Some morphometric measurements of juvenile rainbow trout (Oncorhynchus mykiss) and inanga (Galaxias maculatus) relevant to fish passage remediation

Linear regression analysis between three morphometric measurements for (A, B, C) 100 hatchery reared juvenile rainbow trout (Oncorhynchus mykiss) and (D, E, F) 100 inanga (Galaxias maculatus) captured from tributaries of Raglan Harbour, New Zealand, June 2012. Linear regression results are as follows: trout FL (fork length) x D (depth) - R2 = 0.87, F1, 98 = 644.32, P < 0.0001, y = -1.83 + 0.22x; trout FL x W (width) - R2 = 0.71, F1, 98 = 236.52, P < 0.0001, y = -0.18 + 0.11x; trout D X W - R2 = 0.81, F1, 98 = 423.96, P < 0.0001, y = 0.76 + 0.51x; inanga FL x D - R2 = 0.76, F1, 98 = 308.33, P < 0.0001, y = -1.27 + 0.12x; inanga FL x W - R2 = 0.73, F1, 98 = 260.01, P < 0.0001, y = -1.00 + 0.10x; inanga D X W - R2 = 0.89, F1, 98 = 794.02, P < 0.0001, y = 0.15 + 0.74x. Summary statistics of measurements are as follows: trout fork length: 76.36 ± 1.00 mm, min. = 58.00 mm, max. = 109.00 mm; trout depth: 14.73 ± 0.23 mm, min. = 10.84, max = 22.45; trout width: 8.26 ± 0.13 mm, min. = 5.85 mm, max. = 12.22 mm. Inanga fork length: 60.41 ± 1.14 mm, min. = 42.00 mm, max. = 91.00 mm, inanga depth: 6.27 ± 0.16 mm, min. = 3.33 mm, max. = 11.60 mm, inanga width: 4.80 ± 0.13 mm, min. = 2.54 mm, max. = 9.06 mm. The ratio of FL:D:W for juvenile rainbow trout was 1:0.19:0.11 and 1:0.1:0.08 for inanga.

 

Supporting information

Background

To gain an understanding of the more specific needs of migratory fish in successfully overcoming culverts (and ramps), it is important to not only understand swimming capabilities (Tudorache et al. 2008) and fatigue limits (Hammer 1995), but typical morphometric dimensions. While size in general affects the locomotory style of fish (Blake 1983, Mitchell 1989), length alone is not a sufficient predictor of swimming performance when accounting for water conditions such as depth and velocity which impact passage success through culverts and fords (Warren Jr and Pardew 1998). Moreover, fish size is likely highly important for using wetted margins and reduced velocity zones within culverts (Richmond et al. 2007). More specifically, a fish’s ability to propel itself upstream through these structures with shallow, high velocity water is likely to be related to a relationship between water depth within the culvert and the fish’s body dimensions, particularly body depth. For this reason, we measured the fork length (FL), depth (D) and width (W) of inanga (Galaxias maculatus) and juveniles of the introduced salmonid rainbow trout (JRT: Oncorhynchus mykiss). We assessed whether these measurements are consistently linearly related between individuals so that inferences can be made regarding body depth from FL measurements, and for cross-sectional area to understand fishes’ abilities to exploit dead water spaces within remediated culverts. 

Methods

Inanga were collected from several tributaries of the Raglan Harbour, North Island, New Zealand between the 15th and 28th of June, 2012, using both gee-minnow traps (3-mm mesh) and wide-mouth whitebait nets (3-mm mesh, 1060 x 390 mm). Fish were transported to the laboratory in aerated 20-L buckets. One hundred randomly selected fish were chosen for the purpose of this study from a pool of ~1300 collected fish. One thousand JRT were sourced from the Department of Conservation hatchery in Turangi, New Zealand, and 100 were randomly selected. JRT were transported to the laboratory via a specialist fish transfer trailer.

Fish were anaesthetised in an aqueous solution of 2-Phenoxyethanol (200µL/L, Sigma Chemical Co., USA) to assist measurement accuracy. Three measurements (fork length [FL], depth [D] and width [W]) were made on each fish using digital vernier callipers (AIA), accurate to 0.01 mm. D and W were measured at the posterior edge of where the pectoral fin sat at rest.

To predict between body measurements we used linear regression analysis on raw data of all combinations of FL, W and D for each species using R 2.15.1 (R Development Core Team 2011).

Observations

The D x W relationship was the strongest for inanga, suggesting gut fullness and spawning stage had little effect on their morphometry. However, both the regressions involving FL were considerably weaker (R2 < 0.78), with most variation at the smaller size ranges where they transition from migratory juvenile ‘whitebait’ to post-migratory adults. In fact, inanga tend to shrink in length during the transition phase between ‘whitebait’ and adult (McDowall 1990). The source locations of these fish were within or just upstream of the estuarine area of these streams suggesting the presence of both migratory and post-migratory individuals. However, clearly evident unpigmented migratory juveniles were excluded from the original pool of 1000 from which the 100 fish used in this study were randomly selected from.

With the large amount of research assessing culvert remediation (e.g. Macdonald and Davies 2007, David and Hamer 2012), it is important to have an understanding of these morphometrics related to culvert design to maximise the design of remediation tools for specific species. Hence we have provided detailed morphometric information of two common fish species present in New Zealand in the context of fish passage requirements through obstructions such as poorly designed culverts. It is important to bear in mind that these measurements are relevant to culverts where internal hydrodynamics are the barrier and tools such as baffling (Macdonald and Davies 2007) and mussel spat rope (David et al. 2009, Tonkin et al. 2012) are used to break up laminar flows, or where ramps are provided to assist fish past ‘perched’ sections of culverts and into the culvert barrel (Baker and Boubée 2006, Doehring et al. 2011).

These results could potentially be applied to specific culvert remediation where the desired results are to enable passage of natives whilst excluding exotics. For instance, the more tubular form of inanga may enable them to be fully immersed and better negotiate culverts with flow breaking aids such as mussel spat rope at low flows compared to the more ‘wedge-shaped’, deeper bodied JRT. Further, we show that for these two species, strong relationships between the three measurements suggest FL measurements can be used as an overall morphometric measurement of fish size and other dimensions can be accurately predicted. This opens the door for similar work on other species requiring passage assistance to be undertaken so passage assistance tools can be developed accordingly.

Acknowledgements

We would like to thank Mark Hamer, Kris Taipeti and Hayden Hokianga for help collecting fish from the field. The Department of Conservation, Turangi provided the JRT from their hatchery. Fish and Game, Eastern Branch kindly lent the fish transport trailer for transporting the JRT. This research was performed under a Bay of Plenty Polytechnic Animal Ethics Permit.

References

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Author information

Jonathan D. Tonkin

Department of Marine and Environmental Management, Bay of Plenty Polytechnic, Private Bag 12001, Tauranga, New Zealand.

Present address: Department of Environmental Science, Xi'an Jiaotong-Liverpool University, 111 Ren’ai Rd, Dushu Lake Higher Education Town, Suzhou Industrial Park, Suzhou 215123, Jiangsu Province, PR China, E: Jonathan.Tonkin@xjtlu.edu.cn

Bruno O. David

Waikato Regional Council, P.O Box 4010, Hamilton East, New Zealand.

Nathania Brooke

Department of Marine and Environmental Management, Bay of Plenty Polytechnic, Private Bag 12001, Tauranga, New Zealand.