Rattail Fish - Lepidorhynchus denticulatus

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The Story: Rattails or grenadiers, called the latter because many have a protective layer of heavy scales, are a group of deepsea fishes (Figure 1). New Zealand has about 70 different species. Most are small, less than 50 cm total length, but a few grow to over 100 cm. They can be very abundant, e.g., the javelinfish is the second most abundant fish species (after hoki) and the most abundant rattail at bottom depths of 200-800 m on the Campbell Plateau in sub-antarctic New Zealand. Each species prefer to live at particular depths and while a few are found worldwide most are found only in specific areas, e.g., javelinfish prefer depths of 250-600 m and is only found round New Zealand and southern parts of Australia. There are about 10 rattail species found only off New Zealand. Each species of rattail has a preferred diet, some eat crustaceans (prawns, shrimps), including one species that only eats tiny crustaceans called copepods, others prefer polychaetes (marine worms), and some of the larger rattail species eat larger prey including other fishes and squids. They are food for larger fish such as ling and hake and New Zealand Sea Lions.

Some species produce light, using organs in the belly wall containing luminous bacteria. We mostly don't know why they do this but for the javelinfish at least it appears to be able to illuminate its whole underside and reduce its silhouette for a hungry predator looking upwards for food. Males of some species probably produce sound using special muscles on the gas bladder (the buoyancy organ), but again we don't know exactly why they do this.

Useful Links: https://www.niwa.co.nz/fisheries/key-contacts

Classification:Kingdom: Animalia. Phylum: Chordata. Class: Actinopterygii. Order: Gadiformes. Family: Macrouridae. Genus: Lepidorhynchus. Species: denticulatus (Richardson,1846)

The Scientist: Peter McMillan, Fisheries Scientist, NIWA. Peter working on the Tangaroa Research Vessel.

Biological research on Tangaroa trawl surveys aims to estimate fish abundance and collect biological information. For each trawl catch the fish, and all other animals collected, are sorted by species and each species sample is weighed. Subsamples of the most numerous fish are taken and length, weight, and sex are recorded (electronically) for each individual fish in the sample. For some species the otolith is collected and is later (on land) used to estimate age. Peter McMillan has studied the biodiversity i.e., what are the species and how many New Zealand rattails do we have, and along with other workers has described 15 new species.