingexcessive rolling in the water and swimming head downwards or with a pitchingmotion, as well as whitening of the body colour and both exophthalmia and mildcataract in the eyes. These are all indications of senility in sh (Gerking, 1959;Comfort, 1961; Liu and Walford, 1969).</p><p>On the morning of 12 April 1997 the rst large specimen from the NANZ wasfound dead at the bottom of the main tank. The sh was measured as 75.4 cm FL.An autopsy showed that it was a male in good condition but with atrophiedgonads and with no obvious signs of internal disease, parasites or internallesions. The second NANZ sh was killed on 6 June 1997. The sh was measuredas 76 cm FL. An autopsy showed it to be a female in good condition but withreduced gonads and with no obvious signs of internal disease, parasites orinternal lesions. In both sh the spinal vertebrae were fused together into a rigidmass with the characteristic `bamboo' appearance (Fig. 1a, and b) of vertebralankylosing osteoarthritis in humans. It was concluded that both sh had died ofold age.</p><p>A short series of ten CAT scans at 1 mm intervals revealed the detailedstructure of the spinal column of the 76 cm FL NANZ sh which is shown in Fig.2a. The base of the neural spine at the top of the vertebrae arches backwards (asin Fig. 1b) and is lost in this section. The transverse processes of the vertebraepass backwards and are fairly short. The haemal spine passes downwards andbackwards. Although the foramen of the spinal nerve and the spinal cord areplainly visible, the gap in the two neural processes that form the neural spines isnot visible. The whole vertebrae have become so ossied that the normallyvisible surface sculpturing of the vertebrae is lost obscuring the fusion of thehaemal and neural processes into the haemal and neural spines. In addition, theossied surface shows the lumpy surface typical of osteophytes associated withosteoarthritis.</p><p>The CAT scans of both of the large NANZ specimens of A. trutta were ofsections taken at 19 and 20.5 cm from the anterior of the sh, respectively (Fig.2b). Both sh showed the small dark gas-lled vesicles within the spinal uidthat are indicators of changes typical of senile degeneration of the spinal columnin humans. Gas-lled vesicles were not observed in the vertebrae of either of thesmaller specimens of A. trutta or the specimens of H. atlanticus.</p><p>Water temperature records</p><p>The mean annual water temperatures are shown in Fig. 3a plotted against time.Water is drawn directly from Hawkes Bay into the NANZ and ltered beforecirculation. The temperatures track the local environment temperatures. Themean monthly temperatures are shown as a histogram inserted into Fig. 3a. Themean summerwinter differential is approximately 5.6 8C.</p><p>56 R. W. Gauldie</p></li><li><p>Fig. 1. Three-dimensional reconstructions of the spines of (a) the 75.4 cm FL NANZ and (b)the 76 cm FL NANZ A. trutta showing the characteristic bamboo appearance of ankylosingosteoarthritis. The scale bars are 5 cm.</p><p>Vertebral, scale and otolith characteristics of A. trutta 57</p></li><li><p>Age estimationScales</p><p>Both of the NANZ specimens of A. trutta showed clear checks in their scales of thekind conventionally used in sh ageing (Kelley, 1988), including those gured by</p><p>Fig. 2. (a) Three-dimensional reconstruction of a vertebra from the spine of the 76 cmFL NANZ A. trutta. The neural (N) and haemal (H) spines are indicated with arrows.The transverse process (T) of the vertebra passes backwards and out of the scan.The foramen of the spinal cord (SC) and the spinal nerve (SN) are indicated witharrows. Irregular osteophytes (O) on the surface are indicated with arrows. The bar is5 mm.</p><p>58 R. W. Gauldie</p></li><li><p>both Eggleston (1975) and Gauldie et al. (1993). Approximately 70% of the scalesdid not show a clear sequence of checks and appear to correspond to the type ofscales described as `erosion' or `replacement' scales, but were in signicantlygreater proportions than those found in old sh of other species (Paget, 1920) aswell as A. trutta (Gauldie et al., 1993).</p><p>The year in which the 76 cm FL NANZ sh was spawned, as projected byageing one of the scales, was 1973. Both the otolith and scale ages predict that a25 cm sh would be between 1 and 2 years old (Eggleston, 1975). As the sh wascaught in 1975, the scale-based date agrees well with a 1973 projected date ofspawning. However, the other two readable scales from the same sh gave agesof 17 and 19 years, respectively. The true birth date of this group of senile A.trutta was likely to be 1973 making these sh 24 years old at death. Only twoscales from the sample of ten scales taken from the second sh showed clearchecks. One scale was counted as having 24 checks and the other 18 checks.</p><p>Fig. 2. (b) The sections of the 75.4 cm FL NANZ sh (left-hand side) and the 76 cmFL NANZ sh (right-hand side) show gas-lled vesicles within the spinal cord (shortarrows). Other gas-lled inclusions as well as the gas bladder can be seen in theabdominal cavity including that of the 49.4 cm FL NANZ A. trutta at the bottom of thegure.</p><p>Vertebral, scale and otolith characteristics of A. trutta 59</p></li><li><p>Counting the scale annuli using the method of Eggleston (1975) yielded an ageof .9 years for the 48.3 cm FL NANZ specimen and .10 years for the 49.4 cm FLNANZ specimen.</p><p>The scales from the 76 cm SL specimen from the NMNZ were aged using themethod of Eggleston (1975), giving ages of .14 years from two of the scales and.13 years from the third.</p><p>The cumulative incremental growth of the scales from the 48.3 cm NANZ, 76 cmNANZ and 75.4 cm MONZ specimens, respectively, are shown in Fig. 3b. Thescales of the 76 cm NANZ sh grew more slowly than those of the 48.3 cm NANZand 75.4 cm MONZ sh. The scales of the 48.3 cm NANZ and 75.4 cm MONZ shgrew at similar rates over the rst nine annual increments. The regression of the</p><p>Fig. 3. (a) Annual scale increment deviation (d) back calculated from the year ofdeath and mean water temperature deviation (j) plotted against year with an insertedhistogram of the mean monthly (JanuaryDecember, 112) temperatures (8C). (b)The cumulative scale increment growth is plotted against years for the 48.3 cm NANZsh (+), the 75.4 cm MONZ sh (3) and the 76 cm NANZ sh (s).</p><p>2 6 10</p><p>4</p><p>12</p><p>20 a</p><p>1980 1984 1988 1992Year</p><p>21</p><p>0</p><p>1</p><p>2Te</p><p>mpe</p><p>ratu</p><p>re (fi</p><p>lled s</p><p>quare</p><p>s) an</p><p>d cum</p><p>ulativ</p><p>e sca</p><p>legr</p><p>owth</p><p> (fille</p><p>d circ</p><p>les) d</p><p>eviat</p><p>ions</p><p>b</p><p>1 3 5 7 9 11 13 15 17 19 21 23 25Annual increment number</p><p>4</p><p>8</p><p>12</p><p>16</p><p>20</p><p>Cum</p><p>ulat</p><p>ive g</p><p>rowt</p><p>h m</p><p>m</p><p>60 R. W. Gauldie</p></li><li><p>cumulative scale growth of the 48.3 cm NANZ sh on the equivalent growth ofthe 75.4 cm MONZ sh showed a strong correlation (r2 98:2%).</p><p>The previous study of Gauldie et al. (1993) showed similarities between thepattern of scale growth measured as annual growth increment widths comparedwith the mean annual temperature recorded in the aquarium....</p></li></ul>

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